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Jupiter's Moons Thebe, Amalt
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| Title |
Jupiter's Moons Thebe, Amalthea, and Metis |
| Explanation |
The robot spacecraft Galileo [ http://eis.jpl.nasa.gov/~skientz/galileo/ ] in orbit around Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ] has recently photographed the inner moons of Jupiter in greater detail than ever before. These pictures [ http://www2.jpl.nasa.gov/files/images/captions/pia02531.txt ] of Thebe [ http://www.solarviews.com/eng/thebe.htm ], Amalthea [ http://www.solarviews.com/eng/amalthea.htm ], and Metis [ http://www.solarviews.com/eng/metis.htm ] are shown to scale, and reveal details as small as three kilometers across. Amalthea [ http://www.seds.org/nineplanets/nineplanets/amalthea.html#amalthea ], by contrast, has a total length of about 200 kilometers. The moons [ http://antwrp.gsfc.nasa.gov/apod/ap971127.html ] are composed mostly of ice, are much smaller than Jupiter's more famous Galilean satellites [ http://www.jpl.nasa.gov/galileo/moons/moons.html ] (Io [ http://www.seds.org/nineplanets/nineplanets/io.html ], Europa [ http://www.seds.org/nineplanets/nineplanets/europa.html ], Ganymede [ http://www.seds.org/nineplanets/nineplanets/ganymede.html ], and Callisto [ http://www.seds.org/nineplanets/nineplanets/callisto.html ]), and orbit between Io and Jupiter's rings [ http://antwrp.gsfc.nasa.gov/apod/ap980916.html ]. Thebe appears dominated by a huge impact crater [ http://gdcinfo.agg.emr.ca/toc.html?/crater/world_craters.html ] 40 kilometers across. Astronomers are uncertain of the origin of the unusual white gash at the bottom of Amalthea [ http://www.jpl.nasa.gov/galileo/amalthea/ ]. |
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Io Rotating
| Title |
Io Rotating |
| Explanation |
The surface of Io is continually changing. Jupiter's moon [ http://antwrp.gsfc.nasa.gov/apod/ap990920.html ] is the home to many powerful volcanoes [ http://antwrp.gsfc.nasa.gov/apod/ap991126.html ] so active they are effectively turning the moon inside out. The above time-lapse sequence [ http://solarviews.com/cap/jup/vio1.htm ] is a composite of images taken during two space missions that approached the violent moon: Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager_fs.html ] and Galileo [ http://www.jpl.nasa.gov/galileo/mission.html ]. The sequence shows Io [ http://www.seds.org/nineplanets/nineplanets/io.html ] during a complete rotation, which corresponds to a complete revolution around Jupiter [ http://www.jpl.nasa.gov/galileo/Jovian.html ] since Io [ http://cass.jsc.nasa.gov/pub/research/outerp/io.html ] always keeps the same face toward the giant planet. The rampant volcanism is thought to be caused by Jupiter's more distant Galilean Moons [ http://solarviews.com/eng/galdisc.htm ] (Europa [ http://www.seds.org/nineplanets/nineplanets/europa.html ], Ganymede [ http://www.seds.org/nineplanets/nineplanets/ganymede.html ], and Callisto [ http://www.seds.org/nineplanets/nineplanets/callisto.html ]) pulling on Io and continually distorting its shape, causing internal frictional [ http://www.cord.edu/dept/physics/p128/lecture99_12.html ] heating. Io is composed mostly of rock, with the yellow color originating from sulfur [ http://chemlab.pc.maricopa.edu/periodic/S.html ]. The causes of many of the other colors remain a topic of research [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999Icar..140..265G ]. |
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Oceans Under Jupiter's Moon
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| 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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Jupiter, Europa, and Callist
…
| Title |
Jupiter, Europa, and Callisto |
| Explanation |
As the robot Cassini spacecraft [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ] rounds Jupiter [ http://www.jpl.nasa.gov/galileo/jupiter/jupiter.html ] on its way toward Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ], it has taken a sequence of images [ http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html ] of the gas giant with its four largest moons [ http://antwrp.gsfc.nasa.gov/apod/ap001118.html ]. Previously released images have highlighted Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap001212.html ] and Io [ http://antwrp.gsfc.nasa.gov/apod/ap001226.html ]. Pictured above [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02861 ] are the two remaining Galilean satellites [ http://www.jpl.nasa.gov/galileo/ganymede/discovery.html ]: Europa [ http://www.hawastsoc.org/solar/eng/europa.htm ] and Callisto [ http://cass.jsc.nasa.gov/pub/research/outerp/call.html ]. Europa [ http://www.jpl.nasa.gov/galileo/moons/europa.html ] is the bright moon superposed near Jupiter's Great Red Spot [ http://antwrp.gsfc.nasa.gov/apod/ap001123.html ], while Callisto is the dark moon near the frame edge. Callisto [ http://www.jpl.nasa.gov/galileo/moons/callisto.html ] is so dark that it would be hard to see here if its brightness was not digitally enhanced. Recent evidence indicates [ http://www.jpl.nasa.gov/galileo/news/release/press001216.html ] that both moons hold salt-water seas under surface ice that might be home to extra-terrestrial life. By noting the times that moons disappeared and reappeared behind Jupiter in 1676, Ole Roemer [ http://es.rice.edu/ES/humsoc/Galileo/Catalog/Files/roemer.html ] was able to make the first accurate estimation of the speed of light [ http://www.stats.uwaterloo.ca/~rwoldfor/papers/sci-method/paperrev/node4.html ]. |
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Europa Rotating
| Title |
Europa Rotating |
| Explanation |
Evidence has been mounting that beneath the vast planes of ice that cover Europa [ http://antwrp.gsfc.nasa.gov/apod/ap961120.html ] lies water -- liquid oceans that might be home to alien life [ http://www.sciam.com/0497issue/0497scicit7.html ]. The smallest of Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ]'s Galilean Moons [ http://solarviews.com/eng/galdisc.htm ] (which include Io [ http://www.seds.org/nineplanets/nineplanets/io.html ], Ganymede [ http://www.seds.org/nineplanets/nineplanets/ganymede.html ], and Callisto [ http://www.seds.org/nineplanets/nineplanets/callisto.html ]), Europa's deep interior is composed of mostly of silicate rock [ http://windows.arc.nasa.gov/cgi-bin/tour_def/glossary/silicate_rock.html ]. Upon close inspection, many surface cracks [ http://antwrp.gsfc.nasa.gov/apod/ap980310.html ] stop abruptly only to continue on somewhere else -- indicating surface plates that might be sliding [ http://antwrp.gsfc.nasa.gov/apod/ap970410.html ]. The above time-lapse sequence [ http://www.solarviews.com/cap/jup/veuropa1.htm ] is a composite of images taken during the Voyager spacecraft [ http://vraptor.jpl.nasa.gov/voyager/voyager_fs.html ] flyby of the moon twenty years ago. Not all regions are resolved in high detail. The movie shows Europa [ http://www.seds.org/nineplanets/nineplanets/europa.html ] during a complete rotation, which corresponds to a complete revolution around Jupiter [ http://www.jpl.nasa.gov/galileo/Jovian.html ] since Europa [ http://cass.jsc.nasa.gov/pub/research/outerp/euro.html ] always keeps the same face toward the giant planet. The cause of many of the surface colors on Europa [ http://www.solarviews.com/eng/europa.htm ] also remains a topic of research [ http://antwrp.gsfc.nasa.gov/apod/ap010116.html http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1988Icar...75..437B ]. |
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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/ ]. |
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Young Martian Terrain
| Title |
Young Martian Terrain |
| Explanation |
What caused the pits, ridges, and gullies on otherwise smooth Martian terrain? One hypothesis [ http://www.brown.edu/Administration/News_Bureau/2001-02/01-006.html ] is water. The lack of craters [ http://antwrp.gsfc.nasa.gov/apod/ap010108.html ] at this mid-latitude location indicates that the terrain is quite young by geological standards, perhaps only 100,000 years old. Were the terrain since saturated by water ice, that ice would soon evaporate into the thin Martian air [ http://www.pbs.org/saf/1109/features/mars.htm ]. Left over, however, might be fragile cake [ http://www.cakerecipe.com/ ]-like sand [ http://www.paccd.cc.ca.us/instadmn/physcidv/geol_dp/dndougla/SAND/Aboutsnd.htm ] that can be broken up by wind into pits and ridges. Consequences of this hypothesis [ http://news.bbc.co.uk/hi/english/sci/tech/newsid_1456000/1456708.stm ] include that even the Martian equator [ http://antwrp.gsfc.nasa.gov/apod/ap010628.html ] undergoes epochs of relative wet and dry, and that future spacefarers might be able to find water [ http://antwrp.gsfc.nasa.gov/apod/ap010417.html ] (ice) in a relatively mild climate near the Martian [ http://www.marsdaily.com/water.html ] equator. Pictured above [ http://ida.wr.usgs.gov/html/m03049/m0304950.html ] is young-ridged terrain that also shows evidence of a downhill flow [ http://antwrp.gsfc.nasa.gov/apod/ap000626.html ]. |
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Jagged Hills on Jupiter's Ca
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| Title |
Jagged Hills on Jupiter's Callisto |
| Explanation |
Why does Jupiter's moon Callisto have unusual jagged hills? This mystery came to light after the robot spacecraft [ http://galileo.jpl.nasa.gov/mission/space-intro.html ] Galileo [ http://galileo.jpl.nasa.gov/mission/mission.html ], in orbit around Jupiter [ http://www.nineplanets.org/jupiter.html ] since 1995, swooped past the dark moon [ http://antwrp.gsfc.nasa.gov/apod/ap980512.html ] in May. The resulting pictures [ http://www.jpl.nasa.gov/images/callisto/callisto_terrain_caption.html ] were the highest resolution yet obtained for a Jovian moon [ http://galileo.jpl.nasa.gov/moons/moons.html ]: objects as small as 3 meters across are discernable. The strange landscapes pictured above [ http://antwrp.gsfc.nasa.gov/apod/ap010828.html http://galileo.jpl.nasa.gov/news/release/press010822.html ] show areas rich in bright sharp mounds about 100 meters tall. A likely formation hypothesis [ http://galileo.jpl.nasa.gov/news/release/press010822.html ] holds that these hills are the result of ejecta thrown billions of years ago during a violent impact [ http://antwrp.gsfc.nasa.gov/apod/ap990711.html ]. The lower inset region apparently has undergone an epoch of relatively high ice-erosion [ http://members.edventures.com/terms/e/erosion/definition.html ], where dark rock has filled in some of the inter-hill regions. NASA [ http://www.nasa.gov/ ] has recently cleared Galileo [ http://galileo.jpl.nasa.gov/news/release/press010315.html ] to continue swooping Jupiter's moons [ http://www.sciam.com/2000/0200issue/0200johnson.html ] until 2003, when it will end its journey [ http://galileo.jpl.nasa.gov/news/release/press010315.html ] with a spectacular dive [ http://antwrp.gsfc.nasa.gov/apod/ap951208.html ] into Jupiter's atmosphere [ http://antwrp.gsfc.nasa.gov/apod/ap000429.html ]. |
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The Crater Chain
| Title |
The Crater Chain |
| Explanation |
NASA's robot spaceprobe Voyager 1 [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ], took this closeup image of the surface of Jupiter's crater scarred moon Callisto in 1979. A mysterious chain of craters is seen to extend diagonally across the image (upper left to lower right). What could cause the craters to line up in such a regular fashion? Scientists were at a loss to explain this crater chain along with several other chain like features observed on Callisto's surface. Fifteen years later, with the discovery of Comet Shoemaker-Levy 9 [ http://newproducts.jpl.nasa.gov/sl9/sl9.html ], also known as the "string of pearls" comet, [ http://antwrp.gsfc.nasa.gov/apod/ap950713.html ] the mystery was solved. Comets whose orbits stray too close to Jupiter are torn apart by the strong gravity. When the individual pieces, strung out along the orbital path of the comet hit an object like Callisto, the sequence of impacts produces a crater chain. For more information about the picture see the Split Comet Studies Page. [ http://cass.jsc.nasa.gov/split/split.html ] |
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Callisto Full Face
| Title |
Callisto Full Face |
| Explanation |
Callisto [ http://www.nineplanets.org/callisto.html ]'s surface shows its age. While probably formed at the same time as Io [ http://www.nineplanets.org/io.html ], the difference between the surfaces of these two moons of Jupiter [ http://www.solarviews.com/eng/jupiter.htm ] could hardly be greater. Io's surface [ http://antwrp.gsfc.nasa.gov/apod/ap970321.html ] is young, shows practically no impact craters, and is continually being repaved by the lava exploding [ http://antwrp.gsfc.nasa.gov/apod/ap000606.html ] from its many large volcanoes. Callisto [ http://www.jpl.nasa.gov/galileo/callisto/ ]'s surface is old, shows the highest density of impact craters [ http://www.lpi.usra.edu/pub/publications/slidesets/impacts.html ] in the Solar System [ http://www.exploratorium.edu/ronh/solar_system/ ], and harbors no volcanoes [ http://volcano.und.nodak.edu/vw.html ] or even any large mountains. Callisto's surface [ http://www.nature.com/nsu/010726/010726-12.html ] is one large ice-field, laced with cracks [ http://antwrp.gsfc.nasa.gov/apod/ap970218.html ] and craters [ http://antwrp.gsfc.nasa.gov/apod/ap010428.html ] from billions of years of collisions with interplanetary debris [ http://antwrp.gsfc.nasa.gov/apod/ap011205.html ]. The above image [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA03456 ] was taken in 2001 May and is, so far, the only complete global color image taken by the Jupiter-orbiting Galileo spacecraft [ http://galileo.jpl.nasa.gov/mission/space-intro.html ]. |
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Europa: Ancient Water World
| Title |
Europa: Ancient Water World |
| Explanation |
Beneath the cold icy surface of Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ]'s moon Europa [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/europa.html ] are probably the only oceans of water in our Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ] outside of Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950622.html ]. These oceans, possibly 50 kilometers deep, might also be the most likely local place to find extra-terrestrial life. Europa [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/europa.html ]'s smooth surface is unlike any other known planet or moon, giving evidence for relatively few craters or mountains. Europa was discovered by Galileo [ http://galileo.imss.firenze.it/museo/4/index.html ] and Marius [ http://seds.lpl.arizona.edu/billa/tnp/help.html#M ] in 1610. The NASA spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/ ] is scheduled to arrive at Jupiter in December of 1995. Tomorrow's picture: Callisto: Dark Smashed Iceball |
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Callisto: Dark Smashed Iceba
…
| Title |
Callisto: Dark Smashed Iceball |
| Explanation |
Callisto [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/callisto.html ] is a dirty battered world, showing the most beaten surface of Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ]'s major moons. Made of a rocky core covered by fractured ice, Callisto [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/callisto.html ]'s past collisions with large meteors are evident as large craters surrounded by concentric rings. The four largest moons of Jupiter: Io [ http://antwrp.gsfc.nasa.gov/apod/ap950803.html ], Europa [ http://antwrp.gsfc.nasa.gov/apod/ap950905.html ], Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ], and Callisto were all discovered by Galileo [ http://galileo.imss.firenze.it/museo/4/index.html ] and Marius [ http://seds.lpl.arizona.edu/billa/tnp/help.html#M ] in 1610 with early telescopes and are now known as the Galilean satellites. The NASA spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/ ] is scheduled to arrive at Jupiter is December of 1995. Tomorrow's picture: Distant Galaxies |
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Jupiter's Moon Amalthea
| Title |
Jupiter's Moon Amalthea |
| Explanation |
Amalthea is Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap951013.html ]'s fifth largest moon, much smaller than the four Galilean [ http://bang.lanl.gov/video/stv/arshtml/arstoc.html ] satellites Io [ http://antwrp.gsfc.nasa.gov/apod/ap950803.html ], Europa [ http://antwrp.gsfc.nasa.gov/apod/ap950905.html ], Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ], and Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap950906.html ]. The orbit of Amalthea [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/amalthea.html#amalthea ] is inside of these moons, and with its long axis always pointing toward Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ]. It's dark surface color is probably due to sulfur being expelled from Io [ http://antwrp.gsfc.nasa.gov/apod/ap950804.html ]. Amalthea is not massive enough for its internal gravity to make it spherical. Amalthea [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/amalthea.html ] was discovered in 1892 by Edward Barnard. |
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Galileo Photographs Ganymede
| Title |
Galileo Photographs Ganymede |
| Explanation |
Ganymede's surface is slowly being pulled apart. This photo of Ganymede [ http://antwrp.gsfc.nasa.gov/apod/lib/gany01_gal.txt ] was released earlier today [ http://newproducts.jpl.nasa.gov/galileo/ganymede/g1images.html ] by the Galileo team at NASA. The Galileo Spacecraft [ http://newproducts.jpl.nasa.gov/galileo/scpics.html ] arrived at Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ] in December 1995. In late June, the spacecraft passed within 10,000 kilometers of Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ]'s icy surface, and took pictures showing complex surface details for the first time. The line-like features in this photo are sunlit ridges rising above Ganymede [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ganymede.html ]'s ice-plains. The circular features are impact craters. Ganymede [ http://bang.lanl.gov/solarsys/ganymede.htm ] is the largest moon of Jupiter [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/jupiter.html ] and hence the largest of the four Galilean satellites: Io [ http://antwrp.gsfc.nasa.gov/apod/ap950803.html ], Europa [ http://antwrp.gsfc.nasa.gov/apod/ap950905.html ], Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap960627.html ], and Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap950906.html ]. |
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Ancient Cratered Plains on G
…
| Title |
Ancient Cratered Plains on Ganymede |
| Explanation |
The largest moon in the Solar System shows regions that are ancient and battered. The high density of craters demonstrate that patches of Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap960711.html ] are indeed billions of years old. This photo [ http://antwrp.gsfc.nasa.gov/apod/lib/pr47067.txt ] is one of a series [ http://antwrp.gsfc.nasa.gov/apod/lib/gal_gan_lib.html ] released by NASA [ http://newproducts.jpl.nasa.gov/galileo/ ] two days ago from the Galileo spacecraft orbiting Jupiter [ http://galileo.ivv.nasa.gov/fact/ ]. The large impact crater on the left is 19 kilometers across, while dark indentations in Ganymede [ http://newproducts.jpl.nasa.gov/galileo/ganymede/fact.html ]'s crusty surface-ice run diagonally. Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ] is composed of half rock and half water-ice. The Galileo spacecraft [ http://nauts.com/histpace/vehicles/histgalileo.html ] will continue to orbit Jupiter [ http://quest.arc.nasa.gov/galileo/About/jupiter.html ] over the next 16 months and send back data about Jupiter [ http://hea-www.harvard.edu/scied/Jupiter/jupiterpage.html ] and its four largest moons: Io [ http://antwrp.gsfc.nasa.gov/apod/ap950803.html ], Europa [ http://antwrp.gsfc.nasa.gov/apod/ap950905.html ], Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap960627.html ], and Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap950906.html ]. |
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When Moons and Shadows Dance
| Title |
When Moons and Shadows Dance |
| Explanation |
It's no wonder Jupiter is [ http://galileo.jpl.nasa.gov/jupiter/ jupiter.html ] a favorite target for [ http://www.lpl.arizona.edu/~rhill/alpo/jup.html ] even modest earthbound telescopes. The most massive planet in the solar system [ http://www.seds.org/nineplanets/ nineplanets/datamax.html ] with four of the largest moons also boasts the famous Great Red Spot [ http://csep10.phys.utk.edu/astr161/lect/jupiter/ redspot.html ], a giant hurricane-like storm system over three hundred years old. Recorded on December 15, 2002 between 7:19 and 8:40 UT, over a thousand digital images were processed and stacked to create this spectacular 21 frame animation of the Jovian system [ http://antwrp.gsfc.nasa.gov/apod/ap001118.html ]. South is up and as the Great Red Spot tracks across the face of Jupiter, innermost Galilean [ http://www.jpl.nasa.gov/galileo/ganymede/ discovery.html ] moon Io enters the scene at the far right. Io occults (passes in front of) the edge of the more sedately orbiting Ganymede with Io's shadow [ http://antwrp.gsfc.nasa.gov/apod/ap021207.html ] moving quickly across the gas giant's cloud tops, just below the Red Spot. While the moon Callisto is outside the field of view, its large, dark shadow is also visible crossing the Jovian disk at the upper left. Viewed from Earth, the orbits of the Galilean moons presently lie nearly edge-on, offering many chances to observe similar dances of Jupiter's moons [ http://skyandtelescope.com/observing/objects/planets/ article_771_1.asp ]. |
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Tomorrow's picture: Callisto
…
| Title |
Tomorrow's picture: Callisto Full Face [ http://antwrp.gsfc.nasa.gov/apod/ap961209.html ] |
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Tomorrow's picture: A Big Cl
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| Title |
Tomorrow's picture: A Big Cliff On Jupiter's Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap970218.html ] |
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Lightning on Jupiter
| Title |
Lightning on Jupiter |
| Explanation |
Does lightning occur only on Earth? Spacecraft in our Solar System have detected radio signals consistent with lightning [ http://wwwghcc.msfc.nasa.gov/lisotd.html ] on other planets, including Venus [ http://www.seds.org/nineplanets/nineplanets/venus.html ], Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ], Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ], Uranus [ http://www.seds.org/nineplanets/nineplanets/uranus.html ], and Neptune [ http://www.seds.org/nineplanets/nineplanets/neptune.html ]. In the above photograph [ http://galileo.ivv.nasa.gov/callisto/050197.html ], optical flashes from Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap970109.html ] were photographed recently by the Galileo orbiter [ http://galileo.ivv.nasa.gov/mission.html ]. Each of the circled dots indicates lightning [ http://www.nofc.forestry.ca/~kanderso/ltgfaq.html ]. The numbers label lines of latitude [ http://www.met.fsu.edu/explores/latlon.html ]. The size of the largest spot is about 500 kilometers across and might be high clouds illuminated by several bright lightning strokes. |
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Jupiter's Dry Spots
| Title |
Jupiter's Dry Spots |
| Explanation |
Known for its spectacular images of Jupiter's moons, Io [ http://antwrp.gsfc.nasa.gov/apod/ap970321.html ], Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap961223.html ], Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap970218.html ], and Europa [ http://antwrp.gsfc.nasa.gov/apod/ap970417.html ], the robot spacecraft Galileo has also aggressively explored the Jovian atmosphere. In December of 1995 [ http://antwrp.gsfc.nasa.gov/apod/ap951208.html ], Galileo's atmospheric probe descended into Jupiter's clouds [ http://antwrp.gsfc.nasa.gov/apod/ap961127.html ] and reported a surprising absence of water [ http://ccf.arc.nasa.gov/dx/basket/storiesetc/PROB1_22.html ]. It is now believed that the probe entered through one of Jupiter's dry spots [ http://galileo.ivv.nasa.gov/europa/p48700.html ], similar to the dark region in this image of the swirling Jovian cloud deck [ http://galileo.ivv.nasa.gov/europa/p48698.html ]. The smallest features visible here are tens of miles in size. These dry regions appear to correspond to locations where winds converge creating downdrafts. The downdrafts generate local cloudless clearings through which Jupiter's deeper warmer layers [ http://antwrp.gsfc.nasa.gov/apod/ap960123.html ] can be glimpsed. Just as the dark areas are extremely dry [ http://galileo.ivv.nasa.gov/status970605.html ], the surroundings are full of moisture. The contrast is analogous to the desert and tropics of Earth [ http://antwrp.gsfc.nasa.gov/apod/ap961012.html ]. |
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An Auroral Ring on Jupiter
| Title |
An Auroral Ring on Jupiter |
| Explanation |
Do other planets have aurora? Terrestrial [ http://work.ucsd.edu:5141/cgi-bin/http_webster?terrestrial ] and spacecraft observations have found evidence for aurora on Venus [ http://www.seds.org/nineplanets/nineplanets/venus.html ], Mars [ http://antwrp.gsfc.nasa.gov/apod/ap970609.html http://www.seds.org/nineplanets/nineplanets/mars.html ], Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ], Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ], Uranus [ http://www.seds.org/nineplanets/nineplanets/uranus.html ], and Neptune [ http://www.seds.org/nineplanets/nineplanets/neptune.html ]. In the above false-color photograph [ http://galileo.ivv.nasa.gov/callisto/043097.html ], a good portion of an auroral ring [ http://antwrp.gsfc.nasa.gov/apod/ap970609.html http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1996BAAS%2E%2E%2E28%2E2123P&db_key=AST&nosetcookie=1 ] was captured recently in optical light by the Galileo spacecraft [ http://galileo.ivv.nasa.gov/spacecraft.html ] in orbit around Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap970609.html http://antwrp.gsfc.nasa.gov/cgi-bin/cossc/apod_search?jupiter ]. Auroral rings [ http://antwrp.gsfc.nasa.gov/apod/ap970609.html http://www.geo.mtu.edu/weather/aurora/ ] encircle a planet's magnetic pole, and result from charged particles spiraling down magnetic field lines. Although the surroundings near Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap960803.html ] are much different than Earth [ http://antwrp.gsfc.nasa.gov/apod/ap961230.html ], the auroral rings [ http://antwrp.gsfc.nasa.gov/apod/ap970402.html ] appear similar. |
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New Horizons at Jupiter
| Title |
New Horizons at Jupiter |
| Explanation |
Headed for the first close-up exploration of the Pluto-Charon system [ http://www.plutoportal.net/ ] and the icy denizens of the Kuiper belt [ http://www.ifa.hawaii.edu/faculty/jewitt/kb.html ], NASA's New Horizons [ http://pluto.jhuapl.edu/mission.htm ] spacecraft is pictured here in an artist's vision of the robot probe outward bound. The dramatic scene [ http://www.swri.org/press/jest.htm ] depicts the 465 kilogram spacecraft about one year after a planned 2006 launch, following a flyby of gas giant Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap031114.html ]. While the Jupiter flyby [ http://www.swri.edu/9what/releases/ JEST.htm ] will be used as a gravity assist [ http://www.jpl.nasa.gov/basics/grav/primer.html ] maneuver to save fuel and cut travel time to the outer reaches of the Solar System [ http://www.seds.org/nineplanets/nineplanets/ nineplanets.html ], it will also provide an opportunity to test instruments and study the giant planet, its moons, and magnetic fields. The Sun is seen from eight hundred million kilometers away, with inner planets Earth, Venus, and Mercury aligned [ http://antwrp.gsfc.nasa.gov/apod/ap001014.html ] on the left. A dim crescent of outermost Galilean moon Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap010731.html ], orbiting Jupiter just inside of the spacecraft's trajectory, appears to the upper right of the fading Sun. Left of Jupiter itself is Europa [ http://antwrp.gsfc.nasa.gov/apod/ap030919.html ] and in the distant background are the faint, unresolved stars and dust clouds of the Milky Way [ http://home.arcor-online.de/axel.mellinger/ ]. New Horizons' planned arrival at Pluto-Charon [ http://pluto.jhuapl.edu/plutocharon.htm ] is in the summer of 2015. |
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Jupiter's Ring Halo
| Title |
Jupiter's Ring Halo |
| Explanation |
Why do small particles hover around Jupiter's rings? These particles form a previously unknown ring halo [ http://galileo.ivv.nasa.gov/callisto/PIA00658.html ], recently discovered by the robot spacecraft Galileo [ http://galileo.ivv.nasa.gov/spacecraft.html ] currently orbiting Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ]. Galileo obtained this image when on the far side of Jupiter - from this orientation scattered sunlight [ http://www.gla.ac.uk/Inter/CyberScience/cyber4.html#bluesky ] makes the halo ring [ http://galileo.ivv.nasa.gov/callisto/p48953.html ] visible. The amount of scattering indicates that halo particles are very small - perhaps 100 times smaller than the width of a human hair. Particles this small are believed to survive only for years, and so must somehow be replenished to Jupiter's ancient ring system [ http://antwrp.gsfc.nasa.gov/apod/ap970205.html ]. One possible explanation for this unusual halo is that electromagnetic fields [ http://www.ch.ic.ac.uk/local/physical/mi_5.html ] around Jupiter [ http://antwrp.gsfc.nasa.gov/apod/lib/jupiter.html ] gently push small charged particles out of the ring plane. This false color image [ http://galileo.ivv.nasa.gov/callisto/p48953.html ] has been artificially stretched in the vertical direction to highlight the ring halo. |
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Io: The Prometheus Plume
| Title |
Io: The Prometheus Plume |
| Explanation |
Two sulfurous eruptions are visible on Jupiter's volcanic moon Io [ http://antwrp.gsfc.nasa.gov/apod/ap970321.html ] in this color composite Galileo image [ http://galileo.ivv.nasa.gov/callisto/p48956.html ]. On the left, over Io's limb, a new bluish plume rises about 86 miles above the surface of a volcanic caldera [ http://www.op.dlr.de/ne-hf/SRL-1/p44422-caldera.html ] known as Pillan Patera. In the middle of the image, near the night/day shadow line, the ring shaped Prometheus plume is seen rising 45 miles above Io [ http://cass.jsc.nasa.gov/pub/research/outerp/io.html ] while casting a shadow to the right of the volcanic [ http://volcano.und.nodak.edu/vw.html ] vent. Named for the Greek god [ http://edweb.sdsu.edu/people/bdodge/scaffold/GG/titan.html ] who gave mortals fire, the Prometheus [ http://adhocalypse.arts.unimelb.edu.au/fcf/ucr/student/1996/ a.coulter/hot/prometh.htm ] plume is visible in every image ever made [ http://galileo.ivv.nasa.gov/ganymede/110696.html ] of the region dating back to the Voyager flybys [ http://nssdc.gsfc.nasa.gov/imgcat/html/ object_page/vg1_1636836.html ] of 1979 - presenting the possibility that this plume has been continuously active [ http://www-a.jpl.nasa.gov/galileo/ganymede/122096.html ] for at least 18 years. This image was recorded on June 28 at a distance of 372,000 miles. |
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Jupiter And Family
| Title |
Jupiter And Family |
| Explanation |
This composite image [ http://galileo.ivv.nasa.gov/ganymede/052997.html ] features classic portraits of members of one of the Solar System's [ http://antwrp.gsfc.nasa.gov/apod/ap961214.html ] most prominent families - Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap970920.html ] and its four large "Galilean" [ http://antwrp.gsfc.nasa.gov/apod/ap960830.html ] moons. Starting from the top the moons are Io [ http://antwrp.gsfc.nasa.gov/apod/ap970321.html ], Europa [ http://antwrp.gsfc.nasa.gov/apod/ap970117.html ], Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap961107.html ], and Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap961209.html ]. The top-to-bottom order is also the order of increasing distance from Jupiter. These are big moons indeed which attend the largest planet [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/jupiter.html ]. The smallest of the lot, Europa, is the size of Earth's moon [ http://antwrp.gsfc.nasa.gov/apod/ap970924.html ] while Ganymede is the largest moon in the Solar System. In fact, Ganymede with a diameter of 3,100 miles, is larger than the planets Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap961217.html ] and Pluto [ http://antwrp.gsfc.nasa.gov/apod/ap960311.html ]. The swirling Great Red Spot [ http://antwrp.gsfc.nasa.gov/apod/ap960827.html ] appears at the edge of Jupiter. A hurricane-like storm system that has persisted for over 300 years, two to three earths could fit inside it. Battered Callisto's [ http://antwrp.gsfc.nasa.gov/apod/ap950906.html ] image was recorded during the 1979 flyby of Voyager [ http://antwrp.gsfc.nasa.gov/apod/ap960629.html ]. The other portraits were taken by the Galileo spacecraft [ http://galileo.ivv.nasa.gov/spacecraft.html ] which began exploring the Jovian system in 1995. |
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Dark Volcano Active on Io
| Title |
Dark Volcano Active on Io |
| Explanation |
The surface of Io [ http://www.seds.org/nineplanets/nineplanets/io.html ] is changing even as we watch. The inset frame of Jupiter [ http://bang.lanl.gov/solarsys/jupiter.htm ]'s most active moon was taken by the robot spacecraft Galileo [ http://galileo.ivv.nasa.gov/spacecraft.html ] in April. Just last month the larger image [ http://galileo.ivv.nasa.gov/callisto/p49344.html ] was taken. The new large black spot reveals that a volcano named Pillan Patera [ http://antwrp.gsfc.nasa.gov/apod/ap970818.html ] has been erupting during the interim. A vast moonscape roughly the size of Arizona [ http://www.state.az.us/ ] has just been covered by some dark material. What is this material? [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1997Icar%2E%2E127%2E%2E221S&db_key=AST&nosetcookie=1 ] It's composition remains unknown although it is certainly different in color from the red material seen surrounding volcano Pele [ http://antwrp.gsfc.nasa.gov/apod/ap970623.html ] on the upper left. |
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Night Lightning on Jupiter
| Title |
Night Lightning on Jupiter |
| Explanation |
Why is there lightning on Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap970512.html ]? Lightning is a sudden rush of electrically charged particles [ http://www-spof.gsfc.nasa.gov/Education/Ielect.html ] from one location to another. To create lightning [ http://wwwghcc.msfc.nasa.gov/lisotd.html ], charges must first separate inside a cloud. On Earth [ http://antwrp.gsfc.nasa.gov/apod/ap971026.html ], drafts of colliding ice and water droplets usually create this charge separation, but what happens on Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ]? Many astronomers theorize that Jovian lightning [ http://galileo.ivv.nasa.gov/callisto/050197.html ] is also created in clouds containing water ice. To help investigate this, the above photograph [ http://galileo.ivv.nasa.gov/callisto/PIA01096.html ] was taken in October by the Galileo spacecraft [ http://galileo.ivv.nasa.gov/spacecraft.html ] now orbiting Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap971030.html ]. Clouds are dimly lit by sunlight reflected off Jupiter's moon Io [ http://bang.lanl.gov/solarsys/io.htm ]. The bright flashes appear to originate in active regions at the level where water clouds would exist, and illuminate an even lower cloud level containing ammonia [ http://www.nsc.org/ehc/ew/chems/ammonia.htm ]. One thing is for sure: lightning [ http://www.nofc.forestry.ca/~kanderso/ltgfaq.html ] on Jupiter is a lot brighter [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1992Icar%2E%2E%2E96%2E%2E%2E%2E1B&db_key=AST&nosetcookie=1 ] than lighting on Earth. |
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A Triple Eclipse on Jupiter
| Title |
A Triple Eclipse on Jupiter |
| Explanation |
Part of Jupiter is missing. Actually, three parts appear to be missing. In reality though, the three dark spots seen in the above photograph [ http://www.opi.arizona.edu/newsrel/science/jan98/3moons.htm ] are only shadows. The unusual alignment of three of Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ]'s moons between the Jovian giant [ http://bang.lanl.gov/solarsys/jupiter.htm ] and the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap960518.html ] was imaged last November 10th. The shadows of Io [ http://antwrp.gsfc.nasa.gov/apod/ap971110.html ], Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap950906.html ], and Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap961107.html ] move across Jupiter as these moons progress in their orbits. It was by noting the times of eclipse of Jupiter's moons in 1675 that Ole Roemer [ http://es.rice.edu/ES/humsoc/Galileo/Catalog/Files/roemer.html ] became the first person to measure [ http://www.pd.astro.it/~v_astro/ESO/astronomyonline/market/experiments/advanced/skills302.html ] the speed of light [ http://www.best.com/~dolphin/chistory.html ]. When a shadow from Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap980108.html ] crosses the Earth's surface, the people inside the shadow see an eclipse [ http://antwrp.gsfc.nasa.gov/apod/ap951024.html ] of the Sun. |
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Callisto Enhanced
| Title |
Callisto Enhanced |
| Explanation |
Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap980511.html ] is half rock and half ice. This moon of Jupiter [ http://www.hawastsoc.org/solar/eng/jupiter.htm ] is approximately the size of the planet Mercury [ http://www.seds.org/nineplanets/nineplanets/mercury.html ], making it the third largest moon in the Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap961214.html ], after Ganymede [ http://www.jpl.nasa.gov/galileo/ganymede/ ] and Titan [ http://www.seds.org/nineplanets/nineplanets/titan.html ]. Callisto [ http://www.seds.org/nineplanets/nineplanets/callisto.html ]'s icy surface is billions of years old, lacks any sign of volcanic activity [ http://antwrp.gsfc.nasa.gov/apod/ap970915.html ], and is densely covered with rifts and craters. These features are particularly apparent in this contrast-enhanced image [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01400 ] taken by the Galileo spacecraft [ http://www.jpl.nasa.gov/galileo/scpics.html ], and released last week. Visible near the image center is Valhalla [ http://www-a.jpl.nasa.gov/galileo/callisto/p48125.html ], one of the largest impact craters in the Solar System, measuring about 4,000 kilometers across. The rings and size of Valhalla [ http://www.hawastsoc.org/solar/eng/callisto.htm#valhalla ] make its appearance similar to the Caloris Impact Basin [ http://antwrp.gsfc.nasa.gov/apod/ap960120.html ] on Mercury. |
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Callisto in True Color
| Title |
Callisto in True Color |
| Explanation |
Callisto's surface has many stories to tell. The most distant of Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ]'s Galilean Moons [ http://www.jpl.nasa.gov/galileo/ganymede/discovery.html ], Callisto [ http://cass.jsc.nasa.gov/pub/research/outerp/call.html ] shows the highest density of impact craters [ http://antwrp.gsfc.nasa.gov/apod/ap971117.html ] in the Solar System, but harbors no volcanoes or even any large mountains. Callisto [ http://www.hawastsoc.org/solar/eng/callisto.htm ]'s surface is laced with cracks [ http://antwrp.gsfc.nasa.gov/apod/ap970218.html ] and craters [ http://bang.lanl.gov/solarsys/edu/craters.htm ] from billions of years of collisions with interplanetary debris. This image [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01298 ] shows |
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Pastel Planet, Triple Eclips
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| Title |
Pastel Planet, Triple Eclipse |
| Explanation |
This false-color [ http://hubblesite.org/newscenter/newsdesk/archive/releases/ 2004/30/ ] image of banded gas giant Jupiter shows a triple eclipse in progress on March 28 - a relatively rare [ http://antwrp.gsfc.nasa.gov/apod/ap980202.html ] event, even for a large planet with [ http://antwrp.gsfc.nasa.gov/apod/ap001118.html ] many moons. Captured by the Hubble Space Telescope's near-infrared camera are shadows of [ http://hubblesite.org/newscenter/newsdesk/archive/releases/ 2004/30/image/b ] Jupiter's moons Ganymede (left edge), Callisto (right edge) and Io, three black spots crossing the sunlit Jovian cloud tops. In fact, Io itself [ http://antwrp.gsfc.nasa.gov/apod/ap020706.html ] is visible as [ http://hubblesite.org/newscenter/newsdesk/archive/releases/ 2004/30/image/c ] a white spot near picture center with a bluish Ganymede above and to the right, but Callisto is off the right hand edge of the scene. Viewed from Jupiter's perspective, these shadow crossings [ http://antwrp.gsfc.nasa.gov/apod/ap030227.html ] would be seen as solar eclipses, analogous to the Moon's shadow [ http://antwrp.gsfc.nasa.gov/apod/ap040926.html ] crossing the sunlit face of planet Earth. Historically [ http://www.what-is-the-speed-of-light.com/ early-thoughts-speed-of-light.html ], timing the eclipses of Jupiter's moons allowed astronomer Ole Roemer [ http://www.college-optometrists.org/college/ museum/observatory/roemer.htm ] to make the first accurate measurement [ http://www.what-is-the-speed-of-light.com/ roemer-speed-of-light.html ] of the speed of light in 1676. |
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Jupiter and the Moon's Shado
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| Title |
Jupiter and the Moon's Shadowed Horizon |
| Explanation |
Early Tuesday [ http://science.nasa.gov/headlines/y2004/ 29nov_moonjupiter.htm ] morning, December 7th, June Croft thought the southeastern sky above Atmore, Alabama, USA was beautiful. Watching [ http://science.nasa.gov/headlines/y2004/ 06dec_geminids.htm ] the Moon rise through gossamer clouds, she noted, " ... the crescent Moon looked like it was held in the sky by a star just off its shadowed horizon." What was that star? Bright Jupiter of course, and some watched [ http://www.spaceweather.com/occultations/ gallery_07dec04.htm ] as the Moon actually occulted or passed in front of the Solar System's reigning gas giant [ http://antwrp.gsfc.nasa.gov/apod/ap031114.html ] planet. For astronomer Jimmy Westlake in Colorado, Jupiter was already hidden at moonrise that morning, but later he was able to record this lovely image, not unlike the view that inspired Croft. Seen through gossamer clouds, Jupiter along with large Jovian satellites [ http://antwrp.gsfc.nasa.gov/apod/ap041111.html ] Ganymede and Callisto (bottom to top) has emerged from behind the crescent Moon's shadowed horizon [ http://antwrp.gsfc.nasa.gov/apod/ap020419.html ]. |
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Cutaway Callisto: Ice, Rock,
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| Title |
Cutaway Callisto: Ice, Rock, and Ocean? |
| Explanation |
Cruising past the moons [ http://www.jpl.nasa.gov/galileo/Jovian.html ] of reigning gas giant Jupiter, Voyager [ http://vraptor.jpl.nasa.gov/voyager/vgrjup_fs.html ] and Galileo [ http://www.jpl.nasa.gov/galileo/index.html ] have returned tantalizing evidence for a liquid water ocean beneath the surface of Europa [ http://antwrp.gsfc.nasa.gov/apod/ap980910.html ]. Now researchers are reporting [ http://www.jpl.nasa.gov/galileo/news32.html ] telltale indications that the battered Jovian moon Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap980511.html ] may also harbor a subsurface ocean. This cutaway view [ http://photojournal.jpl.nasa.gov/ cgi-bin/PIAGenCatalogPage.pl?PIA01478 ] of Callisto shows a whitish 200 kilometer thick band of ice just beneath the moon's surface. The hypothetical ocean - indicated by the underlying light blue stripe - is potentially a salty layer of liquid water up to 10 kilometers thick, while the rest of the interior is seen as a jumble of rock and ice. Why a salty subsurface ocean? Magnetic measurements made [ http://www.jpl.nasa.gov/galileo/instruments/mag.html ] during Galileo flybys so far indicate Callisto's magnetic field is variable, analogous to results during Europa passes [ http://www.jpl.nasa.gov/galileo/europa/ ], and a plausible explanation is that Callisto [ http://www.jpl.nasa.gov/galileo/callisto/ ] too has a subsurface liquid layer. If the liquid were salt water it could easily carry electrical currents [ http://image.gsfc.nasa.gov/poetry//storm0/black3.html ] and produce the changing magnetic field [ http://image.gsfc.nasa.gov/poetry//maglab/maglab.html ]. |
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![Tomorrow's picture: Callisto Full Face [ http://antwrp.gsfc.nasa.gov/apod/ap961209.html ]](http://mm04.nasaimages.org/MediaManager/srvr?mediafile=/Size1/NVA2-4-NA/8135/degas_merc_mar10_big.jpg&userid=1&username=admin&resolution=1&servertype=JVA&cid=4&iid=NVA2&vcid=NA&usergroup=NASA_Astronomy_Picture_of_the_Day_Collecti-4-Admin&profileid=16)
![Tomorrow's picture: A Big Cliff On Jupiter's Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap970218.html ]](http://mm04.nasaimages.org/MediaManager/srvr?mediafile=/Size1/NVA2-4-NA/8182/solwind_soho.jpg&userid=1&username=admin&resolution=1&servertype=JVA&cid=4&iid=NVA2&vcid=NA&usergroup=NASA_Astronomy_Picture_of_the_Day_Collecti-4-Admin&profileid=16)
