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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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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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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
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| 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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Ganymede: Moonquake World
| Title |
Ganymede: Moonquake World |
| Explanation |
Ganymede [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ganymede.html ] probably undergoes frequent ground shaking events not unlike terrestrial earthquakes. Ganymede [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/ganymede.html ], the largest moon of Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ] and the Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ], has a thick outer coating of water ice. Passing Voyager spacecraft found a large number of cracks and grooves in the ice so it is thought that Ganymede, like the Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950622.html ], has large shifting surface masses called tectonic plates. Ganymede 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, and is larger than the planets Mercury and Pluto. The NASA spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/ ] is scheduled to arrive at Jupiter is December of 1995. Tomorrow's picture: Europa: Ancient Water World |
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Callisto: Dark Smashed Iceba
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| 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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Jupiter, Io, and Ganymede's
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| Title |
Jupiter, Io, and Ganymede's Shadow |
| Explanation |
Jupiter [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/jupiter.html ], the solar system [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ]'s largest planet, is seen here next to Io [ http://antwrp.gsfc.nasa.gov/apod/ap950803.html ], its closest Galilean [ http://bang.lanl.gov/video/stv/arshtml/arstoc.html ] moon. On the cloud tops of Jupiter [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/jupiter.html ] near the left edge of the picture can be seen a dark circular spot which is caused by the shadow of Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ]'s largest moon Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ]. Jupiter [ http://nssdc.gsfc.nasa.gov/photo_gallery/PhotoGallery-Jupiter.html ]'s cloud tops show light bands and dark belts. The clouds are primarily composed of hydrogen [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#hydrogen ] and helium [ http://antwrp.gsfc.nasa.gov/apod/lib/glossary.html#helium ], but their intense colors are probably caused by very small amounts of heavier elements such as sulfur or organic (carbon-containing) compounds. |
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Saturn's Cleanest Moon: Ence
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| Title |
Saturn's Cleanest Moon: Enceladus |
| Explanation |
Enceladus [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/enceladus.html ] orbits Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap951018.html ] between the smaller Mimas [ http://antwrp.gsfc.nasa.gov/apod/ap950924.html ] and the larger Tethys [ http://antwrp.gsfc.nasa.gov/apod/ap951124.html ]. Enceladus is composed mostly of water ice and has the cleanest and purest ice surface in the Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ]. It's surface therefore appears nearly white. The surface also has many unusual groves and relatively few craters, like Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap951013.html ]'s moon Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ]. This indicates that the surface is young and/or newly reformed. To explain this, some astronomers speculate that Enceladus [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/enceladus.html ] is susceptible to some sort of volcanic [ http://antwrp.gsfc.nasa.gov/apod/ap950804.html ] activity. Enceladus was originally discovered in 1789 by William Herschel [ http://star.arm.ac.uk/history/herschel.html ]. |
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Uranus' Moon Miranda
| Title |
Uranus' Moon Miranda |
| Explanation |
NASA's robot spacecraft Voyager 2 passed the planet Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ] and its moons in 1986. While the cloud tops of Uranus [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/uranus.html ] proved to be rather featureless, the surface of Miranda [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/miranda.html ], the innermost of Uranus [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/uranus.html ]' large moons, showed several interesting features. Voyager 2 passed closer to Miranda [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/miranda.html ] than to any Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ] body and hence photographed it with the clearest resolution. Miranda's heavily cratered terrain shows grooves like Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap951208.html ]'s moon Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ] and several valleys and cliffs. Miranda is made of a roughly equal mix of ice and rock. Miranda was discovered by Gerard Kuiper in 1948. |
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Voyager's Preview of Galileo
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| Title |
Voyager's Preview of Galileo at Ganymede |
| Explanation |
NASA's robot spacecraft Galileo [ http://newproducts.jpl.nasa.gov/galileo/ ] began its long voyage to Jupiter in October of 1989. In December of last year it arrived in the Jovian system, beginning its unprecedented, detailed exploration by dropping a probe [ http://antwrp.gsfc.nasa.gov/apod/ap960123.html ] into the gas giant's atmosphere. By early this morning [ http://newproducts.jpl.nasa.gov/galileo/countdown/g1.html ] it will have accomplished another milestone [ http://nssdc.gsfc.nasa.gov/planetary/galileo_today.html ] in its ambitious mission. Now in orbit around Jupiter [ http://newproducts.jpl.nasa.gov/galileo/tourhilites.html ], Galileo will make its first close flyby of Ganymede, Jupiter's (and the solar system's) largest moon [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ] at 2:29 a.m. EDT. As planned [ http://antwrp.gsfc.nasa.gov/apod/lib/press1_gal.html ], approaching to within 524 miles, it will make a series of high resolution images of the surface which will reveal features as small as 33 feet across. This close-up color image from the Voyager 2 flyby in 1979 previews sights [ http://newproducts.jpl.nasa.gov/galileo/ganymede/vgrgan.html ] Galileo will see [ http://newproducts.jpl.nasa.gov/galileo/sepo/sepo.html ] in greater detail. Showing features as small as 3 miles across, it reveals a variety of terrain on Ganymede's icy surface, including impact craters with bright rays and long strips of light grooved structures suggesting large scale motions of the frozen crust. Galileo's flyby images will be stored onboard for playback and should be available during the week of July 10. |
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Erupting Volcanoes on Io
| Title |
Erupting Volcanoes on Io |
| Explanation |
Jupiter's moon Io has active volcanoes. The Voyager spacecraft [ http://www.jpl.nasa.gov/mip/voyager.html ] caught several erupting when they passed the energetic moon in 1979. In the above picture, several of Io's volcanoes [ http://antwrp.gsfc.nasa.gov/apod/ap950804.html ] are visible and one is seen actually erupting. Debris from this explosive event can be seen on the upper left of the photo, just beyond Io's edge. Io [ http://antwrp.gsfc.nasa.gov/apod/ap950803.html ]'s volcanism is thought to be caused by the large tidal distortions raised by Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ], Europa [ http://antwrp.gsfc.nasa.gov/apod/ap950905.html ], and Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ]. These tides stretch Io [ http://antwrp.gsfc.nasa.gov/apod/ap960719.html ], cause internal friction, and thus heat the interior. The hot interior then expands and forces its way out through volcanoes. Currently, the spacecraft Galileo [ http://antwrp.gsfc.nasa.gov/apod/ap951206.html ] is orbiting Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap951208.html ] and photographing Jupiter's Galilean moons [ http://antwrp.gsfc.nasa.gov/apod/ap960710.html ]. |
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Galileo's First Color Image
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| Title |
Galileo's First Color Image of Io |
| Explanation |
Above is the first color image [ http://newproducts.jpl.nasa.gov/galileo/ganymede/g1io.html ] of Jupiter's volcanic moon Io [ http://bang.lanl.gov/solarsys/io.htm ] released by the Galileo Project. (Io sounds like "eye-oh".) The image was made on June 25 when the Galileo spacecraft approached within 1.4 million miles. It reveals features as small as 14 miles across - comparable to the resolution of the best 1979 vintage Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager.html ] images. The Voyager flybys discovered active volcanos [ http://antwrp.gsfc.nasa.gov/apod/ap950804.html ] on Io's mottled surface [ http://antwrp.gsfc.nasa.gov/apod/ap950803.html ] and this image indicates that dramatic changes have occurred since [ http://newproducts.jpl.nasa.gov/galileo/status960718.html ], notably in the region of the Masubi volcano located in Io's southern hemisphere. This region, apparently covered with new deposits of sulfur and sulfur dioxide frost deposited by volcanic eruption, is seen as the pronounced white area at the bottom of the picture. While scientists continue to analyze this image and other recent Galileo data [ http://newproducts.jpl.nasa.gov/galileo/status960503.html ] the robot spacecraft will continue to explore Jupiter's moons [ http://NewProducts.jpl.nasa.gov/galileo/jup_sky/ ]. Its next scheduled close encounter [ http://newproducts.jpl.nasa.gov/galileo/tourhilites.html ] is set for September 6th with the moon Ganymede [ http://antwrp.gsfc.nasa.gov/apod/lib/gal_gan_lib.html ]. Higher resolution images of Io are also expected during the ongoing mission. |
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Galileo Views Io Eruption
| Title |
Galileo Views Io Eruption |
| Explanation |
Io's surface is active [ http://antwrp.gsfc.nasa.gov/apod/ap950803.html ]. Geyser-like eruptions from volcanoes on this Jovian [ http://antwrp.gsfc.nasa.gov/apod/lib/jupiter.html ] moon were seen by both Voyager spacecraft in 1979 and were also spotted this year in late June by Galileo's camera [ http://newproducts.jpl.nasa.gov/galileo/ganymede/p47209.html ] from a distance of about 600,000 miles. The blue plume seen at the moon's edge (magnified in the inset) arises from Ra Patera [ http://antwrp.gsfc.nasa.gov/apod/ap950804.html ], a large shield volcano, and extends about 60 miles above the surface. The blue color is attributed to condensing and freezing sulfur dioxide gas. Galileo images have also revealed that the plume glows in the dark - perhaps due to fluorescence of excited sulfur and oxygen ions. Io's surface is cold, its temperature averages about -230 degrees Fahrenheit [ http://www.unidata.ucar.edu/staff/blynds/tmp.html ], " so why is it so active? " The most likely cause is the gravitational tug of war over Io between Jupiter and the other Galilean moons which perturbs Io's orbit. The orbital changes would result in tidal force variations heating Io's interior and and generating the sulfurous volcanic activity [ http://volcano.und.nodak.edu/ ]. |
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Galileo Explores Europa
| Title |
Galileo Explores Europa |
| Explanation |
Details of the crazed cracks [ http://newproducts.jpl.nasa.gov/galileo/ganymede/p47183.html ] criss-crossing Europa's frozen surface [ http://antwrp.gsfc.nasa.gov/apod/ap960813.html ] are apparent in this mosaic of the Galileo spacecraft's latest images [ http://newproducts.jpl.nasa.gov/galileo/index.html ] of Jupiter's ice-covered moon. Curious white stripes, also seen by Voyager [ http://antwrp.gsfc.nasa.gov/apod/ap950905.html ], are clearly visible marking the center of the wide dark fractures. One theory suggests that "dirty geysers" erupting along the cracks deposited darker material followed by a flow of cleaner water ice which produced the stripe. The above image [ ftp://ftp.hq.nasa.gov/pub/pao/pressrel/1996/96-164.txt ] also shows an impact crater about 18.5 miles in diameter surrounded by white ejecta (lower left) and a curving x-pattern at bottom left which suggests fractures between icy plates filled with slush frozen in place. " Is there now or was there ever liquid water [ http://antwrp.gsfc.nasa.gov/apod/ap951118.html ] beneath Europa's surface [ http://antwrp.gsfc.nasa.gov/apod/ap960806.html ]? " These latest results still hold out that possibility -- and so the possibility of life. Europa, along with Mars [ http://antwrp.gsfc.nasa.gov/apod/ap960808.html ] and Saturn's moon Titan [ http://antwrp.gsfc.nasa.gov/apod/ap960716.html ] is considered to be one of the few places in our Solar System, beyond [ http://antwrp.gsfc.nasa.gov/apod/ap960701.html ] Earth, where primitive life forms could have developed. Galileo's close flyby of this tantalizing moon is scheduled for December [ http://newproducts.jpl.nasa.gov/galileo/background.html ] of this year. |
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Volcano Euboea Fluctus On Io
| Title |
Volcano Euboea Fluctus On Io |
| Explanation |
Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ]'s moon Io [ http://antwrp.gsfc.nasa.gov/apod/ap960815.html] is turning out to be our Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ]'s geologic powerhouse. The churning moon was photographed again just recently on June 27th and again shows signs of violent activity. Shown above are photographs [ http://antwrp.gsfc.nasa.gov/apod/ap960908.html http://galileo.ivv.nasa.gov/ganymede/082796.html ] of the volcano Euboea Fluctus taken at different times. The black and white photograph on the upper left was taken by the Voyager 1 [ http://antwrp.gsfc.nasa.gov/apod/ap960908.html http://vraptor.jpl.nasa.gov/voyager/voyager.html ] spacecraft when it flew by in 1979, the upper right and lower left photographs were taken in 1996 by the Galileo spacecraft [ http://antwrp.gsfc.nasa.gov/apod/ap951206.html ], while the lower right photograph is a color image taken by Voyager 2, also in 1979. The upper right Galileo picture has been artifically changed to simulate the color sensitivity of the Voyager [ http://antwrp.gsfc.nasa.gov/apod/ap960629.html ] 2 mission. The marked difference in the two images is highlighted by new red and yellow deposits. These markings may indicate that Euboea Fluctus erupts in an unusual fashion, possibly caused by an obstruction near the volcanic vent. |
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Eruption on Io
| Title |
Eruption on Io |
| Explanation |
There it goes again. Gas and rock were catapulted hundreds of kilometers into space as Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ]'s most volatile moon, Io [ http://www.seds.org/nineplanets/nineplanets/io.html ], showed yet another impressive volcanic display [ http://antwrp.gsfc.nasa.gov/apod/ap960805.html ] in this just-released photograph by the Hubble Space Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap970306.html ]. This time the culprit was Pele [ http://antwrp.gsfc.nasa.gov/apod/ap961205.html ], a volcano thought previously inactive since photographed by the passing Voyager [ http://www.jpl.nasa.gov/mip/voyager.html ] 1 spacecraft in 1979. The explosion is visible on Io [ http://galileo.ivv.nasa.gov/ganymede/g1io.html ]'s lower left in this false-color photograph [ http://oposite.stsci.edu/pubinfo/PR/97/21.html ], taken in July 1996. Io's thin atmosphere and low gravity allow volcanic plumes [ http://vulcan.wr.usgs.gov/Hazards/Tephra/haz_aircraft.html ] to rise higher than they would on Earth. |
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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
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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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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://bang.lanl.gov/solarsys/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/ap961214.html ]. This rock is so large its gravity [ http://loner.ccsr.uiuc.edu/cyberprof/physics/101/Lecture/L13P3.html ] makes it nearly spherical, and holds heavy gases near its surface. Today, this rock starts another orbit around its parent star [ http://antwrp.gsfc.nasa.gov/apod/ap960916.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/ap971026.html ]. |
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