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Moon and Cassini of Goddard Space Flight Center (GSFC)
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Iapetus Thermal Radiation Im
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| Description |
Iapetus Thermal Radiation Image |
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This image of the infrared heat radiation from Saturn's moon Iapetus was obtained by the Cassini composite infrared spectrometer instrument 16 hours before Cassini's closest approach to this mysterious moon, on December 31, 2004. The thermal radiation is shown as both a grayscale image, equivalent to what we would see if our eyes were sensitive to infrared wavelengths near 15 microns, and as a color-coded temperature map. A previously-released mosaic obtained by Cassini's imaging camera shortly before the composite infrared spectrometer observation, with similar scale and orientation, is also shown for comparison. Temperatures reach nearly 130 Kelvin (-226 Fahrenheit) at noon on the equator on the dark material that covers most of this side of Iapetus, making high noon on Iapetus's dark side probably the warmest places in the Saturn system. This is much warmer than temperatures on another Saturnian moon, Phoebe, measured by composite infrared spectrometer in June 2004. Those Phoebe temperature measurements peaked near 112 Kelvin (-258 Fahrenheit), because though Phoebe is almost as dark as Iapetus's dark material and absorbs nearly as much sunlight, Phoebe rotates much more quickly (once every 9 hours, compared to 79 days for Iapetus). That means the surface has less time to heat up during the day. Temperatures on Iapetus's bright material are much colder, peaking near 100 Kelvin (-280 Fahrenheit), both because the bright material absorbs less sunlight and because it is further from the equator on this side of Iapetus. Temperatures in the large crater near the center of the disc are slightly different from those in surrounding areas, because sloping surfaces within the crater are warmer where they are tilted towards the Sun and cooler when tilted away from the Sun. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission visit, http://saturn.jpl.nasa.gov and the instrument team's home page, http://cirs.gsfc.nasa.gov/. *Credit*: NASA/JPL/GSFC |
| Date |
January 10, 2005 |
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Iapetus Surface Composition
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Iapetus Surface Composition |
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The Cassini visual and infrared mapping spectrometer analyzed the surface composition of Saturn's moon Iapetus as Cassini flew over the polar region on Dec. 31, 2004. The image at left shows the reflectance at 4-microns, which is dominated by the minerals on Iapetus' surface. Two large craters are seen in this image. The polar water ice is relatively dark at this wavelength, so the ice cap is not seen. The next frame shows carbon dioxide on the surface. The carbon dioxide peaks at mid latitudes and shows less strength at the pole and along the equator (the dark band curving near the left edge of the image). The third frame shows the strength of water absorption on Iapetus. The brightest regions are due to water ice near the pole. The grayer areas indicate water bound to minerals on the surface. The color composite shows water as blue, carbon dioxide as green, and non-ice minerals as red. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The visible and infrared mapping spectrometer team is based at the University of Arizona, Tucson. For more information about the Cassini-Huygens mission visit, http://saturn.jpl.nasa.gov. For more information about the visual and infrared mapping spectrometer visit http://wwwvims.lpl.arizona.edu/. *Credit*: NASA/JPL/GSFC |
| Date |
January 10, 2005 |
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Iapetus Temperature Variatio
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Iapetus Temperature Variation Map |
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This plot shows how daytime temperatures at low latitudes on the dark material on Saturn's moon Iapetus vary with time of day, from about 130 Kelvin (-226 Fahrenheit) at noon to about 70 Kelvin (-334 Fahrenheit) at sunset. The observations are compared to a "forecast" model (green line) which predicts temperatures based on an assumed value of a parameter called the "thermal inertia. This measures how well the surface can retain heat as conditions change. Rock or solid ice has a high thermal inertia, roughly 2,000,000 as measured in the obscure units used for thermal inertia, meaning that it is good at storing heat and cools down or heats up relatively slowly. On Iapetus, in contrast, temperatures drop precipitously in the afternoon as the Sun sinks towards the horizon, and a very small value of the thermal inertia (30,000 units) is needed in the model to match the data. This means that Iapetus's surface is extremely bad at storing heat, and is thus extremely fluffy, probably due to the pulverizing effect of billions of years of meteorite impacts, though the mysterious process that has darkened this side of Iapetus may also have played a role. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission visit, http://saturn.jpl.nasa.gov and the instrument team's home page, http://cirs.gsfc.nasa.gov/. *Credit*: NASA/JPL/GSFC |
| Date |
January 10, 2005 |
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Enceladus Keeps the Home Fir
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| Description |
Enceladus Keeps the Home Fires Burning |
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On Nov. 9, 2006, Cassini's composite infrared spectrometer captured its first view of the infrared heat radiation emanating from the "tiger stripe" fractures at the south pole of Saturn's moon Enceladus (right) since the discovery of the hot spot 16 months earlier (left). The original discovery was made just before a close flyby of Enceladus on July 14, 2005, and coincided with the discovery of plumes of water-rich gas and ice particles jetting out of the tiger stripes. However, the spacecraft's orbit did not provide any good views of the south pole for follow-up observations until November 2006. The new observations were made from a range of 110,000 kilometers (68,350 miles), slightly more distant than the 80,000-kilometer range (49,700 miles) of the original observations. Comparison of the two images shows that the south polar region continues to be active, and the distribution of temperatures there has changed little in 16 months. The distribution of heat radiation suggests that most or all of the south polar heat comes from the tiger stripes themselves, though the individual stripes are not resolved at the approximate 30-kilometer (19-mile) spatial resolution of these images. The images show the intensity of heat radiation in the 10- to 16-micron wavelength range, translated into temperature and displayed in false color. Peak south polar temperature on both dates reached about 85 Kelvin (minus 306 degrees Fahrenheit), averaged over the 30-kilometer (19-mile) spatial resolution of the data. However, the variation in brightness with wavelength, which is also measured by the composite infrared spectrometer, reveals that the warm region includes small areas, possibly zones a few 100 meters (320 feet) wide along the length of the tiger stripes, that are at higher temperatures, reaching at least 130 Kelvin (minus 225 degrees Fahrenheit) and perhaps much warmer still. While the south polar tiger stripes are almost certainly heated by energy from the moon's interior, daytime regions at low latitudes are warmed by sunlight to temperatures in the high 70s Kelvin (about minus 320 degrees Fahrenheit). The white numbers on the images show west longitudes on Enceladus, which is 500 kilometers (310 miles) in diameter. The dashed line shows the terminator, the boundary between day and night. The blotchy appearance of the cooler regions away from the south pole, and of the sky beyond the globe of Enceladus, is an artifact resulting from the fact that apart from the polar hot spot, the composite infrared spectrometer can barely detect the very faint heat radiation from this very cold moon. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The, composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov/. The composite infrared spectrometer team homepage is http://cirs.gsfc.nasa.gov/. *Image Credit:* NASA/JPL/GSFC/Southwest Research Institute |
| Date |
December 22, 2006 |
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Warm and Dry on Iapetus
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T |
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The imaging operations center is based at the Space Science Institute in Boulder, Colo. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The composite infrared spectrometer team homepage is http://cirs.gsfc.nasa.gov/. The Cassini imaging team homepage is at http://ciclops.org . Credit: NASA/JPL/GSFC/SwRI/SSI, This image compares midday temperatures on Saturn's moon Iapetus, recorded by the composite infrared spectrometer instrument during Cassini's close Sept. 10, 2007 flyby, with images of the same region recorded during the same flyby by the Cassini imaging science subsystem, shown on the right. See The Other Side of Iapetus for full imaging mosaic. Smallest features visible in the composite infrared spectrometer image (on the left) are about 8 kilometers (5 miles) across. The red rectangle on the visible light (right) image shows the region covered by infrared spectrometer, which extends a distance of 385 kilometers (240 miles) from 36 north, 212 west to 22 south, 220 west. The composite infrared spectrometer determined surface temperatures by measuring the spectrum of infrared radiation emitted by Iapetus in the 9 to 16 micron wavelength range. The dark regions are warmer because they absorb more of the sunlight shining on Iapetus, so dark spots in the visible (right) image show up as warm spots in the infrared image on the left. Temperatures near the equator vary between about 128 Kelvin (minus 229 degrees Fahrenheit) in the darkest regions and about 113 Kelvin (minus 256 degrees Fahrenheit) in the brightest regions. This relatively small temperature difference has a large effect on Iapetus, because at the temperature of the dark regions, a large amount of water ice, which is abundant on most moon surfaces in the Saturn system, can be lost by evaporation over the several-billion year age of Iapetus' surface. Composite infrared spectrometer scientists calculate that when daytime temperatures reach 128 Kelvin (minus 229 degrees Fahrenheit), about 20 meters (65 feet) of ice can be lost per billion years. In the bright regions, with peak temperatures of 113 Kelvin (minus 256 degrees Fahrenheit), only about 10 centimeters, or 2.5 inches, of ice is lost in the same period. It is thus likely that the ice has evaporated completely from the surface of the dark regions of Iapetus, darkening them further, and has collected in the neighboring bright regions, making them brighter, thereby exaggerating initially modest brightness variations. This process is known as thermal segregation. Models by the composite infrared spectrometer team also show that ice evaporated from the warm dark terrain at low latitudes can collect at higher latitudes, and can thus explain the bright polar caps on the dark leading side of Iapetus as well as the relatively dark equatorial regions on the bright trailing side. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. |
| Date |
October 8, 2007 |
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Saturn's Rings, Cold and Col
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Here on the Gallery page you can find the very latest images, videos and products from the Cassini-Huygens mission to Saturn, including the spectacular launch, spacecraft assembly and the exciting trip to Saturn. |
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The varying temperatures of Saturn's rings are depicted here in this false-color image from the Cassini spacecraft. This image represents the most detailed look to date at the temperature of Saturn's rings. The image was made from data taken by Cassini's composite infrared spectrometer instrument. Red represents temperatures of about 110 Kelvin (-261 degrees Fahrenheit), and blue 70 Kelvin (-333 degrees Fahrenheit). Green is equivalent to 90 Kelvin (-298 degrees Fahrenheit). Water freezes at 273 Kelvin (32 degrees Fahrenheit). The spatial resolution of the ring portion of the image is 200 kilometers (124 miles). The data show that the opaque region of the rings, like the outer A ring (on the far right) and the middle B ring, are cooler, while more transparent sections, like the Cassini Division (in red just inside the A ring) or the inner C ring (shown in yellow and red), are relatively warmer. The temperature data were taken on July 1, 2004, of the unlit side of the rings. In order to show the full breadth of the rings, a strip of temperature data was mapped onto a picture of the lit side of the rings taken with the Cassini narrow angle camera on May 11, 2004, a little over a month before Saturn orbit insertion. Cassini is too close to the planet and hence no pictures of the unlit side of the rings are available, so the temperature data were mapped onto a picture of the lit side of rings. Saturn is overexposed and pure white in this picture. Saturn's moon Enceladus is visible below the rings, toward the center. The original picture and caption are available at http://photojournal.jpl.nasa.gov/catalog/PIA05410. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science and Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The Composite Infrared Spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the instrument team's home page, http://cirs.gsfc.nasa.gov . Image Credit: NASA/JPL/GSFC/Ames |
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Saturn's Rings, Cold and Col
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| Description |
Here on the Gallery page you can find the very latest images, videos and products from the Cassini-Huygens mission to Saturn, including the spectacular launch, spacecraft assembly and the exciting trip to Saturn. |
| Full Description |
The varying temperatures of Saturn's rings are depicted here in this false-color image from the Cassini spacecraft. This image represents the most detailed look to date at the temperature of Saturn's rings. The image was made from data taken by Cassini's composite infrared spectrometer instrument. Red represents temperatures of about 110 Kelvin (-261 degrees Fahrenheit), and blue 70 Kelvin (-333 degrees Fahrenheit). Green is equivalent to 90 Kelvin (-298 degrees Fahrenheit). Water freezes at 273 Kelvin (32 degrees Fahrenheit). The spatial resolution of the ring portion of the image is 200 kilometers (124 miles). The data show that the opaque region of the rings, like the outer A ring (on the far right) and the middle B ring, are cooler, while more transparent sections, like the Cassini Division (in red just inside the A ring) or the inner C ring (shown in yellow and red), are relatively warmer. The temperature data were taken on July 1, 2004, of the unlit side of the rings. In order to show the full breadth of the rings, a strip of temperature data was mapped onto a picture of the lit side of the rings taken with the Cassini narrow angle camera on May 11, 2004, a little over a month before Saturn orbit insertion. Cassini is too close to the planet and hence no pictures of the unlit side of the rings are available, so the temperature data were mapped onto a picture of the lit side of rings. Saturn is overexposed and pure white in this picture. Saturn's moon Enceladus is visible below the rings, toward the center. The original picture and caption are available at http://photojournal.jpl.nasa.gov/catalog/PIA05410. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science and Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The Composite Infrared Spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the instrument team's home page, http://cirs.gsfc.nasa.gov . Image Credit: NASA/JPL/GSFC/Ames |
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Warm Fractures on Enceladus
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Warm Fractures on Enceladus |
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This image shows the warmest places in the south polar region of Saturn's moon Enceladus. The unexpected temperatures were discovered by Cassini's composite infrared spectrometer during a close flyby on July 14, 2005. The image shows how these temperatures correspond to the prominent, bluish fractures dubbed "tiger stripes," first imaged by Cassini's imaging science subsystem cameras. Working together the two teams were able to pinpoint the exact location of the warmest regions on Enceladus. The composite infrared spectrometer instrument measured the infrared heat radiation from the surface at wavelengths between 9 and 16.5 microns within each of the 10 squares shown here. Each square is 6 kilometers (4 miles) across. The color of each square, and the number shown above it, describe the composite infrared spectrometer's measurement of the approximate average temperature of the surface within that square. The warmest temperature squares, at 91 and 89 degrees Kelvin (minus 296 and minus 299 degrees Fahrenheit), are located over one of the "tiger stripe" fractures. They contrast sharply with the surrounding temperatures, which are in the range 74 to 81 degrees Kelvin (minus 326 to minus 313 degrees Fahrenheit). The detailed composite infrared spectrometer data suggest that small areas near the fracture are at substantially higher temperatures, well over 100 degrees Kelvin (minus 279 degrees Fahrenheit). Such "warm" temperatures are unlikely to be due to heating of the surface by the feeble sunlight striking Enceladus' south pole. They are a strong indication that internal heat is leaking out of Enceladus and warming the surface along these fractures. Evaporation of this relatively warm ice probably generates the cloud of water vapor detected above Enceladus' south pole by several other Cassini instruments. Scientists are unsure how the internal heat reaches the surface. The process might involve liquid water, slushy brine, or soft but solid ice. The imaging science subsystem image is an enhanced color view with a pixel scale of 122 meters (400 feet) that was acquired at the same time as the composite infrared spectrometer data. It covers a region 125 kilometers (75 miles) across. The spacecraft's distance from Enceladus was 21,000 kilometers (13,000 miles). The broad bluer fractures that can be seen running from the upper left to the lower right of the image are 1 to 2 kilometers (0.6 to 1.2 miles) wide and more than 100 kilometers (60 miles) long. The fractures are thought to be bluer than the surrounding surface because coarser-grained ice (which has a blue color just as thick masses of ice, like glaciers and icebergs, do on Earth) has been exposed in the fractures. The color image was constructed using an ultraviolet filter (centered at 338 nanometers) in the blue channel, a clear filter in the green channel, and an infrared filter (centered at 930 nanometers) in the red channel. The Cassini-Huygens mission is a cooperative project of NASA,, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. The imaging operations center is based at the Space Science Institute in Boulder, Colo. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The composite infrared spectrometer team homepage is http://cirs.gsfc.nasa.gov/ . The imaging team homepage is at http://ciclops.org . Credit: NASA/JPL/GSFC/Space Science Institute |
| Date |
July 29, 2005 |
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Enceladus Temperature Map
| Description |
Enceladus Temperature Map |
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This image shows the surprise that startled Cassini scientists on the composite infrared spectrometer team when they got their first look at the infrared (heat) radiation from the south pole of Saturn's moon Enceladus. There is a dramatic warm spot centered on the pole that is probably a sign of internal heat leaking out of the icy moon. The data were taken during the spacecraft's third flyby of this intriguing moon on July 14, 2005. Based on data from previous flybys, which did not show the south pole well, team members expected that the south pole would be very cold, as shown in the left panel. Enceladus is one of the coldest places in the Saturn system because its extremely bright surface reflects 80 percent of the sunlight that hits it, so only 20 percent is available to heat the surface. As on Earth, the poles should be even colder than the equator because the sun shines at such an oblique angle there. The right hand panel shows a global temperature image made from measurements of Enceladus' heat radiation at wavelengths between 9 and 16.5 microns. Cassini made the observation from a distance of 84,000 kilometers (52,000 miles) on the approach to Enceladus, and the image shows details as small as 25 kilometers (16 miles). Equatorial temperatures are much as expected, topping out at about 80 degrees Kelvin (-315 degrees Fahrenheit), but the south pole is occupied by a well-defined warm region reaching 85 Kelvin (-305 degrees Fahrenheit). That is 15 degrees Kelvin (27 degrees Fahrenheit) warmer than expected. The composite infrared spectrometer data further suggest that small areas of the pole are at even higher temperatures, well over 110 degrees Kelvin (-261 degrees Fahrenheit). Evaporation of this relatively warm ice probably generates the cloud of water vapor detected above Enceladus' south pole by several other Cassini instruments. The south polar temperatures are very difficult to explain if sunlight is the only energy source heating the surface, though exotic sunlight-trapping mechanisms have not yet been completely ruled out. It therefore seems likely that portions of the polar region are warmed by heat escaping from the interior of the moon. This would make Enceladus only the third solid body in the solar system, after Earth and Jupiter's volcanic moon Io, where hot spots powered by internal heat have been detected. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov . The composite infrared spectrometer team homepage is, http://cirs.gsfc.nasa.gov/ . Credit: NASA/JPL/GSFC |
| Date |
July 29, 2005 |
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Phoebe's Radiation
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Phoebe's Radiation |
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This image shows thermal radiation from the day and night sides of Saturn's moon Phoebe, taken by the composite infrared spectrometer onboard Cassini 1.8 hours before the spacecraft's closest approach to Phoebe on June 11, 2004. The left-hand panel displays the image in grayscale format, showing the brightness of Phoebe's radiation in the wavelength range 15-17 microns, which is about 25 times the longest wavelength visible to the naked eye. In the middle panel this brightness is used to estimate the surface temperature distribution across Phoebe. Temperatures are given in degrees Kelvin, and vary from a relatively toasty 107 Kelvin (-267 Fahrenheit), in the late morning near the equator (white, lower right), to less than 75 Kelvin (-324 Fahrenheit) in the northern hemisphere in the pre-dawn hours (dark blue, upper left). The "ragged edge" of Phoebe in this region is an instrumental artifact. Temperatures are affected strongly by topography, as can be seen by comparison with the visible-wavelength image (right). Some of the coldest temperatures are found in the shadowed region inside the large depression in the northern hemisphere (upper right). The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini composite infrared spectrometer home page at http://cirs.gsfc.nasa.gov/ . Image Credit: NASA/JPL/Goddard Space Flight Center |
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Atlas Found!
| Description |
Here on the Gallery page you can find the very latest images, videos and products from the Cassini-Huygens mission to Saturn, including the spectacular launch, spacecraft assembly and the exciting trip to Saturn. |
| Full Description |
The Cassini spacecraft has sighted the tiny moon Atlas, which is seen here for the first time since Voyager 1 flew past Saturn in 1980. Cassini's narrow angle camera captured a sequence of 112 images in visible light, which were used to create a movie of Atlas and other moons racing around the outer edge of Saturn's rings. One of those images is shown here. Over the course of almost five and one-quarter hours, Cassini watched the moons as they circled the planet, snapping 1.2-second exposures about 12 minutes apart. These images were part of a sequence designed specifically to search for small moons near Saturn's F ring. Contrast was enhanced in the images, and the rings themselves were overexposed intentionally, to make these small moons visible. A group of three moons can be seen rounding the right loop of Saturn's rings, followed by a fourth moon. In the first group, the moon exterior to Saturn's thin, knotted F ring is Epimetheus (116 kilometers, 72 miles across), the two moons interior to the F ring are Prometheus (102 kilometers, 63 miles across) and tiny unresolved Atlas (32 kilometers, 20 miles across). The fourth moon seen here, exterior to the F ring and tagging along behind the others, is Pandora (84 kilometers, 52 miles across). At the same time, on the left side, Janus can be seen (181 kilometers, 113 miles across). The view is taken looking upward from Cassini's southern vantage point beneath the ring plane. The moons visible here are orbiting Saturn in a plane that is tilted 67 degrees away from the viewer. These images were taken on May 26 and 27, 2004, from a distance of approximately 19.2 million kilometers (11.9 million miles) from Saturn. The image scale is approximately 114 kilometers (71 miles) per pixel. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo. For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini imaging team home page, http://ciclops.org . Image Credit: NASA/JPL/Goddard Space Flight Center |
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Phoebe Temperature Maps
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Phoebe Temperature Maps |
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A montage of maps of Saturn's moon Phoebe shows surface temperatures at various times of day as determined by the composite infrared spectrometer onboard Cassini during the June 11, 2004, Phoebe flyby. The asterisk on each map shows the location of the subsolar point, where the Sun is directly overhead. This point moves across the surface as Phoebe rotates. It is morning in regions to the left of the subsolar point, and afternoon in regions to the right. Like a newspaper weather map, different colors indicate different temperatures, though Phoebe's temperatures are distinctly cooler than even the coldest January day on Earth. Equatorial temperatures peak in the early afternoon near 112 Kelvin (-257 Fahrenheit), plunging to 78 Kelvin (-319 Fahrenheit) before dawn, and are even colder at higher latitudes. The large day/night temperature contrasts imply that Phoebe's surface is covered in loose dust or ice particles that store little heat and thus cool off rapidly at night. Regions of Phoebe's surface that were not observed are shown in black. Most of the maps show the effect on surface temperatures of the large crater-like depression seen in Cassini's visible-wavelength images of Phoebe, which is located just left of center in these maps. Crater walls that are shadowed and cold in the early morning in the first map are sunlit and warm in the late afternoon in the final map. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Office of Space Science, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the Cassini composite infrared spectrometer home page at http://cirs.gsfc.nasa.gov/ . Image Credit: NASA/JPL/Goddard Space Flight Center |
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Iapetus Temperature Map
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Iapetus Temperature Map |
| Full Description |
This temperature map of Saturn's moon Iapetus is constructed from observations of Iapetus's infrared heat radiation taken with the Cassini composite infrared spectrometer instrument during the Dec. 31, 2004 flyby. The orange asterisk marks the point on Iapetus where the Sun is directly overhead. Temperatures reach nearly 130 Kelvin (-226 Fahrenheit) at noon on the equator on the dark material that covers most of this side of Iapetus, making high noon on Iapetus's dark side probably the warmest places in the Saturn system. This is much warmer than temperatures on the moon Phoebe measured by the composite infrared spectrometer in June 2004, which peaked near 112 Kelvin (-258 Fahrenheit). That's because, although Phoebe is almost as dark as Iapetus's dark material and absorbs nearly as much sunlight, Phoebe rotates much more quickly (once every 9 hours, compared to 79 days for Iapetus). That means the surface has less time to heat up during the day. Temperatures on Iapetus' bright material are much colder, peaking near 100 Kelvin (-280 Fahrenheit), both because the bright material absorbs less sunlight and because it is further from the equator on this side of Iapetus. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. For more information about the Cassini-Huygens mission visit, http://saturn.jpl.nasa.gov and the instrument team's home page, http://cirs.gsfc.nasa.gov/. *Credit*: NASA/JPL/GSFC |
| Date |
January 10, 2005 |
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Searching for Warmth
| Description |
The exciting mystery of an active south polar region on Saturn's icy moon Enceladus continues to unfold as scientists make the correlation between geologically youthful surface fractures and unusually warm temperatures. |
| Full Description |
The exciting mystery of an active south polar region on Saturn's icy moon Enceladus continues to unfold as scientists make the correlation between geologically youthful surface fractures and unusually warm temperatures. This view shows excess heat radiation from cracks near the moon's south pole. These warm fissures are the source of plumes of dust and gas seen by multiple instruments on the Cassini spacecraft during its flyby of Enceladus on July 14, 2005, as described in a series of papers in the March 10, 2006, issue of the journal Science. This image shows two arrays of temperature readings across the surface of Enceladus, as measured by the Cassini composite infrared spectrometer, superimposed on images of the surface taken simultaneously by the imaging science subsystem. Surface temperatures in Kelvin, derived from the intensity of infrared radiation detected by the composite infrared spectrometer, are shown along with their formal uncertainties, although true uncertainties for temperatures below about 75 Kelvin (minus 325 degrees Fahrenheit) are not easily described by a single number. Enhanced thermal emission is seen in the vicinity of the prominent "tiger stripe" fissures discovered by the imaging cameras. In this image, the excess emission is most strongly seen in the left-most composite infrared spectrometer field of view, which includes a fissure near the end of one of the tiger stripes. The peak temperatures, 86 Kelvin and 90 Kelvin (minus 305 and minus 298 degrees Fahrenheit) respectively, are averages over the composite infrared spectrometer field of view, and other composite infrared spectrometer data suggest that much higher temperatures, up to at least 145 Kelvin (minus 199 degrees Fahrenheit), occur in narrow zones a few hundred meters wide along the tiger stripe fissures. See (PIA07794) for a related image. This image is centered near longitude 135 west, latitude 65 south, and each square from the composite infrared spectrometer field of view is 17.5 kilometers (10.9 miles) across. This Cassini narrow-angle camera image has been cropped and resized for presentation. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. The imaging operations center is based at the Space Science Institute in Boulder, Colo. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The composite infrared spectrometer team homepage is http://cirs.gsfc.nasa.gov/. The imaging team homepage is at http://ciclops.org *Credit:* NASA/JPL/GSFC/Space Science Institute |
| Date |
March 9, 2006 |
|
Searching for Warmth
| Description |
The exciting mystery of an active south polar region on Saturn's icy moon Enceladus continues to unfold as scientists make the correlation between geologically youthful surface fractures and unusually warm temperatures. |
| Full Description |
The exciting mystery of an active south polar region on Saturn's icy moon Enceladus continues to unfold as scientists make the correlation between geologically youthful surface fractures and unusually warm temperatures. This view shows excess heat radiation from cracks near the moon's south pole. These warm fissures are the source of plumes of dust and gas seen by multiple instruments on the Cassini spacecraft during its flyby of Enceladus on July 14, 2005, as described in a series of papers in the March 10, 2006, issue of the journal Science. This image shows two arrays of temperature readings across the surface of Enceladus, as measured by the Cassini composite infrared spectrometer, superimposed on images of the surface taken simultaneously by the imaging science subsystem. Surface temperatures in Kelvin, derived from the intensity of infrared radiation detected by composite infrared spectrometer, are shown along with their formal uncertainties, although true uncertainties for temperatures below about 75 Kelvin (minus 325 degrees Fahrenheit) are not easily described by a single number. Enhanced thermal emission is seen in the vicinity of the prominent "tiger stripe" fissures discovered by the imaging cameras. In this image, the excess emission is near the center of the composite infrared spectrometer array, directly over a tiger stripe fissure. The peak temperatures, 86 Kelvin and 90 Kelvin (minus 305 and minus 298 degrees Fahrenheit) respectively, are averages over the composite infrared spectrometer field of view, and other composite and infrared spectrometer data suggest that much higher temperatures, up to at least 145 Kelvin (minus 199 degrees Fahrenheit), occur in narrow zones a few hundred meters wide along the tiger stripe fissures. See (PIA07793) for a related image. This image was taken nearly three times closer to the moon and is centered near longitude 120 west, latitude 82 south, and each composite infrared spectrometer field of view is 6.0 kilometers (3.7 miles) across. This Cassini narrow-angle camera image was cropped and resized for presentation. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The composite infrared spectrometer team is based at NASA's Goddard Space Flight Center, Greenbelt, Md. The imaging operations center is based at the Space Science Institute in Boulder, Colo. For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov. The composite infrared spectrometer team homepage is http://cirs.gsfc.nasa.gov/. The imaging team homepage is at http://ciclops.org *Credit:* NASA/JPL/GSFC/Space Science Institute |
| Date |
March 9, 2006 |
|
Natural Saturn On The Cassin
…
| Title |
Natural Saturn On The Cassini Cruise |
| Explanation |
What could you see approaching Saturn [ http://www.jpl.nasa.gov/cassini/Kids/stories/ ] aboard an interplanetary cruise [ http://www.jpl.nasa.gov:80/cassini/Mission/cruise.html ] ship? Your view would likely resemble this subtly shaded image [ http://oposite.stsci.edu/pubinfo/pr/1998/28/b.html ] of the gorgeous ringed gas giant. Processed by the Hubble Heritage project [ http://heritage.stsci.edu/ ], the picture intentionally avoids overemphasizing color contrasts and presents a natural looking Saturn [ http://heritage.stsci.edu/ public/Oct22/saturn/saturntable.html#caption ] with cloud bands, storms [ http://antwrp.gsfc.nasa.gov/apod/ap951018.html ], nearly edge-on rings [ http://antwrp.gsfc.nasa.gov/apod/ap981018.html ], and the small round shadow of the moon Enceladus near the center of the planet's disk. Of course, seats were not available on the only ship currently enroute [ http://www.jpl.nasa.gov/cassini/ ] - the Cassini spacecraft, launched in 1997 [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] and scheduled to arrive at Saturn [ http://www.jpl.nasa.gov/cassini/today/ ] in the year 2004. After an extended cruise to a world 1,400 million kilometers from the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap960727.html ], Cassini will tour the Saturnian system [ http://www.hawastsoc.org/solar/eng/saturn.htm ], conducting a remote, robotic exploration with software and instruments designed by [ http://www.jpl.nasa.gov/cassini/Partners/ ] denizens of planet Earth. But where is Cassini now [ http://www.jpl.nasa.gov/cassini/today/ ]? Still about 980 million kilometers from Saturn, last Sunday the spacecraft flew by asteroid 2685 Masursky [ http://www.jpl.nasa.gov/cassini/MoreInfo/ sigevents/sigevent000128.html ]. |
|
Sky and Planets
| Title |
Sky and Planets |
| Explanation |
On February 10th, an evocative [ http://www.jps.net/ssumner/ ] evening sky above Rocklin, California, USA inspired astrophotographer Steve Sumner to record this remarkable sight - five planets and the Moon. Near its first quarter phase, the bright Moon [ http://lunar.arc.nasa.gov/ ] was intentionally overexposed but Saturn [ http://www.jpl.nasa.gov/cassini/ ], Jupiter [ http://galileo.jpl.nasa.gov/ ], Mars [ http://mars.jpl.nasa.gov/ ], and Mercury [ http://sd-www.jhuapl.edu/MESSENGER/ ] (and, of course, planet Earth's [ http://www.earth.nasa.gov/ ] horizon) are all clearly visible in the deepening twilight. Notably absent in this grouping of naked-eye planets is Venus [ http://antwrp.gsfc.nasa.gov/apod/ap990903.html ] which is still putting in an early appearance as the morning star [ http://ispec.scibernet.com/station/morn_star.html ]. This month, Mercury has joined Venus in the dawn twilight while Saturn, Jupiter, and Mars still shine brightly in the western sky at nightfall [ http://www.skypub.com/sights/sights.shtml ] making another gorgeous close grouping with the crescent Moon [ http://www.inconstantmoon.com/ ]. |
|
Slightly Beneath Saturn's Ri
…
| Title |
Slightly Beneath Saturn's Ring Plane |
| Explanation |
When orbiting Saturn, be sure to watch for breathtaking superpositions of moon [ http://antwrp.gsfc.nasa.gov/apod/ap051003.html ]s, rings [ http://antwrp.gsfc.nasa.gov/apod/ap040117.html ], and shadow [ http://antwrp.gsfc.nasa.gov/apod/ap040803.html ]s. One such picturesque vista [ http://photojournal.jpl.nasa.gov/catalog/PIA08146 ] was visible recently to the robot Cassini spacecraft [ http://en.wikipedia.org/wiki/Cassini-Huygens ] now orbiting Saturn. In late February, Cassini captured Rhea [ http://en.wikipedia.org/wiki/Rhea_%28moon%29 ], the second largest moon of Saturn, while looking up from slightly beneath Saturn's expansive ring [ http://antwrp.gsfc.nasa.gov/apod/ap051219.html ] plane. Signature dark gaps [ http://www.planetary.org/saturn/rings.html ] are visible in the nearly edge-on rings. A shadow of Saturn's F ring [ http://antwrp.gsfc.nasa.gov/apod/ap041217.html ] cuts across the cratered ice-moon. Cassini is scheduled [ http://saturn.jpl.nasa.gov/operations/saturn-tour.cfm ] to continue sending back images from the orbit of Saturn until at least 2008. |
|
Venus, Moon, and Neighbors
| Title |
Venus, Moon, and Neighbors |
| Explanation |
Rising before the Sun on February 2nd, astrophotographer [ http://pages.prodigy.net/pam.orman/JoeGallery.html ] Joe Orman anticipated [ http://pages.prodigy.net/pam.orman/JoeAlmanac2000.html ] this apparition of the bright morning star [ http://ispec.scibernet.com/station/morn_star.html ] Venus near a lovely crescent Moon above a neighbor's house in suburban Phoenix, Arizona, USA. Fortunately, the alignment of bright planets and the Moon is one of the most inspiring sights in the night sky [ http://www.skypub.com/sights/skyevents/0004skyevents.html ] and one that is often easy to enjoy and share without any special equipment. Take tonight [ http://spacescience.com/headlines/y2000/ast30mar_1m.htm ], for example. Those blessed with clear skies can simply step outside near sunset and view a young crescent Moon very near three bright planets in the west Jupiter [ http://galileo.jpl.nasa.gov/ ], Mars [ http://mars.jpl.nasa.gov/mgs/ ], and Saturn [ http://www.jpl.nasa.gov/cassini/ ]. Jupiter will be the unmistakable brightest star near the Moon with a reddish Mars just to Jupiter's north and pale yellow Saturn directly above. Of course, these sky shows [ http://drumright.ossm.edu/astronomy/conjunctions.html ] create an evocative picture [ http://antwrp.gsfc.nasa.gov/apod/ap000310.html ] but the planets and Moon just appear to be near each other -- they are actually only approximately lined up and lie in widely separated orbits. Unfortunately, next month's highly publicized alignment of planets [ http://www.griffithobs.org/SkyAlignments.html ] on May 5th will be lost from view in the Sun's glare but such planetary alignments [ http://www.skypub.com/news/special/whypanic.html ] occur repeatedly and pose no danger [ http://www.badastronomy.com/bad/misc/planets.html ] to planet Earth. |
|
Saturn in Blue and Gold
| Title |
Saturn in Blue and Gold |
| Explanation |
Why is Saturn partly blue? The above picture [ http://photojournal.jpl.nasa.gov/catalog/PIA08166 ] of Saturn approximates what a human [ http://en.wikipedia.org/wiki/Human ] would see if hovering close to the giant ringed world. The above picture [ http://photojournal.jpl.nasa.gov/catalog/PIA08166 ] was taken in mid-March by the robot Cassini spacecraft [ http://www.esa.int/esaMI/Cassini-Huygens/SEM9D2HHZTD_0.html ] now orbiting Saturn [ http://www.nineplanets.org/saturn.html ]. Here Saturn's majestic rings [ http://en.wikipedia.org/wiki/Saturn%27s_rings ] appear directly only as a thin vertical line. The rings show their complex structure in the dark shadows they create on the image left. Saturn's fountain moon Enceladus [ http://antwrp.gsfc.nasa.gov/apod/ap060310.html ], only about 500 kilometers across, is seen as the bump in the plane of the rings. The northern hemisphere of Saturn can appear partly blue [ http://science.nasa.gov/headlines/y2005/17feb_bluesaturn.htm ] for the same reason that Earth's skies can appear blue [ http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html ] -- molecules in the cloudless portions of both planet's atmospheres are better at scattering blue light than red. When looking deep into Saturn's clouds [ http://antwrp.gsfc.nasa.gov/apod/ap051010.html ], however, the natural gold hue of Saturn's clouds becomes dominant. It is not known why "southern" Saturn does not show the same blue hue -- one hypothesis holds that clouds are higher there. It is also not known [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004cosp.meet..466W ] why Saturn's clouds are colored [ http://antwrp.gsfc.nasa.gov/apod/ap960803.html ] gold. |
|
Planets Above The Clouds
| Title |
Planets Above The Clouds |
| Explanation |
Clouds scatter the faint orange rays of the setting sun [ http://antwrp.gsfc.nasa.gov/apod/ap000115.html ] in the foreground of this breathtaking photograph from the summit [ http://www.ifa.hawaii.edu/mko/mko.html ] of Mauna Kea, Hawaii [ http://antwrp.gsfc.nasa.gov/apod/ap980725.html ]. Taken on April 7th, this skyscape features a dramatic lunar and planetary alignment [ http://antwrp.gsfc.nasa.gov/apod/ap000406.html ]. An overexposed crescent moon [ http://antwrp.gsfc.nasa.gov/apod/ap991108.html ] dominates the celestial scene, but the bright "star" just below and to its right is Saturn [ http://www.jpl.nasa.gov/cassini/Kids/stories/ ] while further below Saturn is a close pairing of brilliant Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap000429.html ] and a fainter, yellowish Mars [ http://marsnt3.jpl.nasa.gov/education/students.html ]. Red giant star Aldebaran [ http://www.bo.astro.it/copernic/alde-eng.html ] is almost directly above the moon near the top of the image and the bright blue stars of the Pleiades cluster [ http://www.aao.gov.au/images.html/captions/uks018.html ] are visible about midway up and to the right of the moon-Aldebaran line. The good news is that planetary alignments [ http://www.skypub.com/news/special/whypanic.html ] like this one do not portend [ http://tech-two.mit.edu/Shakespeare/Tragedy/macbeth/ macbeth.html ] disasters, are relatively common, and can clearly make inspirational viewing for casual stargazers and astronomers alike. The bad [ http://www.badastronomy.com/bad/misc/planets.html ] news is that the world is not going to end because of the highly publicized planetary alignment [ http://www.griffithobs.org/SkyAlignments.html ] occurring tomorrow, May 5th -- so you probably will have to go to work [ http://www.nasa.gov/newsinfo/alignment.html ]! |
|
Ancient Craters on Saturn's
…
| Title |
Ancient Craters on Saturn's Rhea |
| Explanation |
Saturn's ragged moon Rhea has one of the oldest surfaces known. Estimated as changing little in the past billion years, Rhea [ http://en.wikipedia.org/wiki/Rhea_%28moon%29 ] shows craters [ http://en.wikipedia.org/wiki/Impact_crater ] so old they no longer appear round ? their edges have become compromised by more recent cratering. Like Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap051113.html ], Rhea's rotation is locked on Saturn, and the above image [ http://photojournal.jpl.nasa.gov/catalog/PIA08173 ] shows part of Rhea's surface [ http://antwrp.gsfc.nasa.gov/apod/ap051213.html ] that always faces Saturn. Rhea's leading surface is more highly cratered than its trailing surface. Rhea [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search?rhea ] is composed mostly of water-ice but is thought to have a small rocky core. The above image [ http://photojournal.jpl.nasa.gov/catalog/PIA08173 ] was taken by the robot Cassini spacecraft [ http://www.esa.int/esaMI/Cassini-Huygens/SEM9D2HHZTD_0.html ] now orbiting Saturn. Cassini swooped past Rhea two months ago and captured the above image from about 100,000 kilometers away. Rhea [ http://www.nineplanets.org/rhea.html ] spans 1,500 kilometers making it Saturn's second largest moon after Titan [ http://antwrp.gsfc.nasa.gov/apod/ap060215.html ]. Several surface features on Rhea [ http://antwrp.gsfc.nasa.gov/apod/ap050215.html ] remain unexplained including large light patch [ http://antwrp.gsfc.nasa.gov/apod/ap050530.html ]es. |
|
Crescent Rhea Occults Cresce
…
| Title |
Crescent Rhea Occults Crescent Saturn |
| Explanation |
Soft hues, partially lit orbs, a thin trace of the ring, and slight shadows highlight this understated view of the majestic surroundings of the giant planet Saturn. Looking nearly back toward the Sun, the robot Cassini spacecraft [ http://en.wikipedia.org/wiki/Cassini-Huygens ] now orbiting Saturn captured crescent phases [ http://antwrp.gsfc.nasa.gov/apod/ap060618.html ] of Saturn [ http://www.nineplanets.org/saturn.html ] and its moon Rhea [ http://antwrp.gsfc.nasa.gov/apod/ap060530.html ] in color a few months ago. As striking as the above image [ http://photojournal.jpl.nasa.gov/catalog/PIA07806 ] is, it is but a single frame from a recently released 60-frame silent movie where Rhea can be seen gliding in front of its parent world. Since Cassini was nearly in the plane of Saturn's rings [ http://pds-rings.seti.org/saturn/ ], the normally impressive rings are visible here only as a thin line [ http://antwrp.gsfc.nasa.gov/apod/ap051219.html ] across the image center. Cassini has now passed the official half-way mark of its mission around Saturn, but is well situated to complete another two years [ http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=670 ] investigating this complex and surprising system. |
|
Bright Cliffs Across Saturn'
…
| Title |
Bright Cliffs Across Saturn's Moon Dione |
| Explanation |
What causes the bright streaks on Dione? Recent images of this unusual moon by the robot Cassini spacecraft [ http://saturn.jpl.nasa.gov/overview/mission.cfm ] now orbiting Saturn [ http://www.nineplanets.org/saturn.html ] are helping to crack the mystery. Close inspection of Dione's trailing hemisphere, pictured above [ http://photojournal.jpl.nasa.gov/catalog/PIA08256 ], indicates that the white wisps are composed of deep ice cliffs [ http://antwrp.gsfc.nasa.gov/apod/ap051026.html ] dropping hundreds of meters. The cliffs may indicate that Dione has undergone some sort of tectonic surface [ http://www.seismo.unr.edu/ftp/pub/louie/class/100/plate-tectonics.html ] displacements in its past. The bright ice-cliffs run across some of Dione [ http://en.wikipedia.org/wiki/Dione_%28moon%29 ]'s many craters, indicating that the process [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1984Icar...59..205M ] that created them occurred later than the impacts [ http://antwrp.gsfc.nasa.gov/apod/ap010428.html ] that created those craters. Dione [ http://www.nineplanets.org/dione.html ] is made of mostly water ice but its relatively high density indicates that it contains much rock [ http://en.wikipedia.org/wiki/Rock_and_roll ] inside. Giovanni Cassini [ http://www.seds.org/messier/xtra/Bios/cassini.html ] discovered Dione in 1684. The above image [ http://photojournal.jpl.nasa.gov/catalog/PIA08256 ] was taken at the end of July from a distance of about 263,000 kilometers. Other high resolution image [ http://antwrp.gsfc.nasa.gov/apod/ap951009.html ]s of Dione were taken by the passing Voyager spacecraft [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ] in 1980. |
|
Earth from Saturn
| Title |
Earth from Saturn |
| Explanation |
What's that pale blue dot in this image taken from Saturn? Earth [ http://antwrp.gsfc.nasa.gov/apod/ap010204.html ]. The robotic Cassini spacecraft [ http://saturn.jpl.nasa.gov/spacecraft/index.cfm ] looked back toward its old home world earlier this month as it orbited Saturn [ http://en.wikipedia.org/wiki/Saturn_(planet) ]. Using Saturn itself to block the bright Sun [ http://antwrp.gsfc.nasa.gov/apod/ap030530.html ], Cassini imaged a faint dot on the right of the above photograph [ http://photojournal.jpl.nasa.gov/catalog/PIA08324 ]. That dot is expanded on the image inset, where a slight elongation in the direction of Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap030526.html ] is visible [ http://antwrp.gsfc.nasa.gov/apod/ap980904.html ]. Vast water oceans make Earth's reflection of sunlight somewhat blue [ http://www.sciam.com/askexpert_question.cfm?articleID=000CCDD2-DD07-1C71-9EB7809EC588F2D7 ]. Earth is home to over six billion humans [ http://desip.igc.org/populationmaps.html ] and over one octillion [ http://en.wikipedia.org/wiki/Octillion ] Prochlorococcus [ http://sciam.com/article.cfm?chanID=sa022&articleID=0005BE47-0078-1FA8-807883414B7F0000 ]. |
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In the Shadow of Saturn
| Title |
In the Shadow of Saturn |
| Explanation |
In the shadow of Saturn, unexpected wonders appear. The robotic Cassini spacecraft [ http://saturn.jpl.nasa.gov/spacecraft/index.cfm ] now orbiting Saturn [ http://antwrp.gsfc.nasa.gov/apod/saturn.html ] recently drifted in giant planet's shadow [ http://antwrp.gsfc.nasa.gov/apod/ap040926.html ] for about 12 hours and looked back toward the eclipsed Sun [ http://antwrp.gsfc.nasa.gov/apod/ap010408.html ]. Cassini saw a view unlike any other. First, the night side of Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap060912.html ] is seen to be partly lit by light reflected from its own majestic ring system [ http://www.planetary.org/saturn/images_saturn_rings.html ]. Next, the rings themselves appear dark when silhouetted against Saturn, but quite bright when viewed away from Saturn and slightly scattering [ http://www.daviddarling.info/encyclopedia/F/forward_scattering.html ] sunlight, in the above exaggerated color image [ http://photojournal.jpl.nasa.gov/catalog/PIA08329 ]. Saturn's rings light up so much that new rings [ http://photojournal.jpl.nasa.gov/catalog/PIA08322 ] were discovered, although they are hard to see in the above image. Visible in spectacular detail, however, is Saturn's E ring [ http://www.planetary.org/explore/topics/saturn/rings.html ], the ring created by the newly discovered ice-fountains [ http://antwrp.gsfc.nasa.gov/apod/ap051205.html ] of the moon Enceladus [ http://antwrp.gsfc.nasa.gov/apod/ap050906.html ], and the outermost ring visible above. Far in the distance [ http://antwrp.gsfc.nasa.gov/apod/ap060927.html ], visible on the image left just above the bright main rings, is the almost ignorable pale blue dot [ http://en.wikipedia.org/wiki/Pale_Blue_Dot ] of Earth. |
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The Surface of Titan
| Title |
The Surface of Titan |
| Explanation |
If sailing the hydrocarbon [ http://chemscape.santafe.cc.fl.us/chemscape/glossary/hdef.htm#24 ] seas of Titan [ http://antwrp.gsfc.nasa.gov/apod/ap990207.html ], beware of gasoline rain. Such might be a travel advisory [ http://travel.state.gov/travel_warnings.html ] issued one future day for adventurers visiting Titan [ http://antwrp.gsfc.nasa.gov/apod/ap000820.html http://www.seds.org/nineplanets/nineplanets/titan.html ], the largest moon of Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ]. New images of Titan [ http://antwrp.gsfc.nasa.gov/apod/ap951021.html ]'s surface were released [ http://despa.obspm.fr/planeto/titan_pueo.html ] last week from the Canada-France Hawaii Telescope [ http://www.cfht.hawaii.edu/ ] featuring the finest details [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999DPS....31.4103C ] yet resolved. Peering into Titan [ http://ispec.scibernet.com/student-pages/saturn/titan.html ]'s thick smog [ http://www.aqmd.gov/smog/inhealth.html ] atmosphere with infrared [ http://www.us-gemini.noao.edu/public/infrared.html ] light, complex features interpreted as oceans, glaciers [ http://uanews.opi.arizona.edu/cgi-bin/WebObjects/ScienceResearch.woa/wo/XoEuK0m1padNGJ00ob/0.11.0.3?ArticleID=1926 ], and rock became visible. The high-resolution infrared image pictured above [ http://despa.obspm.fr/planeto/titan_pueo.html ] was made possible using an unblurring [ http://antwrp.gsfc.nasa.gov/apod/ap000725.html ] technique called adaptive optics [ http://www.lyot.obspm.fr/adaptive_optics.html ]. The interplanetary probe Cassini [ http://www.jpl.nasa.gov/cassini/ ] will reach Saturn and Titan in 2004 to better explore [ http://antwrp.gsfc.nasa.gov/apod/ap970829.html ] this unusual world. |
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Janus: Potato Shaped Moon of
…
| Title |
Janus: Potato Shaped Moon of Saturn |
| Explanation |
Janus is one of the stranger moons of Saturn. First, Janus [ http://www.planetary.org/explore/topics/saturn/janus.html ] travels in an unusual orbit around Saturn where it periodically trades places with its sister moon Epimetheus [ http://antwrp.gsfc.nasa.gov/apod/ap050429.html ], which typically orbits about 50 kilometers away. Janus [ http://en.wikipedia.org/wiki/Janus_%28moon%29 ], although slightly larger than Epimetheus [ http://antwrp.gsfc.nasa.gov/apod/ap050824.html ], is potato [ http://en.wikipedia.org/wiki/Potato ]-shaped and has a largest diameter of about 190 kilometers. Next, Janus is covered with large craters but strangely appears to lack small craters. One possible reason for this is a fine dust that might cover the small moon, a surface also hypothesized for Pandora [ http://antwrp.gsfc.nasa.gov/apod/ap051123.html ] and Telesto [ http://antwrp.gsfc.nasa.gov/apod/ap060222.html ]. Pictured above [ http://photojournal.jpl.nasa.gov/catalog/PIA08296 ], Janus was captured in front of the cloud tops [ http://antwrp.gsfc.nasa.gov/apod/ap051010.html ] of Saturn [ http://en.wikipedia.org/wiki/Saturn ] in late September. |
|
Mountains of Titan
| Title |
Mountains of Titan |
| Explanation |
Peering through [ http://www.jpl.nasa.gov/news/news.cfm?release=2006-147 ] the thick, hazy atmosphere of Saturn's largest moon, an infrared camera onboard the Cassini [ http://saturn.jpl.nasa.gov/home/index.cfm ] spacecraft recorded this view of the tallest mountains ever seen on Titan [ http://antwrp.gsfc.nasa.gov/apod/ap060508.html ]. Captured during a flyby in late October, the high resolution, false-color mosaic [ http://photojournal.jpl.nasa.gov/catalog/PIA09032 ] shows a mountain range about 150 kilometers long and about 1.5 kilometers high - likened to the Sierra Nevada [ http://en.wikipedia.org/wiki/Sierra_Nevada_(US) ] mountain range of the western United States, planet Earth [ http://earthobservatory.nasa.gov/Newsroom/ NewImages/images.php3?img_id=11270 ]. Along Titan's mountain ridges lie bright deposits, thought to be methane [ http://www.astrobio.net/news/article1886.html ] snow or other organic material. The icy [ http://antwrp.gsfc.nasa.gov/apod/ap050610.html ] mountains of Titan were probably formed like Earth's mid-ocean ridges, from material welling up [ http://www.pbs.org/wgbh/aso/tryit/tectonics/ divergent.html ] to fill gaps created as surface tectonic plates [ http://www.ucmp.berkeley.edu/geology/tectonics.html ] spread apart. |
|
The Ecliptic Plane
| Title |
The Ecliptic Plane |
| Explanation |
The Plane of the Ecliptic is well illustrated in this picture from the 1994 lunar prospecting Clementine spacecraft. Clementine's star tracker camera image reveals (from right to left) the Moon [ http://lunar.arc.nasa.gov/ ] lit by Earthshine, the Sun's corona [ http://antwrp.gsfc.nasa.gov/apod/ap960530.html ] rising over the Moon's dark limb, and the planets Saturn [ http://www.jpl.nasa.gov/cassini/ ], Mars [ http://mars.jpl.nasa.gov/ ], and Mercury [ http://sd-www.jhuapl.edu/MESSENGER/ ]. The ecliptic plane is defined as the imaginary plane containing the Earth's orbit around the Sun. In the course of a year, the Sun's apparent path [ http://www.astro.wisc.edu/~dolan/constellations/extra/Zodiac.html ] through the sky lies in this plane. The Solar System's [ http://space.jpl.nasa.gov/ ] planetary bodies all tend to lie near this plane, since they were formed from the Sun's spinning, flattened, proto-planetary disk [ http://antwrp.gsfc.nasa.gov/apod/ap990611.html ]. The snapshot above nicely captures a momentary line-up looking out along this fundamental plane of our Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap990505.html ]. |
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Cassini Spacecraft Approache
…
| Title |
Cassini Spacecraft Approaches Jupiter |
| Explanation |
A new spacecraft has entered the outer Solar System: Cassini [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ]. Launched in 1997 [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] and bound for Saturn in 2004, Cassini sent back the above image [ http://ciclops.lpl.arizona.edu/ciclops/Images_jupiter.html ] last week while approaching the giant planet Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ]. Cassini [ http://quest.arc.nasa.gov/saturn/qa/cassini/ ] joins the Galileo spacecraft [ http://www.jpl.nasa.gov/galileo/mission.html] currently in orbit around Jupiter in studying the gas giant and its moons. In fact, observations [ http://www.jpl.nasa.gov/releases/2000/glextended.html ] involving both spacecraft [ http://www.jpl.nasa.gov/jupiterflyby/ ] simultaneously are planned in the coming months. This color picture [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA02972 ] was taken when Cassini was 81.3 million kilometers from Jupiter. The alternating dark and bright bands characteristic of Jupiter's cloud tops [ http://antwrp.gsfc.nasa.gov/apod/ap000429.html ] can be easily seen. Jupiter's moon Europa [ http://antwrp.gsfc.nasa.gov/apod/ap000825.html ] is also seen at the far right of the image casting a round shadow on the planet. |
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New Moons For Saturn
| Title |
New Moons For Saturn |
| Explanation |
Which planet has the most moons? For now, it's Saturn. Four newly discovered [ http://www.eso.org/outreach/press-rel/pr-2000/ phot-29-00.html ] satellites bring the ringed planet's total to twenty-two, just edging out Uranus' [ http://antwrp.gsfc.nasa.gov/apod/ap971103.html ] twenty-one for the most known [ http://www.eso.org/outreach/press-rel/pr-2000/ phot-19-00.html ] moons in the solar system. Of course, the newfound Saturnian satellites [ http://www.nasm.edu/ceps/etp/saturn/satmoons.html ] are not large [ http://antwrp.gsfc.nasa.gov/apod/ap000820.html ] and photogenic [ http://antwrp.gsfc.nasa.gov/apod/ap000129.html ]. The faint S/2000 S 1, the first discovered in the year 2000, is the tiny dot indicated at the lower right of this August 7th image made with the ESO 2.2 meter telescope at La Silla, Chile [ http://www.ls.eso.org/index.html ]. (An eye-catching spiral galaxy at the upper left is in the very distant background!) Unlike Saturn's larger moons whose almost circular orbits lie near the planet's equatorial plane, all four newly discovered moons have irregular [ http://www.obs-nice.fr/gladman/urhome.html ], skewed orbits drifting far from the planet. With sizes in the 10 to 50 kilometer range, they are are likely captured asteroids. The international team of astronomers involved in the discoveries hopes to get many observations of the tiny satellites [ http://www.obs-nice.fr/saturn/ ] allowing accurate orbital computations before Saturn is [ http://www.jpl.nasa.gov/cassini/ ] lost in the solar glare around March 2001. The team has also found several other irregular satellite candidates which are now being followed. Saturn's only previously known irregular satellite is Phoebe [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ phoebe.html ], discovered over 100 years ago by W. H. Pickering, |
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Liquid Lakes on Saturn's Tit
…
| Title |
Liquid Lakes on Saturn's Titan |
| Explanation |
Why would some regions on Titan reflect very little radar? The leading explanation is that these regions are lakes, possibly composed of liquid methane. The above image [ http://photojournal.jpl.nasa.gov/catalog/PIA09102 ] is a false-color synthetic radar map of a northern region of Titan [ http://saturn.astrobio.net/news/article50.html ] taken during a flyby of the cloudy moon [ http://antwrp.gsfc.nasa.gov/apod/ap040810.html ] by the robotic Cassini spacecraft [ http://en.wikipedia.org/wiki/Cassini-Huygens ] last July. On this map, which spans about 150 kilometers across, dark regions reflect relatively little of the broadcast radar [ http://earth.rice.edu/mtpe/geo/geosphere/topics/remotesensing/25_radar.html ] signal. Images like this show Titan [ http://antwrp.gsfc.nasa.gov/apod/ap050117.html ] to be only the second body in the Solar System [ http://space.jpl.nasa.gov/ ] to possess liquids on the surface. Future observations from Cassini during Titan flybys [ http://saturn.jpl.nasa.gov/operations/saturn-tour.cfm ] will further test the methane [ http://en.wikipedia.org/wiki/Methane ] lake hypothesis, as comparative wind effects on the regions are studied. |
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Jupiter Eyes Ganymede
| Title |
Jupiter Eyes Ganymede |
| Explanation |
Who keeps an eye [ http://ciclops.lpl.arizona.edu/ciclops/ images_jupiter.html ] on the largest moon in the Solar System [ http://www.seds.org/nineplanets/nineplanets/overview.html ]? This moon, visible on the lower right, is Ganymede [ http://www.seds.org/nineplanets/nineplanets/ganymede.html ], and the planet it orbits, Jupiter [ http://antwrp.gsfc.nasa.gov/apod/jupiter.html ], seems to be keeping a watchful eye, as its Great Red Spot [ http://antwrp.gsfc.nasa.gov/apod/ap960802.html ] appears serendipitously nearby. This recently released [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02837 ] enhanced-contrast image from the robot spacecraft Cassini [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ] captures new details of the incredible intricacies of Jupiter's complex cloud [ http://antwrp.gsfc.nasa.gov/apod/ap000429.html ] patterns. Features as small as 250 kilometers can be seen. Counter-clockwise rotating high-pressure white ovals [ http://antwrp.gsfc.nasa.gov/apod/ap990105.html ] that are similar to the Great Red Spot [ http://antwrp.gsfc.nasa.gov/apod/ap001123.html ] appear in the red band below the spot. Between these spots are darker low-pressure systems [ http://www.usatoday.com/weather/wlowpres.htm ] that rotate clockwise. The hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ] and helium [ http://pearl1.lanl.gov/periodic/elements/2.html ] that compose most of Jupiter's clouds is nearly invisible - the trace chemicals that give Jupiter these colors remain unknown [ http://antwrp.gsfc.nasa.gov/apod/ap960803.html ]. The Cassini spacecraft [ http://quest.arc.nasa.gov/saturn/qa/cassini/ ] is using Jupiter [ http://www.hawastsoc.org/solar/eng/jupiter.htm ] to pull it [ http://www.science.nasa.gov/newhome/headlines/ast24jun99_1.htm#gravityassist ] toward Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ], where it is scheduled [ http://www.jpl.nasa.gov/cassini/Mission/cruise.html ] to arrive in 2004. |
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Jupiter, Europa, and Callist
…
| Title |
Jupiter, Europa, and Callisto |
| Explanation |
As the robot Cassini spacecraft [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ] rounds Jupiter [ http://www.jpl.nasa.gov/galileo/jupiter/jupiter.html ] on its way toward Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ], it has taken a sequence of images [ http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html ] of the gas giant with its four largest moons [ http://antwrp.gsfc.nasa.gov/apod/ap001118.html ]. Previously released images have highlighted Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap001212.html ] and Io [ http://antwrp.gsfc.nasa.gov/apod/ap001226.html ]. Pictured above [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02861 ] are the two remaining Galilean satellites [ http://www.jpl.nasa.gov/galileo/ganymede/discovery.html ]: Europa [ http://www.hawastsoc.org/solar/eng/europa.htm ] and Callisto [ http://cass.jsc.nasa.gov/pub/research/outerp/call.html ]. Europa [ http://www.jpl.nasa.gov/galileo/moons/europa.html ] is the bright moon superposed near Jupiter's Great Red Spot [ http://antwrp.gsfc.nasa.gov/apod/ap001123.html ], while Callisto is the dark moon near the frame edge. Callisto [ http://www.jpl.nasa.gov/galileo/moons/callisto.html ] is so dark that it would be hard to see here if its brightness was not digitally enhanced. Recent evidence indicates [ http://www.jpl.nasa.gov/galileo/news/release/press001216.html ] that both moons hold salt-water seas under surface ice that might be home to extra-terrestrial life. By noting the times that moons disappeared and reappeared behind Jupiter in 1676, Ole Roemer [ http://es.rice.edu/ES/humsoc/Galileo/Catalog/Files/roemer.html ] was able to make the first accurate estimation of the speed of light [ http://www.stats.uwaterloo.ca/~rwoldfor/papers/sci-method/paperrev/node4.html ]. |
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Enceladus Creates Saturn's E
…
| Title |
Enceladus Creates Saturn's E Ring |
| Explanation |
The active moon Enceladus appears to be making Saturn's E ring. An amazing picture [ http://ciclops.org/view.php?id=2231 ] showing the moon at work was taken late last year by the Saturn-orbiting Cassini spacecraft [ http://saturn.jpl.nasa.gov/spacecraft/ ] and is shown above [ http://photojournal.jpl.nasa.gov/catalog/PIA08321 ]. Enceladus [ http://en.wikipedia.org/wiki/Enceladus_%28moon%29 ] is the dark spot inside the bright flare, right near the center of Saturn's E ring [ http://en.wikipedia.org/wiki/Rings_of_Saturn#E_Ring ]. Streams of ice and water vapor can be seen pouring off Enceladus [ http://antwrp.gsfc.nasa.gov/apod/ap051205.html ] into the E ring. The above bright image of the normally faint E-ring [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2006Sci...311.1416S ] was made possible by aligning Cassini so that Saturn blocked [ http://antwrp.gsfc.nasa.gov/apod/ap061016.html ] the Sun. From that perspective, small ring particles reflect incoming sunlight [ http://antwrp.gsfc.nasa.gov/apod/ap011030.html ] more efficiently. Cassini has now been orbiting Saturn for almost three years, and is scheduled to swoop [ http://planetary.org/explore/topics/cassini_huygens/tour.html ] by the unexpectedly cryovolcanic [ http://en.wikipedia.org/wiki/Cryovolcano ] Enceladus at least several more times. |
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Nashville Four Planet Skylin
…
| Title |
Nashville Four Planet Skyline |
| Explanation |
So far this February, evening skies [ http://antwrp.gsfc.nasa.gov/apod/ap000504.html ] have been blessed with a glorious Moon and three bright planets, Venus [ http://www.library.utoronto.ca/utel/rp/poems/ longfe10.html ], Jupiter, and Saturn. But just last week, on January 30th, an extreme wide-angle lens allowed astrophotographer Larry Koehn to capture this twilight view of Moon and four planets above [ http://www.seds.org/nineplanets/nineplanets/ see.html ] Nashville, Tennessee, USA. These major solar system [ http://space.jpl.nasa.gov/ ] bodies lie along the ecliptic plane [ http://antwrp.gsfc.nasa.gov/apod/ap001014.html ] and so follow a diagonal line through the picture. Starting near the upper left corner is bright Jupiter [ http://starchild.gsfc.nasa.gov/docs/StarChild/ solar_system_level2/jupiter.html ], which takes on a slightly triangular shape due to the lens distortion. Just below and right of Jupiter is Saturn [ http://www.jpl.nasa.gov/cassini/english/kids/ saturn_in_sky.html ]. Continuing along the diagonal toward the lower right is an overexposed, six day old Moon [ http://www.inconstantmoon.com/ ] and brilliant Venus seemingly embedded in clouds. The fourth planet pictured is Mercury. Notoriously hard to see from planet Earth because it never wanders far from the Sun, Mercury is [ http://antwrp.gsfc.nasa.gov/apod/ap991111.html ] visible just above the lower right corner. The line from Jupiter to Mercury spans about 92 degrees across the Nashville sky. |
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Liquid Sea on Saturn's Titan
| Title |
Liquid Sea on Saturn's Titan |
| Explanation |
What is this vast dark region on Titan? Quite possible a sea of liquid hydrocarbons [ http://en.wikipedia.org/wiki/Hydrocarbon ]. The region was imaged earlier this month when the robotic Cassini spacecraft [ http://en.wikipedia.org/wiki/Cassini_spacecraft ] swooped past Saturn's cloudy moon and illuminated part of it with radar. The dark region in the above image [ http://photojournal.jpl.nasa.gov/catalog/PIA09211 ] reflected little radar, an effect expected were the dark surface [ http://antwrp.gsfc.nasa.gov/apod/ap070207.html ] relatively flat, as expected for a liquid. Other indications that the vast dark area is liquid include the coastline-like topology [ http://antwrp.gsfc.nasa.gov/apod/ap050124.html ] of the brighter regions, which appear to include islands, inlets [ http://antwrp.gsfc.nasa.gov/apod/ap971108.html ], and tributary channels. The uninterrupted smoothness of much of the dark sea may indicate that the sea runs deep, with speculation [ http://photojournal.jpl.nasa.gov/catalog/PIA09211 ] holding a depth estimate of tens of meters. A hydrocarbon sea [ http://photojournal.jpl.nasa.gov/catalog/PIA08930 ] on Titan [ http://en.wikipedia.org/wiki/Titan_%28moon%29 ] holds particular interest for exobiologists [ http://exobiology.nasa.gov/ssx/exobiology.html ] as it might be a place where life could develop. In 2005 the Huygens probe landed on Titan and returned the first surface image [ http://antwrp.gsfc.nasa.gov/apod/ap050117.html ]s. Cassini will continue to explore Titan, as 13 more flybys [ http://saturn.jpl.nasa.gov/operations/saturn-tour.cfm ] are planned. |
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Io: Moon Over Jupiter
| Title |
Io: Moon Over Jupiter |
| Explanation |
How big is the Jovian moon Io [ http://www.seds.org/nineplanets/ nineplanets/io.html ]? The most volcanic body [ http://volcano.und.nodak.edu/vwdocs/planet_volcano/ other_worlds.html ] in the Solar System, Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the size of planet Earth's single large natural satellite [ http://antwrp.gsfc.nasa.gov/apod/ap010127.html ]. Gliding past Jupiter [ http://www.jpl.nasa.gov/jupiterflyby/ ] at the turn of the millennium, the Cassini spacecraft captured this awe inspiring view [ http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html ] of active Io [ http://www.jpl.nasa.gov/galileo/moons/io.html ] with the largest [ http://www.seds.org/nineplanets/nineplanets/ datamax.html ] gas giant as a backdrop, offering a stunning demonstration of the ruling planet's relative size [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/ jupiterfact.html ]. Although in the picture Io [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA02879 ] appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/ joviansatfact.html ]. That puts it nearly 350,000 kilometers above Jupiter's cloud tops [ http://antwrp.gsfc.nasa.gov/apod/ap010215.html ], roughly equivalent to the distance between Earth and Moon [ http://antwrp.gsfc.nasa.gov/apod/ap980904.html ]. The Cassini spacecraft [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ] itself was about 10 million kilometers from Jupiter when recording the image data. |
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Unusual Cratering on Saturn'
…
| Title |
Unusual Cratering on Saturn's Dione |
| Explanation |
Why does one half of Dione have more craters than the other? Start with the fact that Saturn [ http://en.wikipedia.org/wiki/Saturn ]'s moon Dione always has one side that faces Saturn, and always has one side that faces away. This is similar to Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap051113.html ]. This tidal locking [ http://en.wikipedia.org/wiki/Tidal_locking ] means that one side of Dione [ http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sat_Dione ] always leads as the moon progresses in its orbit, while the other side always trails. Dione [ http://en.wikipedia.org/wiki/Dione_%28moon%29 ] should therefore have undergone a significant amount of impacts on its leading half. But the current leading half of Dione [ http://antwrp.gsfc.nasa.gov/apod/ap060905.html ] is less cratered than the trailing half! A possible explanation is that some impacts were so large they spun Dione [ http://www.lpi.usra.edu/meetings/lpsc2005/pdf/2034.pdf ], sometimes changing the part that suffered the highest impact rate before the moon's spin again became locked. Pictured above [ http://photojournal.jpl.nasa.gov/catalog/PIA08956 ], it is the top part of Dione that appears significantly more cratered than the bottom half. |
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Iapetus: 3D Equatorial Ridge
| Title |
Iapetus: 3D Equatorial Ridge |
| Explanation |
This bizarre, equatorial ridge extending across and beyond the dark, leading hemisphere of Iapetus [ http://www.nineplanets.org/iapetus.html ] gives the two-toned [ http://antwrp.gsfc.nasa.gov/apod/ap070914.html ] Saturnian [ http://en.wikipedia.org/wiki/ Saturn%27s_moons_in_fiction#Iapetus ] moon a distinct walnut shape. With red/blue [ http://photojournal.jpl.nasa.gov/Help/ VendorList.html#Glasses ] glasses you can check out a remarkable stereo composition of this extraordinary feature -- based on close-up images from this week's Cassini spacecraft flyby [ http://hownow.brownpau.com/archives/2007/09/ iapetus_flyover_gif/ ]. In fact, the ridge's combination of equatorial symmetry and scale, about 20 kilometers wide and reaching up to 20 kilometers above the surface, is not known to be duplicated anywhere else in our solar system. The unique feature was discovered in [ http://saturn.jpl.nasa.gov/multimedia/images/ image-details.cfm?imageID=1270 ] Cassini images from 2004. It appears to be heavily cratered and therefore ancient, but the origin of the equatorial ridge [ http://en.wikipedia.org/wiki/ Iapetus_%28moon%29#The_equatorial_ridge ] on Iapetus [ http://en.wikipedia.org/wiki/ 2001:_A_Space_Odyssey_(novel)#Differences_with_the_film ] remains a mystery. |
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4,000 Kilometers Above Satur
…
| Title |
4,000 Kilometers Above Saturn's Iapetus |
| Explanation |
What does the surface of Saturn's mysterious moon Iapetus look like? To help find out, the robotic Cassini spacecraft [ http://en.wikipedia.org/wiki/Cassini_spacecraft ] now orbiting Saturn [ http://www.nineplanets.org/saturn.html ] was sent soaring last week just 2,000 kilometers from the unique equatorial ridge of the unusual walnut-shaped [ http://antwrp.gsfc.nasa.gov/apod/ap050201.html ] two-toned moon [ http://antwrp.gsfc.nasa.gov/apod/ap060103.html ]. The above image [ http://antwrp.gsfc.nasa.gov/apod/ap070919.html http://photojournal.jpl.nasa.gov/catalog/PIA08372 ] from Cassini is from about 4,000 kilometers out and allows objects under 100-meters across to be resolved. Cassini found an ancient and battered landscape [ http://antwrp.gsfc.nasa.gov/apod/ap051213.html ] of craters, sloping hills, and mountains as high as 10 kilometers and so rival [ http://en.wikipedia.org/wiki/Everest ] the 8.8-kilometer height of Mt. Everest [ http://antwrp.gsfc.nasa.gov/apod/ap070408.html ] on Earth. Just above the center of this image [ http://photojournal.jpl.nasa.gov/catalog/PIA08372 ] is a small bright patch where an impacting rock might have uncovered deep clean water ice. Space scientists [ http://www.aas.org/dps/ ] will be studying flyby images like this for clues to the origin of Iapetus' unusual shape [ http://antwrp.gsfc.nasa.gov/apod/ap070915.html ] and coloring [ http://antwrp.gsfc.nasa.gov/apod/ap070914.html ] with particular emphasis because no more close flybys [ http://saturn.jpl.nasa.gov/news/events/iapetus/index.cfm ] of the enigmatic world are planned. APOD editor to review best space pictures in Philadelphia next Wednesday [ http://www.rittenhouseastronomicalsociety.org/ ] |
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Iapetus in Black and White
| Title |
Iapetus in Black and White |
| Explanation |
Iapetus, Saturn's [ http://saturn.jpl.nasa.gov/science/moons/ moonDetails.cfm?pageID=7 ] third largest moon, is a candidate for the strangest moon of Saturn. Tidally locked [ http://en.wikipedia.org/wiki/Tidal_locking ] in its orbit around the ringed gas giant, Iapetus is sometimes called the yin-yang moon [ http://www.planetary.org/news/2007/ 0906_Cassini_Zeroes_in_on_Saturns_YinYang.html ] because [ http://en.wikipedia.org/wiki/Image:Yin_yang.svg ] its leading hemisphere is very dark, reflecting about 5 percent of the Sun's light, while its trailing hemisphere is almost as bright as snow. This recent Cassini [ http://www.nasa.gov/mission_pages/cassini/media/ cassini20070912.html ] spacecraft flyby image [ http://photojournal.jpl.nasa.gov/catalog/PIA08374 ] is one of the closest views ever. It spans about 35 kilometers across a cratered transition [ http://www.planetary.org/blog/article/00001130/ ] zone between bright and dark terrain. Iapetus itself has a density close to that of water ice, but the detailed reflective properties of the dark material suggest an organic composition. Honoring the moon's discoverer, the dark terrain is called Cassini [ http://messier.obspm.fr/xtra/Bios/cassini.html ] Regio. |
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The Great Basin on Saturn's
…
| Title |
The Great Basin on Saturn's Tethys |
| Explanation |
Some moons wouldn't survive the collision. Tethys [ http://en.wikipedia.org/wiki/Tethys_%28moon%29 ], one of Saturn's larger moons [ http://www.nineplanets.org/saturn.html ] at about 1000 kilometers in diameter, survived the collision, but sports today the expansive impact crater [ http://antwrp.gsfc.nasa.gov/apod/ap010428.html ] Odysseus. Sometimes called the Great Basin [ http://antwrp.gsfc.nasa.gov/apod/ap060208.html ], Odysseus [ http://en.wikipedia.org/wiki/Odysseus_%28crater%29 ] occurs on the leading hemisphere of Tethys [ http://en.wikipedia.org/wiki/Tethys_%28mythology%29 ] and shows its great age by the relative amount of smaller craters that occur inside its towering walls [ http://antwrp.gsfc.nasa.gov/apod/ap050315.html ]. Another large crater, Melanthius [ http://en.wikipedia.org/wiki/Melanthius ], is visible near the moon's terminator [ http://antwrp.gsfc.nasa.gov/apod/ap050611.html ]. The density of Tethys is similar to water-ice [ http://www.lsbu.ac.uk/water/phase.html ]. The above digitally enhanced image [ http://photojournal.jpl.nasa.gov/catalog/PIA09017 ] was captured in July by the robot Cassini spacecraft [ http://saturn.jpl.nasa.gov/operations/index.cfm ] in orbit around Saturn as it swooped past the giant ice ball [ http://www.chemistry.org/portal/a/c/s/1/feature_tea.html?DOC=teachers%5Ctea_megacryometeors.html ]. |
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Enceladus Ice Geysers
| Title |
Enceladus Ice Geysers |
| Explanation |
Ice geysers erupt on Enceladus [ http://en.wikipedia.org/wiki/Enceladus_%28moon%29 ], bright and shiny inner moon of Saturn. Shown in this false-color image [ http://photojournal.jpl.nasa.gov/catalog/PIA08386 ], a backlit view of the moon's southern limb, the majestic, icy plumes were discovered by [ http://antwrp.gsfc.nasa.gov/apod/ap051205.html ] instruments on the Cassini Spacecraft during close encounters with Enceladus in November of 2005. Eight source locations [ http://saturn.jpl.nasa.gov/news/ press-release-details.cfm?newsID=780 ] for these geysers have now been identified along substantial surface fractures [ http://antwrp.gsfc.nasa.gov/apod/ap060310.html ] in the moon's south polar region. Researchers suspect the geysers arise [ http://photojournal.jpl.nasa.gov/catalog/PIA07799 ] from near-surface pockets of liquid water with temperatures [ http://lamar.colostate.edu/~hillger/temps.htm ] near 273 kelvins (0 degrees C). That's hot when compared to the distant moon's surface temperature of 73 kelvins (-200 degrees C). The cryovolcanism [ http://en.wikipedia.org/wiki/Cryovolcanism ] is a dramatic sign that tiny, 500km-diameter Enceladus is surprisingly [ http://saturn.jpl.nasa.gov/news/ press-release-details.cfm?newsID=662 ] active. Enceladus ice geysers also likely produce Saturn's faint but extended E ring [ http://www.planetary.org/saturn/rings.html ]. |
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The Strange Trailing Side of
…
| Title |
The Strange Trailing Side of Saturn's Iapetus |
| Explanation |
What has happened to Saturn's moon Iapetus? Vast sections of this strange world [ http://en.wikipedia.org/wiki/Iapetus_%28moon%29 ] are dark as coal [ http://en.wikipedia.org/wiki/Coal ], while others are as bright as ice. The composition of the dark material is unknown, but infrared [ http://science.hq.nasa.gov/kids/imagers/ems/infrared.html ] spectra [ http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html ] indicate that it possibly contains some dark form of carbon [ http://periodic.lanl.gov/elements/6.html ]. Iapetus also has an unusual equatorial ridge [ http://antwrp.gsfc.nasa.gov/apod/ap050201.html ] that makes it appear like a walnut [ http://www.whfoods.com/genpage.php?tname=foodspice&dbid=99 ]. To help better understand this mysterious moon, NASA [ http://www.nasa.gov/about/highlights/index.html ] directed the robotic Cassini spacecraft [ http://en.wikipedia.org/wiki/Cassini_spacecraft ] orbiting Saturn to swoop within 2,000 kilometers [ http://antwrp.gsfc.nasa.gov/apod/ap070919.html ] just last month. Pictured above [ http://photojournal.jpl.nasa.gov/catalog/PIA08384 ], from about 75,000 kilometers out, Cassini's trajectory allowed unprecedented imaging of the hemisphere of Iapetus that is always trailing [ http://en.wikipedia.org/wiki/Tidal_locking ]. A huge impact crater seen in the south spans a tremendous 450 kilometers and appears superposed on an older crater [ http://antwrp.gsfc.nasa.gov/apod/ap060530.html ] of similar size. The dark material [ http://antwrp.gsfc.nasa.gov/apod/ap070914.html ] is seen increasingly coating the easternmost part of Iapetus [ http://antwrp.gsfc.nasa.gov/apod/ap060103.html ], darkening craters and highlands alike. Close inspection [ http://micro.magnet.fsu.edu/primer/java/scienceopticsu/powersof10/ ] indicates that the dark coating typically faces the moon's equator. Whether Iapetus' colors are the result of unusual [ http://antwrp.gsfc.nasa.gov/apod/ap061114.html ] episodes of internal volcanism [ http://antwrp.gsfc.nasa.gov/apod/ap051002.html ] or external splattering [ http://antwrp.gsfc.nasa.gov/apod/ap051205.html ] remains unknown. This and other images from Cassini's Iapetus flyby [ http://saturn.jpl.nasa.gov/multimedia/images/image-details.cfm?imageID=1270 ] are being studied for even greater clues. |
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Saturn's Ancient Rings
| Title |
Saturn's Ancient Rings |
| Explanation |
How old are Saturn's rings? No one is quite sure. One possibility is that the rings formed relatively recently in our Solar System's history, perhaps only about 100 million years ago when a moon-sized object broke up [ http://en.wikipedia.org/wiki/Roche_limit ] near Saturn. Evidence for a young ring age includes a basic stability analysis for rings [ http://adsabs.harvard.edu/abs/2007AJ....133..656V ], and the fact that the rings are so bright and relatively unaffected by numerous small dark meteor [ http://antwrp.gsfc.nasa.gov/apod/ap011118.html ] impacts. New evidence [ http://www.jpl.nasa.gov/news/news.cfm?release=2007-149 ], however, raises the possibility that some of Saturn's rings [ http://en.wikipedia.org/wiki/Saturn%27s_rings ] may be billions of years old and so almost as old [ http://en.wikipedia.org/wiki/Edna_Parker ] as Saturn itself. Inspection of images by the Saturn-orbiting Cassini spacecraft indicates that some of Saturn's ring [ http://antwrp.gsfc.nasa.gov/apod/ap040723.html ] particles temporarily bunch and collide, effectively recycling ring [ http://antwrp.gsfc.nasa.gov/apod/ap071024.html ] particles by bringing fresh bright ices to the surface. Seen here [ http://photojournal.jpl.nasa.gov/catalog/PIA09788 ], Saturn's rings were imaged in their true colors by the robotic Cassini [ http://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens ] in late October. Icy bright Tethys [ http://antwrp.gsfc.nasa.gov/apod/ap070909.html ], a moon of Saturn likely brightened by a sandblasting rain of ice [ http://antwrp.gsfc.nasa.gov/apod/ap071013.html ] from sister moon Enceladus [ http://antwrp.gsfc.nasa.gov/apod/ap060310.html ], is visible in front of the darker rings. |
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A Portrait of Saturn from Ti
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| Title |
A Portrait of Saturn from Titan |
| Explanation |
This artistic portrait [ http://sci.esa.int/content/searchimage/ searchresult.cfm?aid=12&cid=387&ooid=18425 ] of Saturn [ http://www.otenet.gr/everyday/ saturday.html ] depicts how it might look from Titan [ http://www.seds.org/nineplanets/nineplanets/ titan.html ], Saturn's largest moon. In the foreground sits ESA's Huygens probe [ http://sci.esa.int/home/huygens/index.cfm ], which will be released by NASA's Cassini spacecraft [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ] and parachute to Titan's surface. Cassini will [ http://www.jpl.nasa.gov/cassini/english/ ] reach Saturn in 2004 and release the Huygens probe [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ probe.html ] later that year. Titan [ http://antwrp.gsfc.nasa.gov/apod/ap000820.html ] is one of only two moons in the Solar System [ http://space.jpl.nasa.gov ] to have an atmosphere. It has been suggested Titan might have gasoline-like lakes and an atmospheric chemistry like that [ http://www.llnl.gov/str/Macintosh.html ] found on early Earth. The Cassini spacecraft was launched in October 1997 [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] and has now traveled beyond Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap010808.html ]. |
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Ski Enceladus
| Title |
Ski Enceladus |
| Explanation |
A small inner moon of Saturn [ http://csep10.phys.utk.edu/astr161/lect/saturn/moons.html ], Enceladus is only about 500 kilometers in diameter. But the cold, distant world does reflect over 90 percent of the sunlight it receives, giving its surface about the same reflectivity as new-fallen snow. Seen here [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA00347 ] in a mosaic of Voyager [ http://vraptor.jpl.nasa.gov/voyager/ vgrsat_fs.html ] 2 images from 1981, Enceladus [ http://solarsystem.nasa.gov/features/planets/saturn/ enceladus.html ] shows a variety of surface features and very few impact craters - indicating that it is an active world even though this ice moon should have completely cooled off long ago [ http://www.sciam.com/explorations/010697sagan/ 010697sagan1.html ]. In fact the fresh, resurfaced appearance of Enceladus suggests that an internal mechanism, perhaps driven by tidal pumping, generates heat and supplies liquid water to geysers or water volcanos [ http://pirlwww.lpl.arizona.edu/HIIPS/ Cryovolcanism/ ]. Since Enceladus orbits within the tenuous outer E [ http://www.astro.spbu.ru/staff/dikarev/valery/ering.html ] ring [ http://ringmaster.arc.nasa.gov/saturn/ saturn.html#IMAGES ] of Saturn, the moon's surface may be kept snow-bright as it is continuously bombarded with icy ring particles. Eruptions [ http://www.jpl.nasa.gov/cassini/Mission/pix/ enceladus_lg.gif ] on Enceladus itself would in turn supply material to the E ring. Interplanetary [ http://www.jpl.nasa.gov/cassini/Mission/ ] ski [ http://antwrp.gsfc.nasa.gov/apod/ap990401.html ] bums take note: tiny Enceladus has only about one hundredth the surface gravity of planet Earth [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA03439 ]. |
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Jupiter's Great X-Ray Spot
| Title |
Jupiter's Great X-Ray Spot |
| Explanation |
The Solar System's largest planet, gas giant Jupiter [ http://www.windows.ucar.edu/tour/link=/jupiter/discovery.html ], is famous for its swirling Great Red Spot [ http://heritage.stsci.edu/1999/29/index.html ]. In the right hand panel above, the familiar giant planet with storm system and cloud bands [ http://antwrp.gsfc.nasa.gov/apod/ap010215.html ] is shown in an optical image from the passing Cassini spacecraft [ http://www.jpl.nasa.gov/jupiterflyby/ ]. In the left hand panel, a false-color image from the orbiting [ http://chandra.harvard.edu/about/tracking.html ] Chandra Observatory [ http://chandra.harvard.edu/about/axaf_mission.html ] presents a corresponding x-ray view of Jupiter. The Chandra image [ http://chandra.harvard.edu/photo/2002/0001/ index.html ] shows clearly, for the first time, x-ray spots and auroral x-ray emission from the poles [ http://antwrp.gsfc.nasa.gov/apod/ap001219.html ]. The x-ray spot dominating the emission from Jupiter's north pole [ http://antwrp.gsfc.nasa.gov/apod/ap010201.html ] (top) is perhaps as surprising for astronomers today as the Great Red Spot once was [ http://www.seds.org/messier/xtra/Bios/cassini.html ]. Confounding previous theories [ http://chandra.harvard.edu/press/02_releases/ press_022702.html ], the x-ray spot is too far north to be associated with heavy electrically charged particles from the vicinity [ http://xxx.lanl.gov/abs/astro-ph/0202277 ] of volcanic moon Io [ http://antwrp.gsfc.nasa.gov/apod/ap981016.html ]. Chandra data also show that the spot's x-ray [ http://chandra.harvard.edu/xray_astro/xrays.html ] emission mysteriously pulsates over a period of about 45 minutes. |
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