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Earth and Moon of Goddard Space Flight Center (GSFC) and Jet Propulsion Laboratory (JPL)
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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 Temperature Maps
| Description |
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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Hubble Follows Rapid Changes
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Hubble Follows Rapid Changes in Jupiter's Aurora |
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Spitzer and Hubble Capture E
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| Title |
Spitzer and Hubble Capture Evolving Planetary Systems |
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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). |
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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 ]. |
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Super-Earths May Circle Othe
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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 ]. |
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Natural Saturn On The Cassin
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| 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 ]. |
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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. |
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Southwest Mercury
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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. |
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Sky and Planets
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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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Animation of Asteroids Passi
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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. |
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Venus, Moon, and Neighbors
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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. |
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Saturn in Blue and Gold
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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. |
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Ancient Craters on Saturn's
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| 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. |
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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 |
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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 ]. |
|
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. |
|
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 ]. |
|
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 ]. |
|
Folding Europa
| Title |
Folding Europa |
| Explanation |
Astypalaea Linea [ http://wwwflag.wr.usgs.gov/USGSFlag/Space/nomen/jupiter/ euroTOC.html ] on Jovian [ http://cfa-www.harvard.edu/iau/pressinfo/S1999J1.html ] ice moon Europa [ http://www.seds.org/nineplanets/nineplanets/ europa.html ] is the broad smooth region running through these images [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA02960 ] recorded by the Galileo spacecraft in 1998. The pictures are different computer processed versions of the same mosaic -- on the left, small scale details have been enhanced while on the right, large scale features are emphasized. In both versions, the bold criss-crossing ridges [ http://antwrp.gsfc.nasa.gov/apod/ap981215.html ] believed to result from the upwelling of new material through cracks in the surface ice are apparent. But more easily seen on the right are recently recognized [ http://www.jhuapl.edu/public/pr/000810.htm ] gentle rises and dips, about 15 kilometers across, which likely formed as the icy surface was compressed by the addition of the new material. Further evidence [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query? bibcode=2000LPI....31.1182P&db_key=AST&high=3899d8d98211881 ] that stress is folding Europa's [ http://galileo.jpl.nasa.gov/moons/europa.html ] surface is offered by the presence of smaller cracks and wrinkles more easily seen on the left. These span the width of the broad swells suggestive of anticlines and synclines [ http://www.educ.uvic.ca/Faculty/jtinney/earth%20science/ ESMain.html#fold ] familiar to geologists on planet Earth [ http://antwrp.gsfc.nasa.gov/apod/ap000420.html ]. Though ice covered [ http://spacescience.com/headlines/y2000/ ast22aug_1.htm ], the surface of Europa is thought to be geologically active, riding over a substantial ocean [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query? bibcode=1998Natur.391..363C&db_key=AST&high=3899d8d98211557 ] of liquid water. |
|
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. |
|
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. |
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North Pole Below
| Title |
North Pole Below |
| Explanation |
Orbiting over the north pole of planet Earth [ http://earthobservatory.nasa.gov/ ] on May 5, the MODIS instrument on-board the Terra spacecraft [ http://terra.nasa.gov/ ], recorded this view of the ice cap [ http://earthobservatory.nasa.gov/Newsroom/NewImages/ images.php3?img_id=4193 ] 700 kilometers below. A radial grid centered on the pole is shown on top of the approximately true color image where each pixel covers about one square kilometer. Frozen sea ice [ http://www.natice.noaa.gov/ ] appears whitish while open water or newly refrozen ice looks black. An impressive criss-crossing network of cracks in ice shifting above a liquid water ocean is visible, traced by the meandering dark lines. In fact, the dark network of cracks in the sea ice [ http://southport.jpl.nasa.gov/polar/iceinfo.html ] is reminiscent of another world in our solar system which may also harbor a liquid water ocean -- Jupiter's ice moon [ http://antwrp.gsfc.nasa.gov/apod/ap960813.html ] Europa [ http://galileo.jpl.nasa.gov/moons/europa.html ]. |
|
Eclipse Moon Trail
| Title |
Eclipse Moon Trail |
| Explanation |
Tonight, Friday the 13th, October's big, bright, beautiful full Moon [ http://antwrp.gsfc.nasa.gov/apod/ap000113.html ] will be in the sky, rising as the sun sets. A time exposure of this evening's full Moon would show a brilliant circular arc or Moon trail tracing its celestial path. In fact, this single [ http://pages.prodigy.net/pam.orman/joemoon/ MoonPlanets_000120_2.html ], four hour long exposure from the evening of January 20 shows a full Moon trailing through hazy skies above [ http://pages.prodigy.net/pam.orman/ JoeGallery.html ] Phoenix, Arizona, USA. Of course, the picture also shows something you won't see tonight -- a total lunar eclipse [ http://www.mreclipse.com/Special/LEprimer.html ]. A lunar eclipse is caused when the full moon enters Earth's shadow [ http://image.gsfc.nasa.gov/poetry/ask/q2806.html ] and as the eclipsed Moon's light grows steadily fainter, the Moon trail becomes narrow and dim. The total eclipse phase, when the Moon passes completely within Earth's shadow [ http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=3&vbody=103& month=1&day=21¢ury=20&decade=0&year=0&hour=04&minute=0& rfov=30&fovmul=-1&bfov=30 ], occurs near the middle of this Moon trail arc [ http://antwrp.gsfc.nasa.gov/apod/ap000905.html ]. But even during totality, the Moon trail is visible and noticeably red. Normally illuminated by sunlight which falls directly on its surface, during a total lunar eclipse the Moon is still illuminated [ http://antwrp.gsfc.nasa.gov/apod/ap991108.html ] by sunlight filtered and refracted through Earth's atmosphere. The refracted light lends the eclipsed Moon [ http://www.mreclipse.com/ ] a dim and reddish appearance. |
|
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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Double Asteroid 90 Antiope
| Title |
Double Asteroid 90 Antiope |
| Explanation |
This eight-frame animation is based on the first ever images [ http://www.boulder.swri.edu/~merline/press/ ] of a double asteroid [ http://www.boulder.swri.edu/~merline/press/release.txt ]! Formerly thought to be a single enormous chunk of rock, asteroid 90 Antiope [ http://cfa-www.harvard.edu/iau/lists/ NumberedMPs00001.html ] resides in the solar system's [ http://space.jpl.nasa.gov/ ] main asteroid belt [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ asteroids.html ] between Mars and Jupiter. Now, these premier images reveal Antiope to actually consist of two 50 mile wide asteroids separated by about 100 miles. Like weights on each end of an elastic string, the pair mutually orbit [ http://hyperphysics.phy-astr.gsu.edu/hbase/ orbv.html#bo ] their center of mass, or balance point in the space between them, once every 16.5 hours. Binary asteroids and asteroids with moons [ http://antwrp.gsfc.nasa.gov/apod/ap991014.html ] are believed to be rare, but observations of their orbits allow a direct determination of asteroid masses and densities. Surprisingly, Antiope and known [ http://www.cfht.hawaii.edu/News/PR_001026/ ] asteroid-moon [ http://antwrp.gsfc.nasa.gov/apod/ap990807.html ] systems are found to have densities closer to ice than rock, despite their relatively dark and unreflective surfaces. These sharp images were made at the Keck Observatory atop the Hawaiian volcano Mauna Kea using newly developed adaptive optics [ http://www.mtwilson.edu/Science/ AdapOpt/Overview/ ] technology to overcome the blurring effect [ http://antwrp.gsfc.nasa.gov/apod/ap000725.html ] of Earth's atmosphere. |
|
A Year of Extraterrestrial F
…
| Title |
A Year of Extraterrestrial Fountains and Flows |
| Explanation |
The past year was extraordinary for the discovery of extraterrestrial fountains and flows -- some offering new potential in the search for liquid water and the origin of life beyond planet Earth.. Increased evidence was uncovered that fountains [ http://antwrp.gsfc.nasa.gov/apod/ap060608.html ] spurt not only from Saturn's moon Enceladus [ http://antwrp.gsfc.nasa.gov/apod/ap060310.html ], but from the dunes of Mars [ http://antwrp.gsfc.nasa.gov/apod/ap060823.html ] as well. Lakes were found on Saturn's moon Titan [ http://antwrp.gsfc.nasa.gov/apod/ap060731.html ], and the residual of a flowing liquid was discovered on the walls of Martian craters [ http://antwrp.gsfc.nasa.gov/apod/ap061212.html ]. The diverse Solar System [ http://en.wikipedia.org/wiki/Solar_system ] fluidity may involve forms of slushy water-ice, methane [ http://scifun.chem.wisc.edu/chemweek/methane/methane.html ], or sublimating [ http://en.wikipedia.org/wiki/ Sublimation_%28physics%29 ] carbon dioxide [ http://scifun.chem.wisc.edu/chemweek/CO2/CO2.html ]. Pictured above [ http://antwrp.gsfc.nasa.gov/apod/ap061231.html http://photojournal.jpl.nasa.gov/catalog/PIA09028 ], the light-colored path below the image center is hypothesized to have been created sometime in just the past few years by liquid water flowing [ http://www.nasa.gov/mission_pages/mars/news/mgs-20061206.html ] across the surface of Mars [ http://antwrp.gsfc.nasa.gov/apod/mars.html ]. |
|
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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Solar Eclipse from the Moon
| Title |
Solar Eclipse from the Moon |
| Explanation |
Parts of Saturday's (March 3) lunar eclipse [ http://sunearth.gsfc.nasa.gov/eclipse/OH/OH2007.html ] will be widely visible. For example, skywatchers [ http://www.xs4all.nl/~carlkop/maaneclips2007/ leclips2007.html ] in Europe, Africa, and western Asia will be able to see the entire spectacle of the Moon gliding through Earth's shadow, but in eastern North America the Moon will rise already in its total eclipse phase [ http://www.mreclipse.com/Special/LEprimer.html ]. Of course if you traveled to the Moon's near side [ http://science.nasa.gov/headlines/y2007/ 12feb_lunareclipse.htm ], you could see the same event as a solar eclipse, with the disk of our fair planet Earth [ http://earthobservatory.nasa.gov/Newsroom/BlueMarble/ ] completely blocking out the Sun. For a moon-based observer's view, graphic artist Hana Gartstein (Haifa, Israel [ http://maps.google.com/maps?f=q&hl=en&q=haifa,+israel &layer=&ie=UTF8&om=1&z=7&ll=33.027088,34.865112 &spn=6.83228,13.886719&t=k ]) offers this composite illustration. In the cropped version of her picture, an Apollo 17 [ http://antwrp.gsfc.nasa.gov/apod/ap051210.html ] image of Earth is surrounded with a red-tinted haze as sunlight streams [ http://antwrp.gsfc.nasa.gov/apod/ap031121.html ] through the planet's dusty atmosphere. Earth's night [ http://antwrp.gsfc.nasa.gov/apod/ap050611.html ] side remains faintly visible, still illuminated by the dark, reddened Moon, but the disk of the Earth would appear almost four times the size of the Sun's disk, so the faint corona surrounding the Sun would be largely obscured. At the upper left, the Sun itself [ http://antwrp.gsfc.nasa.gov/apod/ap060330.html ] is just disappearing [ http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=399&vbody=301 &month=3&day=3&year=2007&hour=22&minute=05&rfov=2 &fovmul=-1&bfov=30&porbs=1&showsc=1 ] behind the Earth's limb. |
|
Oceans Under Jupiter's Moon
…
| Title |
Oceans Under Jupiter's Moon Ganymede? |
| Explanation |
The search for extraterrestrial [ http://www.seti.org/ ] life came back into our own Solar System [ http://www.seds.org/nineplanets/nineplanets/overview.html ] last week with the announcement [ http://www.jpl.nasa.gov/releases/2000/aguganymederoundup.html ] that there may be liquid oceans under the surface of Jupiter [ http://antwrp.gsfc.nasa.gov/apod/jupiter.html ]'s moon Ganymede [ http://www.jpl.nasa.gov/galileo/moons/ganymede.html ]. Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap000620.html ] now joins Callisto [ http://www.jpl.nasa.gov/galileo/news32.html ] and Europa [ http://www.jpl.nasa.gov/galileo/moons/europa.html ] as moons of Jupiter [ http://www.solarviews.com/eng/jupiter.htm ] that may harbor seas of liquid water under layers of surface ice [ http://antwrp.gsfc.nasa.gov/apod/ap980722.html ]. The ocean hypothesis surfaced as an explanation for Ganymede's unusually strong magnetic field [ http://www.igpp.ucla.edu/galileo/doc/n384/text.htm ]. Ganymede, the largest moon in the Solar System, also has the largest measured magnetic field [ http://www-spof.gsfc.nasa.gov/Education/Imagnet.html ] of any moon. Some exobiologists [ http://exobiology.nasa.gov/ssx/exobiology.html ] hypothesize that life may be able to emerge [ http://www.etext.org/Zines/Quanta/life.html ] in such an ocean, much as it did in the oceans of ancient Earth [ http://wwwcatsic.ucsc.edu/~eart1/Notes/Lec1.html ]. Above [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02583 ], a frame from a computer simulation [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenDownloadOpts.pl?PIA02583 ] shows what it would look like to fly over [ http://antwrp.gsfc.nasa.gov/apod/ap961025.html ] the surface of Ganymede, as extrapolated from photographs of the grooved moon [ http://antwrp.gsfc.nasa.gov/apod/ap960711.html ] taken by the robot spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/mission.html ] currently orbiting Jupiter. |
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Degas Ray Crater on Mercury
| Title |
Degas Ray Crater on Mercury |
| Explanation |
Like the Earth's Moon, Mercury is [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/mercuryfact.html ] scarred with craters testifying to an intense bombardment during the early history [ http://antwrp.gsfc.nasa.gov/apod/ap990326.html ] of the Solar System. In 1974, the Mariner 10 [ http://pds.jpl.nasa.gov/planets/welcome/m10.htm ] spacecraft surveyed this innermost planet [ http://nssdc.gsfc.nasa.gov/imgcat/html/mission_page/ MC_Mariner_10_page1.html ] up close, producing the only detailed images of its tortured surface. In the above mosaic [ http://nssdc.gsfc.nasa.gov/imgcat/html/object_page/ m10_aom_3_e.html ] the bright rays emanating from the 45 kilometer wide Degas crater almost appear to be painted on [ http://sunsite.unc.edu/wm/paint/auth/degas/ ]. The rays consist of light colored material blasted out during the crater's formation. Craters [ http://www.lpi.usra.edu/expmoon/science/ craterstructure.html ] older than Degas are covered by the ray material while younger craters are seen superimposed on the rays. Mercury's [ http://www.seds.org/nineplanets/nineplanets/ mercury.html ] gravity and density are about [ http://www.whfreeman.com/ENVIRONMENTALGEOLOGY/EXMOD36/ PLANET.HTM ] twice that of Earth's [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/ planet_table_ratio.html ] Moon so such bright ray craters [ http://www.sunlink.net/~torff/bwlunar10.html ] on the lunar surface tend to be much larger. NASA plans to launch MESSENGER [ http://sd-www.jhuapl.edu/ MESSENGER/ ] to the least explored [ http://www.soest.hawaii.edu/PSRdiscoveries/Jan97/ MercuryUnveiled.html ] terrestrial planet in 2004. |
|
Third Millennium, First Ecli
…
| Title |
Third Millennium, First Eclipse |
| Explanation |
The first eclipse of the third millennium [ http://sunearth.gsfc.nasa.gov/eclipse/extra/TLE2001Jan09.html ] is coming up! A total lunar eclipse mainly visible from [ http://sunearth.gsfc.nasa.gov/eclipse/extra/ TLE2001Jan09.html ] Europe, Asia, and Africa, will occur on January 9th as the full Moon [ http://antwrp.gsfc.nasa.gov/apod/ap000113.html ] glides through the long, but not so dark shadow of planet Earth [ http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=3&vbody=103&month=1&day=9¢ury=20&decade=0&year=1&hour=20&minute=20&rfov=30&fovmul=-1&bfov=30 ]. Why not so dark? Sunlight is actually scattered and refracted into Earth's shadow [ http://www.MrEclipse.com/Special/LEprimer.html ] by the atmosphere, a circumstance which can help create some striking photographs of the eclipsed Moon. For example, this image is a composite of photographs taken during the July 2000 total lunar eclipse. Early and late phases of the eclipse flank a deep exposure made [ http://www.mreclipse.com/LEphoto/LEphoto.html ] during totality. The feeble sunlight still shining on the lunar surface gives the Moon a dramatic dark red cast. While the July 2000 eclipse [ http://www.MrEclipse.com/LEphoto/TLE2000Jul16.html ] was not the first or last of any millennium, it was remarkable for being the longest eclipse for about the next 1,000 years, totality lasting an impressive one hour and 47 minutes. Totality for the January 9th eclipse will last just over one hour. |
|
Sail On, Stardust
| Title |
Sail On, Stardust |
| Explanation |
Spacecraft on long interplanetary voyages [ http://www-spof.gsfc.nasa.gov/stargaze/Sintro.htm ] often use the planets themselves as gravitational "sling shots" to boost them along their way. Launched [ http://stardust.jpl.nasa.gov/news/ commemorative.html ] in February of 1999 on a historic voyage to a comet, the Stardust spacecraft [ http://stardust.jpl.nasa.gov/news/ega/ ] is no different. On 15 January 2001 Stardust made its closest approach to planet Earth [ http://stardust.jpl.nasa.gov/news/status/010115.html ] since launch, coming within about 6,000 kilometers of the surface. It used this gravity assist maneuver [ http://www.jpl.nasa.gov/basics/bsf4-1.htm#gravity ] to increase its speed and alter its trajectory toward an encounter with comet Wild 2 [ http://www.ssep.org/stardust/wild-2.html ], which it should reach in 2004. Shortly before its time of closest approach, astronomer Gordon Garradd recorded this exposure [ http://www.ozemail.com.au/~loomberah/stardust.htm ] of Stardust sailing through the skies above Loomberah, Australia. Nearby and moving fast [ http://stardust.jpl.nasa.gov/news/ega/images.html ], the spacecraft appears as a streak against a background of faint stars in the constellation Cetus [ http://www.astronomical.org/constellations/cet.html ]. Stardust cruised within just 98,000 kilometers of the Moon [ http://stardust.jpl.nasa.gov/news/ega/lunar.html ] about 15 hours later. After collecting [ http://stardust.jpl.nasa.gov/tech/ aerogel.html ] dust from the tail of comet Wild 2, Stardust's voyage [ http://stardust.jpl.nasa.gov/mission/details.html ] will continue -- as it returns the samples to Earth in 2006. |
|
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. |
|
Asteroid and Galaxy
| Title |
Asteroid and Galaxy |
| Explanation |
Apollo class [ http://en.wikipedia.org/wiki/Apollo_asteroid ] asteroid 2006 VV2 [ http://neo.jpl.nasa.gov/cgi-bin/db?name=2006%20VV2 ] flashed past planet Earth [ http://antwrp.gsfc.nasa.gov/apod/ap041001.html ] in late March, approaching to within 3.4 million kilometers or about 8.8 times the Earth-Moon distance. Due to the proximity of its orbit to Earth and its estimated diameter of over 1 kilometer, 2006 VV2 is classified as [ http://www.cfa.harvard.edu/iau/lists/Dangerous.html ] a Potentially Hazardous Asteroid [ http://neo.jpl.nasa.gov/neo/pha.html ]. Telescopes large and small were trained on the much anticipated flyby [ http://www.rasc.ca/news/2006VV2.shtml ], the closest for a known asteroid of comparable size until the year 2036. This composite [ http://www.budgetastro.com/web/2006VV2-M81-Flyby.html ] telescopic view is from a series of images recorded over a period of about an hour on Mar. 28 from Vado, New Mexico. The asteroid begins near the center of the field and tracks down and to the left, apparently passing very near galaxy M81. Of course [ http://www.astr.ua.edu/gifimages/m81asteroid.html ], along with its companion [ http://antwrp.gsfc.nasa.gov/apod/ap060415.html ] galaxy M82 on the right, M81 is [ http://antwrp.gsfc.nasa.gov/apod/ap060707.html ] really 12 million light years away, compared to the asteroid's range [ http://www.cloudbait.com/science/2006vv2.html ] of a mere 15 light "seconds". |
|
Bright Venus
| Title |
Bright Venus |
| Explanation |
Have you seen a bright evening star [ http://antwrp.gsfc.nasa.gov/apod/ap990903.html ] in the western sky lately? That's no star, that's planet Venus the second "rock" from the Sun [ http://space.jpl.nasa.gov/ ]. Blazing at -4.6 magnitude [ http://liftoff.msfc.nasa.gov/academy/universe/ MAG.HTML ], Venus, after the Sun and Moon, is the third brightest celestial body in planet Earth's sky [ http://www.skypub.com/sights/sights.shtml ]. Venus is closer [ http://antwrp.gsfc.nasa.gov/apod/ap990612.html ] to the Sun than Earth and as Venus orbits [ http://astrosun.tn.cornell.edu/courses/astro201/ venus_phase.htm ] the Sun it is seen to go through phases [ http://euclid.sms.port.ac.uk/students/astrowise/ venus/demo1.html ] similar to the Moon. But unlike the Moon, as Venus waxes and wanes [ http://www.badastronomy.com/bitesize/ venus_phase.html ] its distance from Earth and hence its apparent size changes drastically. This causes Venus to look brighter [ http://www.science.nasa.gov/newhome/headlines/ ast14jun99_1.htm ] as it looms large in its crescent phases than when it is smaller and nearly full. Taken on January 28th, this dramatic picture finds a crescent Venus near its brightest to the right of a crescent Moon. The brilliant rivals seem poised above a satellite dish of the Scripps Satellite Oceanography Facility [ http://www.sio.ucsd.edu/about_scripps/scripps_tour/ siotour18.htm ]. Closer to the horizon, just below and to the right of the satellite dish, Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap000320.html ] pierces the twilight glow. |
|
Pluto in True Color
| Title |
Pluto in True Color |
| Explanation |
Pluto is mostly brown. The above picture captures the true colors of Pluto [ http://www.nineplanets.org/pluto.html ] as well as the highest surface resolution so far recovered [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2000DPS....32.4601Y ]. No spacecraft [ http://www.jpl.nasa.gov/ice_fire//pkexprss.htm ] has yet visited this most distant planet [ http://antwrp.gsfc.nasa.gov/apod/pluto.html ] in our Solar System [ http://www.nineplanets.org/overview.html ]. The above map [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999AJ....117.1063Y ] was created by tracking brightness changes from Earth [ http://antwrp.gsfc.nasa.gov/apod/earth.html ] of Pluto [ http://apod.gsfc.nasa.gov/cgi-bin/apod/apod_search?pluto+AND+charon ] during times when it was being partially eclipsed by its moon Charon [ http://www.nineplanets.org/pluto.html#charon ]. The map therefore shows the hemisphere of Pluto [ http://dosxx.colorado.edu/plutohome.html ] that faces Charon. Pluto [ http://www.solarviews.com/eng/pluto.htm ]'s brown color is thought dominated by frozen methane [ http://www.epa.gov/methane/ ] deposits metamorphosed by faint but energetic sunlight. The dark band below Pluto [ http://www.jpl.nasa.gov/ice_fire//alans.htm ]'s equator is seen to have rather complex coloring, however, indicating that some unknown mechanisms may have affected Pluto [ http://www.ucl.ac.uk/geolsci/edu/students/planet/student/work/pluto.htm ]'s surface. |
|
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. |
|
Verona Rupes: Tallest Known
…
| Title |
Verona Rupes: Tallest Known Cliff in the Solar System |
| Explanation |
Could you survive a jump off the tallest cliff in the Solar System? Quite possibly. Verona Rupes [ http://en.wikipedia.org/wiki/Verona_Rupes ] on Uranus [ http://www.nineplanets.org/uranus.html ]' moon Miranda [ http://www.nineplanets.org/miranda.html ] is estimated to be 20 kilometers deep -- ten times the depth of the Earth's Grand Canyon [ http://www.nps.gov/grca/ ]. Given Miranda [ http://en.wikipedia.org/wiki/Miranda_%28moon%29 ]'s low gravity, it would take about 12 minutes for a thrill-seeking adventurer [ http://video.google.com/videoplay?docid=2090669779765584576 ] to fall from the top, reaching the bottom at the speed of a racecar -- about 200 kilometers per hour. Even so, the fall might be survivable given proper airbag [ http://www.howstuffworks.com/airbag.htm ] protection. The above image [ http://photojournal.jpl.nasa.gov/catalog/PIA00044 ] of Verona Rupes was captured by the passing Voyager [ http://antwrp.gsfc.nasa.gov/apod/ap020831.html ] 2 robotic spacecraft in 1986. How the giant cliff was created remains unknown, but is possibly related to a large impact [ http://antwrp.gsfc.nasa.gov/apod/ap050308.html ] or tectonic [ http://en.wikipedia.org/wiki/Extensional_tectonics ] surface motion. |
|
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. |
|
Astronomer's Moon
| Title |
Astronomer's Moon |
| Explanation |
Jupiter is [ http://www.nineplanets.org/jupiter.html ] an astronomer's planet -- its large size and contrasting global cloud belts and zones [ http://antwrp.gsfc.nasa.gov/apod/ap030906.html ] allow detailed studies with a range of earthbound telescopes [ http://www.lpl.arizona.edu/alpo/ ]. On the other hand, most telescopic views of Jupiter's moons [ http://antwrp.gsfc.nasa.gov/apod/ap030227.html ] usually show only featureless, tantalizing points of light hovering near the ruling gas giant. But this impressive picture from a small, ground-based telescope reveals a stunning amount of detail [ http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/ Number/1752001/page/0/view/collapsed/sb/5/o/all/fpart/1 ] on Ganymede, a jovian moon about the same size as Earth's moon but at least 1,500 times farther away. The image was carefully constructed by combining and processing only the 409 sharpest frames from a total of 10,000 recorded at 30 frames per second by a digital camera. Ganymede's [ http://www.nineplanets.org/ganymede.html ] radius is about 2,600 kilometers indicating that the surface markings [ http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=503&vbody=399 &month=6&day=30&year=2007&hour=20&minute=05&rfov=2&fovmul=-1&bfov=30 &porbs=1&showsc=1 ] visible are as small as around 900 kilometers across. |
|
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/ ] |
|
Oceans Under Jupiter's Calli
…
| Title |
Oceans Under Jupiter's Callisto? |
| Explanation |
Why does Jupiter [ http://www.nineplanets.org/jupiter.html ]'s moon Callisto [ http://www.nineplanets.org/callisto.html ] alter the magnetic field [ http://www-istp.gsfc.nasa.gov/Education/Imagnet.html ] of Jupiter in its vicinity? Callisto itself does not have a strong magnetic field. One possible answer is that Callisto [ http://www.solarviews.com/eng/callisto.htm ] harbors sub-surface oceans of electrically conducting salt-water [ http://www.room103.com/archive/q_saltconductivity.htm ]. This hypothesis was bolstered recently [ http://www.nature.com/nsu/010726/010726-12.html ] by a new analysis of how Callisto creates and dissipates heat. Callisto [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA00362 ] is thought to create heat by the radioactive decay [ http://home.a-city.de/walter.fendt/phe/lawdecay.htm ] of internal rock -- a process that keeps the Earth's mantle [ http://earth.leeds.ac.uk/~greg/Conv.html ] molten. Callisto may not be able to dissipate this heat very efficiently, however, as it has thick layers of ice and rock on its surface. Perhaps this heat is enough to keep sub-surface water from freezing into ice. With this hypothesis [ http://space.com/scienceastronomy/solarsystem/callisto_water_010726.html ], Callisto joins two other of Jupiter's moons, Europa [ http://antwrp.gsfc.nasa.gov/apod/ap980310.html ] and Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap001218.html ], in candidates for sub-surface oceans. Callisto's oceans, however, might prove too hostile to support Earth-like life [ http://www.bbc.co.uk/education/darwin/loe/ ]. |
|
The 47 Ursae Majoris System
| Title |
The 47 Ursae Majoris System |
| Explanation |
Watching and waiting [ http://exoplanets.org/ ], astronomers have uncovered the presence of more than 70 planets orbiting stars other than the Sun. So far almost all these extrasolar planets [ http://cfa-www.harvard.edu/planets/ ] have crazy elongated orbits, lie uncomfortably close to their parent stars, or are found in bizarre, inhospitable systems. Yet a reported new planet [ http://www.nsf.gov/od/lpa/news/press/01/ pr0164.htm ] discovery indicates for the first time that a nearby sun-like star, 47 Ursae Majoris (47 UMa), has at least two planets in nearly circular orbits more reminiscent of Jupiter [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/ jupiterfact.html ] and Saturn [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/ saturnfact.html ] in our own familiar Solar System [ http://www.jpl.nasa.gov/basics/bsf1-1.html ]. The planets are too distant and faint to be photographed directly. Still, 13 years of [ http://exoplanets.org/esp/47uma/47uma.shtml ] spectroscopic observations of 47 UMa have revealed the wobbling [ http://exoplanets.org/doppler.html ] signature of a second planet intertwined with [ http://exoplanets.org/esp/47uma/47uma.shtml ] one previously known. In this artist's illustration [ http://extrasolar.spaceart.org/extrasol.html ], the worlds of 47 UMa [ http://antwrp.gsfc.nasa.gov/apod/ap971005.html ] hang over the rugged volcanic landscape of a hypothetical moon. The moon orbits the newly discovered planet [ http://exoplanets.org/esp/47uma/47uma_announce.html ], imagined here with Saturn-like rings, while the previously known planet is visible as a tiny crescent, close to the yellowish star. Closer still to 47 UMa is another tiny dot, a hypothetical [ http://www.fourmilab.to/terranova/ terranova.html ] Earth-like water world [ http://antwrp.gsfc.nasa.gov/apod/ap980530.html ]. About 51 light-years distant, 47 UMa can be found in planet Earth's sky near the Big Dipper [ http://www.astro.wisc.edu/~dolan/constellations/ constellations/Ursa_Major.html ]. |
|
Bright Planets, Crescent Moo
…
| Title |
Bright Planets, Crescent Moon |
| Explanation |
Early risers are currently enjoying the sight [ http://stardate.org/nightsky/planets/ ] of dazzling Venus [ http://www.nineplanets.org/venus.html ], near the eastern horizon as the morning star [ http://www.windows.ucar.edu/tour/link=/venus/ morning_star.html&edu=high ]. Recorded on October 7, this predawn skyview [ http://www.usno.navy.mil/pao/sky/sky_week.shtml ] does feature Venus at the upper right. It also includes a crescent Moon and Saturn (lower left). In fact, holding your fist at arms length would have easily covered [ http://chandra.harvard.edu/photo/scale.html ] both planets and the Moon in this 5 degree wide field. Earthshine [ http://antwrp.gsfc.nasa.gov/apod/ap020419.html ], sunlight reflected from planet Earth's dayside, illuminates features on the lunar nightside. A close inspection of Saturn itself reveals a nearby pinpoint of light corresponding to Saturn's [ http://saturn.jpl.nasa.gov/science/moons/index.cfm ] large moon Titan. Though the Moon has moved on, the tight triangle [ http://www.spaceweather.com/images2007/12oct07/ skymap_north.gif ] formed by Venus, Saturn, and Regulus (top), alpha star in the constellation Leo, will continue to look impressive in early morning skies over the next few days. Early bird astrophotographer Jay Ouellet also described Mars as [ http://www.spaceweather.com/images2007/11oct07/ skymap_north_mars.gif ] a "brilliant red diode" in his dark country sky east of Quebec City, Canada. Count the Stars: The Great World Wide Star Count [ http://www.windows.ucar.edu/citizen_science/starcount/ ] |
|
Mercury: A Cratered Inferno
| Title |
Mercury: A Cratered Inferno |
| Explanation |
Mercury's surface looks similar to our Moon's. Each is heavily cratered [ http://antwrp.gsfc.nasa.gov/apod/ap960906.html ] and made of rock. Mercury [ http://www.nineplanets.org/mercury.html ]'s diameter is about 4800 km, while the Moon [ http://antwrp.gsfc.nasa.gov/apod/moon.html ]'s is slightly less at about 3500 km (compared with about 12,700 km for the Earth [ http://antwrp.gsfc.nasa.gov/apod/earth.html ]). But Mercury [ http://www.oulu.fi/~spaceweb/textbook/mercury.html ] is unique in many ways. Mercury [ http://www.hawastsoc.org/solar/eng/mercury.htm ] is the closest planet to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap960518.html ], orbiting at about 1/3 the radius of the Earth's orbit [ http://aa.usno.navy.mil/faq/docs/seasons_orbit.html ]. As Mercury [ http://pds.jpl.nasa.gov/planets/welcome/mercury.htm ] slowly rotates, its surface temperature varies from an unbearably "cold" -180 degrees Celsius [ http://www.athena.ivv.nasa.gov/curric/weather/fahrcels.html ] to an unbearably hot 400 degrees Celsius [ http://www.astro.uu.se/history/Celsius_eng.html ]. The place nearest the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap980830.html ] in Mercury [ http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-mercury.html ]'s orbit changes slightly each orbit - a fact used by Albert Einstein [ http://antwrp.gsfc.nasa.gov/apod/ap000108.html ] to help verify the correctness of his then newly discovered theory of gravity: General Relativity [ http://www-groups.dcs.st-andrews.ac.uk/~history/HistTopics/General_relativity.html ]. The above picture [ http://nssdc.gsfc.nasa.gov/imgcat/html/object_page/m10_aom_18.html ] was taken by the only spacecraft ever to pass Mercury [ http://antwrp.gsfc.nasa.gov/apod/mercury.html ]: Mariner 10 [ http://www.hawastsoc.org/solar/eng/marin10.htm ] in 1974. |
|
Moon AND Sun
| Title |
Moon AND Sun |
| Explanation |
Today's composite image was made from 22 separate pictures of the Moon and Sun all taken from Chisamba, Zambia [ http://www.MrEclipse.com/TSE01reports/ TSE01Espenak.html ] during the total phase of the 2001 June 21 solar eclipse [ http://antwrp.gsfc.nasa.gov/apod/ap010622.html ]. The multiple exposures [ http://www.MrEclipse.com/TSE01reports/ TSE01reports.html#T01composite2 ] were digitally processed and combined to simultaneously show a wealth of detail which no single camera exposure or naked-eye observation could easily reveal. Most striking are the incredible flowing streamers of the Sun's outer atmosphere or solar corona [ http://csep10.phys.utk.edu/astr162/lect/sun/ corona.html ], notoriously difficult to see except when the new Moon blocks [ http://www.mreclipse.com/Special/SEprimer.html ] the bright solar disk. Features on the darkened near side of the Moon [ http://www.inconstantmoon.com/ ] can also be made out, illuminated by sunlight [ http://www.fourmilab.ch/earthview/vplanet.html ] reflected from a full Earth [ http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=3&vbody=103&month=6&day=21¢ury=20&decade=0&year=1&hour=12&minute=0&rfov=30&fovmul=-1&bfov=30 ]. A giant solar prominence seems to hang [ http://antwrp.gsfc.nasa.gov/apod/ap010726.html ] just beyond the Moon's eastern (left) edge while about one diameter farther east of the eclipsed Sun is the relatively [ http://sunearth.gsfc.nasa.gov/eclipse/TSE2001/TSE2001fig/ TSE2001fig15.GIF ] faint (4th magnitude) star 1 Geminorum [ http://www.astro.wisc.edu/~dolan/constellations/hr/ 2134.html ]. |
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