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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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| 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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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
| Description |
Warm Fractures on Enceladus |
| Full Description |
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 |
| Full Description |
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
| Description |
Phoebe's Radiation |
| Full Description |
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 |
| Full Description |
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
| Description |
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 |
|
Dr. Robert Goddard
| title |
Dr. Robert Goddard |
| date |
01.01.1932 |
| description |
The Goddard Space Flight Center was named in honor of Dr. Robert Goddard, a pioneer in rocket development. Dr. Goddard received patents for a multi-stage rocket and liquid propellants in 1914 and published a paper describing how to reach extreme altitudes six years later. That paper, "A Method of Reaching Extreme Altitudes," detailed methods for raising weather-recording instruments higher than what could be achieved by balloons and explained the mathematical theories of rocket propulsion. The paper, which was published by the Smithsonian Institution, also discussed the possibility of a rocket reaching the moon -- a position for which the press ridiculed Goddard. Yet several copies of the report found their way to Europe, and by 1927, the German Rocket Society was established, and the German Army began its rocket program in 1931. Goddard, meanwhile, continued his work. By 1926, he had constructed and tested the first rocket using liquid fuel. Goddard's work largely anticipated in technical detail the later German V-2 missiles, including gyroscopic control, steering by means of vanes in the jet stream of the rocket motor, gimbal-steering, power-driven fuel pumps and other devices. *Image Credit*: NASA |
|
Moon Landing Sites
| title |
Moon Landing Sites |
| description |
This image shows the locations of many spacecraft that have landed on the Moon. Green triangles are Apollo missions, yellow are NASA Surveyor missions and red are Russian Luna spacecraft. *Image Credit*: National Space Science Data Center, NASA Goddard Space Flight Center. |
|
First Far Side Photo
| title |
First Far Side Photo |
| date |
10.07.1959 |
| description |
Russia's Luna 3 spacecraft returned the first views ever of the far side of the Moon. The first image was taken at 03:30 UT on 7 October at a distance of 63,500 km after Luna 3 had passed the Moon and looked back at the sunlit far side. The last image was taken 40 minutes later from 66,700 km. A total of 29 photographs were taken, covering 70% of the far side. The photographs were very noisy and of low resolution, but many features could be recognized. This is the first image returned by Luna 3, taken by the wide-angle lens, it showed the far side of the Moon was very different from the near side, most noticeably in its lack of lunar maria (the dark areas). The right three-quarters of the disk are the far side. The dark spot at upper right is Mare Moscoviense, the dark area at lower left is Mare Smythii. The small dark circle at lower right with the white dot in the center is the crater Tsiolkovskiy and its central peak. The Moon is 3475 km in diameter and north is up in this image. A full gallery of Luna 3 photographs can be found at: http://nssdc.gsfc.nasa.gov/imgcat/html/mission_page/EM_Luna_3_page1.html *Image Credit*: NASA National Space Science Data Center |
|
Hubble Follows Rapid Changes
…
| Title |
Hubble Follows Rapid Changes in Jupiter's Aurora |
|
The Secret Lives of Galaxies
…
| Title |
The Secret Lives of Galaxies Unveiled in Deep Survey |
|
The Secret Lives of Galaxies
…
| Title |
The Secret Lives of Galaxies Unveiled in Deep Survey |
|
Spitzer and Hubble Capture E
…
| Title |
Spitzer and Hubble Capture Evolving Planetary Systems |
|
Multiple Views of the Moon
| Title |
Multiple Views of the Moon |
| Description |
On April 14, 2003, a special maneuver of the Terra [ http://terra.nasa.gov/ ] spacecraft was performed as it traversed the nightside of orbit 17672. This maneuver entailed a "backward somersault" of the spacecraft as it pitched end-over-end, allowing the normally Earth-viewing instruments to look at deep space and the waxing gibbous Moon. The purpose of this acrobatic feat is to assist in the calibration of several of Terra's instruments. Over a 16-minute interval, the lunar disk passed through the fields-of-view of all nine MISR cameras, resulting in this unique set of images. Shown here are "raw" red-band data, with no adjustments for radiometric calibration. Because the pitch rate of the spacecraft resulted in different pixel spacings in the left-right and up-down directions, the aspect ratios of the raw images have been adjusted to provide roughly circular disks. Each image is labeled with the name of the camera which acquired it. The "D" cameras are the ones which normally view the Earth at the most oblique angles, and the letters "f" and "a" denote fore- and aft-viewing orientations, respectively. "An" is the vertical-viewing (nadir) camera. Why are the "D" images the sharpest? The letters "A", "B", "C", and "D" refer to the different lens designs used on MISR, with the "D" lenses having focal lengths more than twice as large as the "A" lenses. A pixel at the center of the lunar disk subtends about 65 kilometers for the "D" cameras and about 137 kilometers for the "A" cameras. As the Moon passed into the field-of-view of each of the nine cameras, the lunar disk was always viewed "straight on", so there is no multiangular effect in these images. Familiar lunar features are clearly recognizable. The dark lunar "maria" are vast plains of basaltic lava. The feature near the upper right-hand edge of the lunar disk is Mare Crisium. Between it and image center is Mare Tranquillitatis, site of the 1969 Apollo 11 lunar landing. About halfway between image center and the left edge of the disk is the crater Copernicus, with the large Mare Imbrium to its north. Near the bottom is the crater Tycho, with bright rays of ejecta extending in many directions. Planning for this maneuver has been underway since before Terra's launch. A high school Applied Engineering Competition [ http://terra.nasa.gov/Events/Competition/ ] was also held (in partnership with the Goddard Space Flight Center's Educational Programs Office) in which students were asked to visualize the precise timing and mechanics of Terra's on-orbit calibration maneuvers. Image courtesy NASA/GSFC/LaRC/JPL, MISR Team. [ http://earthobservatory.nasa.gov/cgi-bin/redirect?http://www-misr.jpl.nasa.gov/ ] Text by David J. Diner (JPL) and Clare Averill (Acro Service Corporation/JPL). |
|
The Largest Rock Known
| Title |
The Largest Rock Known |
| Explanation |
There, that faint dot in the center - that's the largest rock known. It is larger than every known asteroid [ http://www.seds.org/nineplanets/nineplanets/asteroids.html ], moon [ http://www.solarviews.com/eng/ganymede.htm ], and comet nucleus [ http://antwrp.gsfc.nasa.gov/apod/ap961210.html ]. It is larger than any other rocky planet [ http://antwrp.gsfc.nasa.gov/apod/ap960923.html ]. (Nobody knows for sure what size rocks lie at the cores of Jovian planets [ http://quest.arc.nasa.gov/galileo/index.html ], or orbit other stars.) The Voyager [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ] 1 spacecraft took this picture [ http://nssdc.gsfc.nasa.gov/photo_gallery/caption/solar_family.txt ] in 1990 from the outer Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap980517.html ]. This rock is so large its gravity [ http://www.glenbrook.k12.il.us/gbssci/phys/Class/1DKin/U1L5b.html ] makes it nearly spherical, and holds heavy gases near its surface. Yesterday, this rock started another orbit around its parent star [ http://antwrp.gsfc.nasa.gov/apod/ap980830.html ], for roughly the 5 billionth time, spinning over 350 times during each trip. Happy Gregorian Calendar [ http://es.rice.edu/ES/humsoc/Galileo/Things/gregorian_calendar.html ] New Year to all the human inhabitants of this rock [ http://www.seds.org/billa/psc/pbd.html ] we call Earth [ http://antwrp.gsfc.nasa.gov/apod/ap990131.html ]. |
|
Super-Earths May Circle Othe
…
| Title |
Super-Earths May Circle Other Stars |
| Explanation |
Are "super-Earths" common around other star systems? Quite possibly. Unexpected evidence [ http://www.cfa.harvard.edu/press/pr0614.html ] for this came to light recently when a planet orbiting a distant star gravitationally magnified [ http://astron.berkeley.edu/~jcohn/lens.html ] the light of an even more distant star. Assuming the planet's parent star is normal red dwarf [ http://en.wikipedia.org/wiki/Red_dwarf ], the brightening is best explained if the planet is about 13 times the mass of the Earth [ http://antwrp.gsfc.nasa.gov/apod/ap030324.html ] and orbiting at the distance of the asteroid belt [ http://antwrp.gsfc.nasa.gov/apod/ap060319.html ] in our own Solar System [ http://space.jpl.nasa.gov/ ]. Given the small number of objects observed and similar determinations already obtained for other star systems, these super-Earths might be relatively common. Astronomers speculate [ http://arxiv.org/PS_cache/astro-ph/pdf/0603/0603276.pdf ] that the planet might have grown into a Jupiter-sized [ http://antwrp.gsfc.nasa.gov/apod/ap050911.html ] planet if its star system had more gas. Since the planet was not observed directly, significant uncertainty [ http://www.aip.org/history/heisenberg/p08c.htm ] remains in its defining attributes, and future research will be aimed at better understanding this intriguing system. The above drawing [ http://www.cfa.harvard.edu/press/pr0614image.html ] gives an artist's depiction of what a super-Earth orbiting a distant red dwarf [ http://imagine.gsfc.nasa.gov/docs/science/know_l2/stars.html ] star might look like, complete with a hypothetical moon [ http://antwrp.gsfc.nasa.gov/apod/ap050805.html ]. |
|
Eros Encounter Nears
| Title |
Eros Encounter Nears |
| Explanation |
After an unanticipated [ http://antwrp.gsfc.nasa.gov/apod/ap000205.html ] extra trip around the Sun, the NEAR spacecraft [ http://near.jhuapl.edu/ ] is now politely approaching [ http://near.jhuapl.edu/iod/000/index.html ] asteroid 433 [ http://near.jhuapl.edu/eros/history/too_many.html ], Eros [ http://near.jhuapl.edu/eros/history/ ], at a respectful relative speed of about 20 miles per hour. Still nearly 2,000 miles distant, NEAR will [ http://www.jhuapl.edu/public/pr/000208.htm ] close to within approximately 200 miles by February 14th - Valentine's Day. If all goes well, the spacecraft will then be captured by the gentle attraction of Eros' [ http://near.jhuapl.edu/eros/sum.html ] gravity, becoming the first artificial moon of an asteroid [ http://antwrp.gsfc.nasa.gov/apod/ap990807.html ]. While Eros is not round [ http://nearweb.jhuapl.edu/cgi-bin/ion-p?page=near_shape.html ] it is certainly not heart-shaped [ http://echo.jpl.nasa.gov/asteroids/433_Eros/eros.html ] either as seen in this series [ http://near.jhuapl.edu/iod/20000207/index.html ] of frames showing the roughly 20 x 8 x 8 mile asteroid during its 5.27 hour rotation period. Different [ http://www.seds.org/nineplanets/nineplanets/pxmisc.html#otherast ] perspectives clearly show a gouge or saddle and a large impact crater with a raised rim near the asteroid's [ http://www.boulder.swri.edu/~cchapman/finderos.html ] narrow waist. The frames were recorded by the NEAR spacecraft's multi-spectral imager [ http://near.jhuapl.edu/instruments/ ] on February 4th from a range of 4,600 miles. |
|
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 ]. |
|
Stereo Saturn
| Title |
Stereo Saturn |
| Explanation |
Get out your red/blue glasses [ http://img.arc.nasa.gov/archive/desert96/redblue.html ] and launch [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] yourself into this stereo [ http://cass.jsc.nasa.gov/research/stereo_atlas/SS3D.HTM ] picture of Saturn! The picture is actually composed from two images recorded weeks apart by the Voyager 2 spacecraft [ http://vraptor.jpl.nasa.gov/voyager/voyager_fs.html ] during its visit to [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ] the Saturnian System in August of 1981. Traveling at about 35,000 miles per hour, the spacecraft's changing viewpoint from one image to the next produced this exaggerated but pleasing stereo effect [ http://antwrp.gsfc.nasa.gov/apod/ap970404.html ]. Saturn is the second largest planet [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/saturn.html ] in the Solar System, after Jupiter. Its spectacular ring system [ http://ringmaster.arc.nasa.gov/saturn/saturn.html ] is so wide that it would span the space between the Earth and Moon. Although they look solid here, Saturn's [ http://antwrp.gsfc.nasa.gov/apod/ap000129.html ] rings consist of individually orbiting bits of ice and rock ranging in size from grains of sand to barn-sized boulders. |
|
Southwest Mercury
| Title |
Southwest Mercury |
| Explanation |
The planet Mercury resembles a moon. Mercury [ http://www.seds.org/nineplanets/nineplanets/mercury.html ]'s old surface is heavily cratered [ http://liftoff.msfc.nasa.gov/Academy/SPACE/SolarSystem/Meteors/Craters.html ] like many moons. Mercury [ http://www.solarviews.com/eng/mercury.htm ] is larger than most moons but smaller than Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap990806.html ]'s moon Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap990304.html ] and Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap960717.html ]'s moon Titan [ http://antwrp.gsfc.nasa.gov/apod/ap990207.html ]. Mercury is much denser and more massive than any moon, though, because it is made mostly of iron. In fact, the Earth [ http://antwrp.gsfc.nasa.gov/apod/ap990131.html ] is the only planet more dense. A visitor to Mercury's surface [ http://antwrp.gsfc.nasa.gov/apod/ap960121.html ] would see some strange sights. Because Mercury [ http://www.oulu.fi/~spaceweb/textbook/mercury.html ] rotates exactly three times every two orbits around the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap951004.html ], and because Mercury [ http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-mercury.html ]'s orbit is so elliptical, a visitor to Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap990102.html ] might see the Sun [ http://antwrp.gsfc.nasa.gov/htmltest/gifcity/interv.html ] rise, stop in the sky, go back toward the rising horizon [ http://antwrp.gsfc.nasa.gov/apod/ap990619.html ], stop again, and then set quickly over the other horizon. From Earth [ http://antwrp.gsfc.nasa.gov/apod/ap980530.html ], Mercury's proximity to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap981212.html ] cause it to be visible only for a short time just after sunset or just before sunrise. |
|
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/ ]. |
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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. |
|
Animation of Asteroids Passi
…
| Title |
Animation of Asteroids Passing Near Earth |
| Explanation |
How often does an asteroid whiz by the Earth? The above time-lapse animation [ http://cfa-www.harvard.edu/iau/Animations/Animations.html ] follows the orbit of the Earth around the Sun for two months in 2002 as numerous asteroids [ http://en.wikipedia.org/wiki/Asteroids ], also known as minor planets [ http://en.wikipedia.org/wiki/Minor_planet ], approach and pass by. Some asteroids appear out of nowhere [ http://antwrp.gsfc.nasa.gov/apod/ap041001.html ] as they are plotted only when they were discovered. Most asteroids plotted were discovered only [ http://antwrp.gsfc.nasa.gov/apod/ap040322.html ] during the previous year. Although none of the plotted objects came inside the orbit of our Moon, our Solar System is filled with objects [ http://antwrp.gsfc.nasa.gov/apod/ap050417.html ] as small as bits of sand, usually left by a comet, that appear as meteors as they streak into the Earth's atmosphere every day. The only objects displayed are those visible from Earth [ http://antwrp.gsfc.nasa.gov/apod/ap050102.html ] closer than 20 million kilometers, color coded by three-dimensional distance. In comparison, the Earth is a relatively small target having a radius of about 6,400 kilometers. One significant research area [ http://pan-starrs.ifa.hawaii.edu/public/asteroid-threat/asteroid_threat.html ] in modern astronomy involves trying to find the majority of asteroids that could pose a future collision threat [ http://neo.jpl.nasa.gov/risk/ ] with Earth. |
|
Zal Patera on Jupiter's Moon
…
| Title |
Zal Patera on Jupiter's Moon Io |
| Explanation |
The Galileo orbiter [ http://www.jpl.nasa.gov/galileo/mission.html ]'s flyby of Io [ http://www.seds.org/nineplanets/nineplanets/io.html ] last November captured an unusual part of Jupiter [ http://antwrp.gsfc.nasa.gov/apod/jupiter.html ]'s volcanic moon. From 26,000 kilometers away, Zal Patera [ http://wwwflag.wr.usgs.gov/USGSFlag/Space/nomen/append5.html ] was found to be a cauldron of flowing lava [ http://antwrp.gsfc.nasa.gov/apod/ap991220.html ], gaseous vents [ http://antwrp.gsfc.nasa.gov/apod/ap970428.html ], and tremendous peaks [ http://antwrp.gsfc.nasa.gov/apod/ap960805.html ]. Red lava can be seen in the above picture [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02527 ] erupting along the base of the volcanic caldera, while cooling black lava lines the edge of a volcanic plateau. Shadow lengths indicate that the top of Zal Patera [ http://antwrp.gsfc.nasa.gov/apod/ap990513.html ] towers nearly 5 kilometers over Io [ http://galileo.jpl.nasa.gov/moons/io.html ]'s molten surface. Galileo zoomed past Io again last month [ http://galileo.jpl.nasa.gov/news/status/status000225.html ], and has begun beaming back images taken only 200 kilometers over Io's surface [ http://antwrp.gsfc.nasa.gov/apod/ap990920.html ]. |
|
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. |
|
Descent Panorama of Saturn's
…
| Title |
Descent Panorama of Saturn's Titan |
| Explanation |
You're the first spacecraft ever to descend to Titan -- what do you see? Immediately after the Huygen's probe [ http://en.wikipedia.org/wiki/Huygens_probe ] pierced the cloud deck of Saturn [ http://en.wikipedia.org/wiki/Saturn_%28planet%29 ]'s moon Titan [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search?titan ] last January, it took a unique series of pictures of one of the Solar System [ http://www.windows.ucar.edu/our_solar_system/solar_system.html ]'s most mysterious moon's. Those pictures have recently been digitally stitched together to create spectacular panoramas and a dramatic descent movie [ http://photojournal.jpl.nasa.gov/catalog/PIA08117 ]. Pictured above [ http://photojournal.jpl.nasa.gov/catalog/PIA08114 ] is a panoramic fisheye view Huygen's obtained from about five kilometers above Titan's surface [ http://antwrp.gsfc.nasa.gov/apod/ap050117.html ]. The digital projection makes the local surface, mostly flat, appear as a ball, but allows one to see in all directions. Huygen's eventual landing site [ http://antwrp.gsfc.nasa.gov/apod/ap050518.html ] was in the large dark area below, just right of the center. This relatively featureless, dark, sandy basin appears to be surrounded by light colored hills to the right and a landscape fractured by streambeds and canyons [ http://antwrp.gsfc.nasa.gov/apod/ap050124.html ] above. Recent evidence [ http://uanews.org/cgi-bin/WebObjects/UANews.woa/16/wa/MainStoryDetails?ArticleID=12614 ] indicates that Titan's lakebeds and streambeds are usually dry but sometimes filled with a flashflood of liquid methane [ http://en.wikipedia.org/wiki/Methane ] from rare torrents of methane rain [ http://www.astrobio.net/news/article1413.html ]. |
|
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. |
|
Mysterious Pluto and Charon
| Title |
Mysterious Pluto and Charon |
| Explanation |
Pluto [ http://www.seds.org/nineplanets/nineplanets/pluto.html ] is the only planet in our Solar System [ http://www.fourmilab.ch/solar/solar.html ] remaining unphotographed by a passing spacecraft. Distant Pluto [ http://www.hawastsoc.org/solar/eng/pluto.htm ] and its moon Charon [ http://www.seds.org/nineplanets/nineplanets/pluto.html#charon ] therefore remain somewhat mysterious. In addition to direct imaging [ http://antwrp.gsfc.nasa.gov/apod/ap960311.html ] by the Hubble Space Telescope [ http://www.stsci.edu/hst/ ], careful tracking of brightness changes that occur as each object eclipses the other have allowed astronomers to build up the above black & white surface maps [ http://www.lowell.edu/users/buie/pluto/plutomap1.html ]. These maps depict the face of Pluto [ http://antwrp.gsfc.nasa.gov/apod/ap990213.html ] (left) that always faces Charon, and the face of Charon that always faces away from Pluto [ http://antwrp.gsfc.nasa.gov/apod/ap960212.html ]. The rectangular pixels [ http://machaut.uchicago.edu/cgi-bin/WEDT1.sh?word=pixel ] are an artifact of the mapping software. The Pluto-Kuiper Express [ http://www.jpl.nasa.gov/ice_fire//pkexprss.htm ] mission is tentatively planned for launch [ http://www.jpl.nasa.gov/ice_fire//mstats.htm ] in 2004 and might encounter Pluto as early as 2012. |
|
Europa: Ice Line
| Title |
Europa: Ice Line |
| Explanation |
This bright white swath cutting across the surface of icy Jovian moon Europa [ http://galileo.jpl.nasa.gov/moons/europa.html ] is known as Agenor Linea [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA00877 ]. In all about 1000 kilometers long and 5 kilometers wide, only a section is pictured here [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA01647 ] as part of a combined color and black and white image based on data from the Galileo spacecraft. Most linear features on Europa [ http://www.jpl.nasa.gov:80/galileo/europa/fact.html ] are dark in color but Agenor Linea is uniquely bright for unknown reasons. Also unknown is the origin of the reddish material along the sides. While these and other details of Europa's [ http://www.jpl.nasa.gov:80/galileo/news8.html ] surface formations remain mysterious, the general results of Galileo's exploration of Europa have supported the idea that an ocean of liquid water lies beneath [ http://photojournal.jpl.nasa.gov/ cgi-bin/PIAGenCatalogPage.pl?PIA01669 ] the cracked and frozen crust. An extraterrestrial liquid ocean [ http://science.nasa.gov/newhome/headlines/ast05mar98_1.htm ] holds out the tantalizing possibility [ http://quest.arc.nasa.gov/galileo/features/life.html ] of life. |
|
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. |
|
Calderas And Cliffs Near Io'
…
| Title |
Calderas And Cliffs Near Io's South Pole |
| Explanation |
Braving intense radiation [ http://www-spof.gsfc.nasa.gov/Education/Iradbelt.html ] belts [ http://www-spof.gsfc.nasa.gov/Education/wotherms.html ], the Galileo spacecraft once again [ http://galileo.jpl.nasa.gov/news/status/ status000222.html ] flew past the surface of Jupiter's moon Io [ http://sse.jpl.nasa.gov/features/planets/ jupiter/io.html ] (sounds like EYE-oh [ http://spaceplace.jpl.nasa.gov/gll_io_fact.htm ]) on February 22. Combining high resolution black and white images from that flyby with color data recorded last summer has resulted in this dramatic view [ http://photojournal.jpl.nasa.gov/ cgi-bin/PIAGenCatalogPage.pl?PIA02534 ] of a region near the volcanic moon's south pole. An active and alien landscape, the bright white areas are likely due to sulfur dioxide frost and seem to be concentrated near ridges and cliffs. The three ominous black spots, each about 6-12 miles across, are volcanic craters or calderas [ http://volcano.und.nodak.edu/vwdocs/vwlessons/lessons/ Hot_Spot/Hot_Spot10.html ] covered with recent dark lava. A sinuous channel connects the lower left caldera with a yellowish lava flow. Io is small, but its continuous [ http://www-a.jpl.nasa.gov/galileo/ganymede/ 122096.html ] activity is driven by the drastic tides [ http://co-ops.nos.noaa.gov/restles1.html ] induced by Jupiter [ http://sse.jpl.nasa.gov/features/planets/ jupiter/jupiter.html ] and the other Jovian moons. It is estimated that the resulting volcanism [ http://volcano.und.edu/vwdocs/planet_volcano/Io/ Overview.html ] completely resurfaces Io [ http://antwrp.gsfc.nasa.gov/apod/ap970321.html ] every million years. |
|
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. |
|
Planets In The Sun
| Title |
Planets In The Sun |
| Explanation |
Today [ http://science.nasa.gov/headlines/y2000/ast02may_1.htm ], all five naked-eye planets [ http://www.seds.org/nineplanets/nineplanets/ ] (Mercury, Venus, Mars, Jupiter, Saturn) plus the Moon and the Sun [ http://helios.gsfc.nasa.gov/ sun.html ] will at least approximately line-up. As viewed [ http://drumright.ossm.edu/astronomy/conjunctions.html ] from planet Earth, they will be clustered within about 26 degrees, the closest alignment for all these celestial bodies [ http://science.nasa.gov/headlines/y2000/ ast30mar_1m.htm#alignments ] since February 1962, when there was a solar eclipse [ http://antwrp.gsfc.nasa.gov/apod/ap990818.html ]! Such planetary alignments [ http://www.griffithobs.org/SkyAlignments.html ] are not dangerous, except of course that the Sun might hurt your eyes when you look at it [ http://antwrp.gsfc.nasa.gov/apod/ap981212.html ]. So it might be easier [ http://sohowww.nascom.nasa.gov/hotshots/ ] to appreciate today's solar system [ http://space.jpl.nasa.gov/ ] spectacle if |
|
Ganymede: The Largest Moon i
…
| Title |
Ganymede: The Largest Moon in the Solar System |
| Explanation |
If Ganymede orbited the Sun, it would be considered a planet. The reason is that Jupiter [ http://galileo.jpl.nasa.gov/jupiter/jupiter.html ]'s moon Ganymede [ http://www.seds.org/nineplanets/nineplanets/ganymede.html ] is not only the largest moon in the Solar System [ http://www.seds.org/nineplanets/nineplanets/datamax.html ], it is larger than planets Mercury [ http://www.seds.org/nineplanets/nineplanets/mercury.html ] and Pluto [ http://dosxx.colorado.edu/plutohome.html ]. The robot spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/overview.html ] currently orbiting Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ] has been able to zoom by Ganymede [ http://www.solarviews.com/eng/ganymede.htm ] several times and snap many close-up pictures. Ganymede, shown above [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA00716 ] in its natural colors, sports a large oval dark region known as Galileo Regio [ http://www.jpl.nasa.gov/galileo/ganymede/121896.html ]. In general, the dark regions on Ganymede [ http://sse.jpl.nasa.gov/features/planets/jupiter/ganymede.html ] are heavily cratered, implying they are very old, while the light regions are younger and dominated by unusual grooves [ http://antwrp.gsfc.nasa.gov/apod/ap960711.html ]. The origin of the grooves is still under investigation [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998Icar..135..317P ]. |
|
The Comet and the Galaxy
| Title |
The Comet and the Galaxy |
| Explanation |
The Moon almost ruined this photograph. During late March and early April 1997, Comet Hale-Bopp [ http://www.jpl.nasa.gov/comet/ ] passed nearly in front of the Andromeda Galaxy [ http://antwrp.gsfc.nasa.gov/apod/ap040718.html ]. Here the Great Comet of 1997 [ http://cometography.com/lcomets/1995o1.html ] and the Great Galaxy in Andromeda [ http://www.seds.org/messier/m/m031.html ] were photographed together [ http://antwrp.gsfc.nasa.gov/apod/ap970401.html ] on 1997 March 24th. The problem was the brightness of the Moon [ http://antwrp.gsfc.nasa.gov/apod/ap970924.html ]. The Moon [ http://www.seds.org/nineplanets/nineplanets/luna.html ] was full that night and so bright that long exposures meant to capture the tails of Hale-Bopp [ http://antwrp.gsfc.nasa.gov/apod/ap970416.html ] and the disk of M31 [ http://antwrp.gsfc.nasa.gov/apod/ap961011.html ] would capture instead only moonlight reflected off the Earth's atmosphere. By the time the Moon would set, this opportunity would be gone. That's why this picture was taken during a total lunar eclipse [ http://antwrp.gsfc.nasa.gov/apod/ap960926.html ]. |
|
Up Close to Jupiter's Moon I
…
| Title |
Up Close to Jupiter's Moon Io |
| Explanation |
Above is the highest resolution photograph [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02556 ] yet taken of the Solar System [ http://www.seds.org/nineplanets/nineplanets/overview.html ]'s strangest moon. The surface of Jupiter [ http://www.solarviews.com/eng/jupiter.htm ]'s moon Io [ http://galileo.jpl.nasa.gov/moons/io.html ] is home to violent volcanoes [ http://antwrp.gsfc.nasa.gov/apod/ap000606.html ] that are so active they turn the entire moon inside out. The above photograph [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02556 ] shows a region four kilometers across and resolves features only five meters [ http://www.twenj.com/measures.htm ] across. Many revealed details are not well understood. In general, the bright areas are higher terrain than the darker areas, but some areas of the surface appear eroded [ http://www.qub.ac.uk/geosci/teaching/postgrad/workshop1/erosion1.html ] by an unknown process. Although the parts of Io's surface [ http://antwrp.gsfc.nasa.gov/apod/ap970321.html ] near erupting volcanoes are hot enough to melt rock, most of Io [ http://antwrp.gsfc.nasa.gov/apod/ap990920.html ] has cooled well below the freezing point of water [ http://www.nyu.edu/pages/mathmol/modules/water/info_water.html ]. The robot spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/overview.html ] during its most recent flyby [ http://galileo.jpl.nasa.gov/news/release/press000531.html ] of Io [ http://www.seds.org/nineplanets/nineplanets/io.html ] took the above image in 2000 February. |
|
A Continuous Eruption on Jup
…
| Title |
A Continuous Eruption on Jupiter's Moon Io |
| Explanation |
A volcano on Jupiter's moon Io [ http://www.seds.org/nineplanets/nineplanets/io.html ] has been photographed recently during an ongoing eruption. Hot glowing lava is visible on the left on this representative-color image [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02550 ]. A glowing landscape of plateaus and valleys covered in sulfur [ http://pearl1.lanl.gov/periodic/elements/16.html ] and silicate rock [ http://windows.ivv.nasa.gov/cgi-bin/tour_def/glossary/silicate_rock.html ] surrounds the active volcano [ http://volcano.und.nodak.edu/vwdocs/planet_volcano/Io/Overview.html ]. Many features including several of the dark spots [ http://antwrp.gsfc.nasa.gov/apod/ap971110.html ] have evolved between February 2000, when the robot spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/spacecraft.html ] currently orbiting Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ] took this picture, and November 1999. Io [ http://cass.jsc.nasa.gov/pub/research/outerp/io.html ] is slightly larger than Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap991108.html ] and is the closest large moon to Jupiter [ http://galileo.jpl.nasa.gov/jupiter/jupiter.html ]. The above image [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02550 ] shows a region about 250 kilometers across. How the internal structure of Io [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1990Icar...85..309R ] creates these active volcanoes [ http://antwrp.gsfc.nasa.gov/apod/ap961027.html ] remains under investigation. |
|
Crater On Ice
| Title |
Crater On Ice |
| Explanation |
Impact craters are common on Earth's moon [ http://antwrp.gsfc.nasa.gov/apod/ap990326.html ] but on Jupiter's large ice moon Europa [ http://sse.jpl.nasa.gov/features/planets/jupiter/ europa.html ], they are very rare. Over time, both bodies have been subjected to an intense pounding [ http://antwrp.gsfc.nasa.gov/apod/ap990610.html ] by the solar system's formative debris [ http://www.jhuapl.edu/public/pr/000530.htm ], but geological activity on Europa's surface seems to have erased most of these impact scars. This false-color infrared image [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA02561 ] from the Galileo spacecraft's NIMS instrument [ http://jumpy.igpp.ucla.edu/~nims/ ] shows a newly discovered crater on Europa as a light red ring feature near center surrounding a dark core. For scale, the dark core is about 29 kilometers in diameter. Only seven comparably [ http://antwrp.gsfc.nasa.gov/apod/ap970417.html ] large craters have now been identified on Europa's surface. Red colors in the image represent a relatively pure water ice [ http://www.glacier.rice.edu/invitation/1_icetypes.html ] composition while blue colors indicate that other minerals are present. The crater's central dark area may contain the remnants of the impacting body. The icy crust of Europa [ http://galileo.jpl.nasa.gov/moons/europa.html ] is of great interest, as evidence mounts [ http://galileo.jpl.nasa.gov/news/release/ press000110.html ] that it covers an ocean of liquid water, possibly providing suitable conditions for life. |
|
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. |
|
Other Worlds and HD 38529
| Title |
Other Worlds and HD 38529 |
| Explanation |
After the latest round of discovery announcements [ http://www.iau.org/ga24press/ ], the list of known worlds of distant suns [ http://www.spaceart.org/lcook/extrasol.html ] has grown to 50 [ http://www.spaceref.com/news/viewnews.html?id=200 ]. While extrasolar planet [ http://exoplanets.org/ ] discoveries are [ http://obswww.unige.ch/~udry/planet/planet.html ] sure to continue, none - so far [ http://sim.jpl.nasa.gov/ ] - points clearly to another planetary system like our own [ http://antwrp.gsfc.nasa.gov/apod/ap991229.html ]. Take, for example, the newly discovered parent [ http://antwrp.gsfc.nasa.gov/apod/ap990611.html ] star HD38529 [ http://www.obspm.fr/encycl/HD38529.html ]. Shining in Earth's night sky at 6th magnitude, this sun-like star lies 137 light-years away in the constellation Orion [ http://aibn47.astro.uni-bonn.de/~gallery/constellations/orion/ main.html ]. Like most of the known extrasolar planets [ http://www.obspm.fr/encycl/encycl.html ], HD38529's planet was discovered by detecting the telltale Doppler wobble [ http://exoplanets.org/doppler.html ] in the parent star's spectrum. The data reveal that this planet orbits once every 14.3 days at an average of only 0.13 times the Earth-Sun distance and has a minimum of 0.77 Jupiter masses (about 240 Earth masses). There is even evidence [ http://www.iau.org/ga24press/pr000807_3.html#1 ] in the wobble data that HD38529, and other stars with one known planet have additional massive planets orbiting them. In this dramatic artist's vision, HD38529 and its newfound world are viewed from the moon of another massive ringed planet [ http://antwrp.gsfc.nasa.gov/apod/ap000330.html ] orbiting farther out. The ringed planet's moon is imagined to have a thin atmosphere and a surface covered with icy sheets and ridges similar to those found on Jupiter's moon Europa [ http://galileo.jpl.nasa.gov/moons/europa.html ]. |
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