|
|
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 ]. |
|
Southwest Mercury
| Title |
Southwest Mercury |
| Explanation |
The planet Mercury resembles a moon. Mercury [ http://www.seds.org/nineplanets/nineplanets/mercury.html ]'s old surface is heavily cratered [ http://liftoff.msfc.nasa.gov/Academy/SPACE/SolarSystem/Meteors/Craters.html ] like many moons. Mercury [ http://www.solarviews.com/eng/mercury.htm ] is larger than most moons but smaller than Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap990806.html ]'s moon Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap990304.html ] and Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap960717.html ]'s moon Titan [ http://antwrp.gsfc.nasa.gov/apod/ap990207.html ]. Mercury is much denser and more massive than any moon, though, because it is made mostly of iron. In fact, the Earth [ http://antwrp.gsfc.nasa.gov/apod/ap990131.html ] is the only planet more dense. A visitor to Mercury's surface [ http://antwrp.gsfc.nasa.gov/apod/ap960121.html ] would see some strange sights. Because Mercury [ http://www.oulu.fi/~spaceweb/textbook/mercury.html ] rotates exactly three times every two orbits around the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap951004.html ], and because Mercury [ http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-mercury.html ]'s orbit is so elliptical, a visitor to Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap990102.html ] might see the Sun [ http://antwrp.gsfc.nasa.gov/htmltest/gifcity/interv.html ] rise, stop in the sky, go back toward the rising horizon [ http://antwrp.gsfc.nasa.gov/apod/ap990619.html ], stop again, and then set quickly over the other horizon. From Earth [ http://antwrp.gsfc.nasa.gov/apod/ap980530.html ], Mercury's proximity to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap981212.html ] cause it to be visible only for a short time just after sunset or just before sunrise. |
|
Calderas And Cliffs Near Io'
…
| Title |
Calderas And Cliffs Near Io's South Pole |
| Explanation |
Braving intense radiation [ http://www-spof.gsfc.nasa.gov/Education/Iradbelt.html ] belts [ http://www-spof.gsfc.nasa.gov/Education/wotherms.html ], the Galileo spacecraft once again [ http://galileo.jpl.nasa.gov/news/status/ status000222.html ] flew past the surface of Jupiter's moon Io [ http://sse.jpl.nasa.gov/features/planets/ jupiter/io.html ] (sounds like EYE-oh [ http://spaceplace.jpl.nasa.gov/gll_io_fact.htm ]) on February 22. Combining high resolution black and white images from that flyby with color data recorded last summer has resulted in this dramatic view [ http://photojournal.jpl.nasa.gov/ cgi-bin/PIAGenCatalogPage.pl?PIA02534 ] of a region near the volcanic moon's south pole. An active and alien landscape, the bright white areas are likely due to sulfur dioxide frost and seem to be concentrated near ridges and cliffs. The three ominous black spots, each about 6-12 miles across, are volcanic craters or calderas [ http://volcano.und.nodak.edu/vwdocs/vwlessons/lessons/ Hot_Spot/Hot_Spot10.html ] covered with recent dark lava. A sinuous channel connects the lower left caldera with a yellowish lava flow. Io is small, but its continuous [ http://www-a.jpl.nasa.gov/galileo/ganymede/ 122096.html ] activity is driven by the drastic tides [ http://co-ops.nos.noaa.gov/restles1.html ] induced by Jupiter [ http://sse.jpl.nasa.gov/features/planets/ jupiter/jupiter.html ] and the other Jovian moons. It is estimated that the resulting volcanism [ http://volcano.und.edu/vwdocs/planet_volcano/Io/ Overview.html ] completely resurfaces Io [ http://antwrp.gsfc.nasa.gov/apod/ap970321.html ] every million years. |
|
Jupiter's Moons Thebe, Amalt
…
| 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/ ]. |
|
Ganymede: The Largest Moon i
…
| Title |
Ganymede: The Largest Moon in the Solar System |
| Explanation |
If Ganymede orbited the Sun, it would be considered a planet. The reason is that Jupiter [ http://galileo.jpl.nasa.gov/jupiter/jupiter.html ]'s moon Ganymede [ http://www.seds.org/nineplanets/nineplanets/ganymede.html ] is not only the largest moon in the Solar System [ http://www.seds.org/nineplanets/nineplanets/datamax.html ], it is larger than planets Mercury [ http://www.seds.org/nineplanets/nineplanets/mercury.html ] and Pluto [ http://dosxx.colorado.edu/plutohome.html ]. The robot spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/overview.html ] currently orbiting Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ] has been able to zoom by Ganymede [ http://www.solarviews.com/eng/ganymede.htm ] several times and snap many close-up pictures. Ganymede, shown above [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA00716 ] in its natural colors, sports a large oval dark region known as Galileo Regio [ http://www.jpl.nasa.gov/galileo/ganymede/121896.html ]. In general, the dark regions on Ganymede [ http://sse.jpl.nasa.gov/features/planets/jupiter/ganymede.html ] are heavily cratered, implying they are very old, while the light regions are younger and dominated by unusual grooves [ http://antwrp.gsfc.nasa.gov/apod/ap960711.html ]. The origin of the grooves is still under investigation [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1998Icar..135..317P ]. |
|
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 ]. |
|
Jupiter Eyes Ganymede
| Title |
Jupiter Eyes Ganymede |
| Explanation |
Who keeps an eye [ http://ciclops.lpl.arizona.edu/ciclops/ images_jupiter.html ] on the largest moon in the Solar System [ http://www.seds.org/nineplanets/nineplanets/overview.html ]? This moon, visible on the lower right, is Ganymede [ http://www.seds.org/nineplanets/nineplanets/ganymede.html ], and the planet it orbits, Jupiter [ http://antwrp.gsfc.nasa.gov/apod/jupiter.html ], seems to be keeping a watchful eye, as its Great Red Spot [ http://antwrp.gsfc.nasa.gov/apod/ap960802.html ] appears serendipitously nearby. This recently released [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02837 ] enhanced-contrast image from the robot spacecraft Cassini [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ] captures new details of the incredible intricacies of Jupiter's complex cloud [ http://antwrp.gsfc.nasa.gov/apod/ap000429.html ] patterns. Features as small as 250 kilometers can be seen. Counter-clockwise rotating high-pressure white ovals [ http://antwrp.gsfc.nasa.gov/apod/ap990105.html ] that are similar to the Great Red Spot [ http://antwrp.gsfc.nasa.gov/apod/ap001123.html ] appear in the red band below the spot. Between these spots are darker low-pressure systems [ http://www.usatoday.com/weather/wlowpres.htm ] that rotate clockwise. The hydrogen [ http://pearl1.lanl.gov/periodic/elements/1.html ] and helium [ http://pearl1.lanl.gov/periodic/elements/2.html ] that compose most of Jupiter's clouds is nearly invisible - the trace chemicals that give Jupiter these colors remain unknown [ http://antwrp.gsfc.nasa.gov/apod/ap960803.html ]. The Cassini spacecraft [ http://quest.arc.nasa.gov/saturn/qa/cassini/ ] is using Jupiter [ http://www.hawastsoc.org/solar/eng/jupiter.htm ] to pull it [ http://www.science.nasa.gov/newhome/headlines/ast24jun99_1.htm#gravityassist ] toward Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ], where it is scheduled [ http://www.jpl.nasa.gov/cassini/Mission/cruise.html ] to arrive in 2004. |
|
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. |
|
A Close-Up of Aurora on Jupi
…
| Title |
A Close-Up of Aurora on Jupiter |
| Explanation |
Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ] has aurorae [ http://www.geo.mtu.edu/weather/aurora/ ]. Like Earth [ http://antwrp.gsfc.nasa.gov/apod/ap990131.html ], the magnetic field [ http://liftoff.msfc.nasa.gov/academy/space/mag_field.html ] of the gas giant funnels charged particles released from the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap970411.html ] onto the poles. As these particles strike the atmosphere, electrons [ http://www-spof.gsfc.nasa.gov/Education/welect.html ] are temporarily knocked away from existing gas molecules [ http://www.chemistry.mcmaster.ca/faculty/bader/aim/ ]. Electric force [ http://www.colorado.edu/physics/2000/waves_particles/wavpart2.html ] attracts these electrons back. As the electrons [ http://www.aip.org/history/electron/ ] recombine to remake neutral molecules, auroral light [ http://antwrp.gsfc.nasa.gov/apod/ap980901.html ] is emitted. In the above recently released photograph [ http://oposite.stsci.edu/pubinfo/PR/2000/38/index.html ] by the Hubble Space Telescope [ http://www.stsci.edu/hst/ ] taken in ultraviolet light [ http://snoopy.gsfc.nasa.gov/~orfeus2/ultraviolet.html ], the aurorae [ http://antwrp.gsfc.nasa.gov/apod/ap000917.html ] appear as annular sheets around the pole. Unlike Earth's aurorae [ http://antwrp.gsfc.nasa.gov/apod/ap970402.html ], Jupiter's aurorae [ http://antwrp.gsfc.nasa.gov/apod/ap980123.html ] include several bright streaks and dots [ http://oposite.stsci.edu/pubinfo/PR/2000/38/faq.html ]. These marks are caused by magnetic flux tubes connecting Jupiter [ http://antwrp.gsfc.nasa.gov/apod/jupiter.html ] to its largest moons [ http://antwrp.gsfc.nasa.gov/apod/ap001118.html ]. Specifically, Io [ http://antwrp.gsfc.nasa.gov/apod/ap001024.html ] caused the bright streak on the far left, Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap000620.html ] caused the bright dot below center, and Europa [ http://www.seds.org/nineplanets/nineplanets/europa.html ] caused the dot to its right. |
|
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 ]. |
|
Jupiter, Io, and Shadow
| Title |
Jupiter, Io, and Shadow |
| Explanation |
Just as planets orbit our Sun, Jupiter's Moons [ http://antwrp.gsfc.nasa.gov/apod/ap001118.html ] orbit Jupiter. Pictured above [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02860 ] is the closest of Jupiter's Galilean Satellites [ http://www.jpl.nasa.gov/galileo/ganymede/discovery.html ], Io [ http://www.seds.org/nineplanets/nineplanets/io.html ], superposed in front of the giant planet it circles. To the left of Io [ http://www.hawastsoc.org/solar/eng/edu/moonio.htm ] is a dark spot that is its own shadow. The tremendous complexities that can be seen in Jupiter's banded, swirling atmosphere [ http://antwrp.gsfc.nasa.gov/apod/ap970310.html ] are being studied and may provide insight as to how Earth's atmosphere [ http://csep10.phys.utk.edu/astr161/lect/earth/atmosphere.html ] behaves. The above true-color contrast-enhanced image [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02860 ] was taken [ http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html ] two weeks ago by the robot spacecraft Cassini [ http://quest.arc.nasa.gov/saturn/qa/cassini/ ], currently passing Jupiter [ http://antwrp.gsfc.nasa.gov/apod/jupiter.html ] and on its way to Saturn [ http://antwrp.gsfc.nasa.gov/apod/saturn.html ] in 2004. Engineers continue to study [ http://www.jpl.nasa.gov/jupiterflyby/news/mission_status.html ] the Cassini spacecraft [ http://www.jpl.nasa.gov/basics/cassini.htm ] itself to understand why it required more force than normal to turn one of its maneuvering wheels. |
|
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 ]. |
|
Jupiter Moon Movie
| Title |
Jupiter Moon Movie |
| Explanation |
South is toward the top in this frame from a stunning movie featuring Jupiter and moons recorded last Thursday from the Central Coast of New South Wales, Australia. In fact, three jovian moons [ http://antwrp.gsfc.nasa.gov/apod/ap001118.html ] and two red spots are ultimately seen in the full video as they glide around [ http://skytonight.com/observing/objects/javascript/ 3307071.html ] the solar system's ruling gas giant. In the early frame above, Ganymede [ http://www.nineplanets.org/ganymede.html ], the largest moon in the solar system, is off the lower right limb of the planet, while intriguing Europa [ http://www2.jpl.nasa.gov/galileo/moons/europa.html ] is visible against Jupiter's cloud tops, also near the lower right. Jupiter's new red spot junior [ http://redspotjr.christone.net/ ] is just above the broad white band in the planet's southern (upper) hemisphere. In later frames, as planet and moons rotate (right to left), red spot junior moves behind Jupiter's left edge while the Great Red Spot [ http://heritage.stsci.edu/1999/29/index.html ] itself comes into view from the right. Also finally erupting into view at the right, is Jupiter's volcanic moon, Io [ http://www.nineplanets.org/io.html ]. To download the full 2 megabyte movie as an animated gif file, click on the picture. |
|
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. |
|
Io in True Color
| Title |
Io in True Color |
| Explanation |
The strangest moon in the Solar System [ http://www.nineplanets.org/overview.html ] is bright yellow. This picture [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02308 ], showing Io's true colors, was taken in 1999 July by the Galileo spacecraft [ http://www.jpl.nasa.gov/galileo/spacecraft.html ] currently orbiting Jupiter. Io's colors derive from sulfur [ http://chemlab.pc.maricopa.edu/periodic/S.html ] and molten silicate rock [ http://www.windows.ucar.edu/cgi- bin/tour_def/glossary/silicate_rock.html ]. The unusual surface of Io [ http://antwrp.gsfc.nasa.gov/apod/ap961029.html] is kept very young by its system of active volcanoes [ http://antwrp.gsfc.nasa.gov/apod/ap960805.html ]. The intense tidal gravity [ http://www.clupeid.demon.co.uk/tides/simple.html ] of Jupiter [ http://www.solarviews.com/eng/jupiter.htm ] stretches Io [ http://antwrp.gsfc.nasa.gov/apod/ap981016.html ] and damps wobbles caused by Jupiter's other Galilean moons [ http://www.jpl.nasa.gov/galileo/ganymede/discovery.html ]. The resulting friction [ http://www.pa.uky.edu/~phy211/Friction_book.html ] greatly heats Io [ http://antwrp.gsfc.nasa.gov/apod/ap980706.html ]'s interior, causing molten rock [ http://cmex.arc.nasa.gov/data/catalog/VolcanismOnMars/MoltenRock.html ] to explode through the surface. Io's volcanoes [ http://antwrp.gsfc.nasa.gov/apod/ap000606.html ] are so active that they are effectively turning the whole moon inside out. Some of Io [ http://www.nineplanets.org/io.html ]'s volcanic lava is so hot it glows in the dark [ http://adsabs.harvard.edu/cgi-bin/nph- bib_query?bibcode=1998Icar..135..181M ]. |
|
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/ ]. |
|
Ganymede: Torn Comet - Crate
…
| Title |
Ganymede: Torn Comet - Crater Chain |
| Explanation |
This striking line of 13 closely spaced craters [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA01610 ] on Jupiter's moon Ganymede [ http://cass.jsc.nasa.gov/pub/research/outerp/gany.html ] was photographed by the Galileo spacecraft in 1997. The picture covers an area about 120 miles wide and the chain of craters cuts across a sharp boundary between dark and light terrain. What caused this crater chain? Remarkably, the exploration of the Solar System [ http://sse.jpl.nasa.gov/index.html ], has shown that crater chains [ http://antwrp.gsfc.nasa.gov/apod/ap950715.html ] like this one are not unique [ http://neo.jpl.nasa.gov/images/moon.html ], though they were [ http://stardust.jpl.nasa.gov/news/news12.html ] considered mysterious until a dramatic object lesson was offered by comet Shoemaker-Levy 9. In 1994 many denizens of planet Earth [ http://antwrp.gsfc.nasa.gov/apod/ap971026.html ] watched as huge pieces of this torn comet [ http://antwrp.gsfc.nasa.gov/apod/ap990814.html ] slammed into Jupiter itself in a spectacular series of sequential impacts [ http://antwrp.gsfc.nasa.gov/apod/ap980804.html ]. It is very likely that similar torn comets from the early history of the Solar System are responsible for this and other crater chains [ http://astrosun.tn.cornell.edu/staff/bottke/crater_chain/ chain.html ]. |
|
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 |
|
Earth's Moon, A Familiar Fac
…
| Title |
Earth's Moon, A Familiar Face |
| Explanation |
The above mosaic of the Earth's Moon [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/luna.html ] was compiled from photos taken by the spacecraft Clementine [ http://nssdc.gsfc.nasa.gov/planetary/clementine.html ] in 1994. This image represents the side of the Moon familiar to Earth dwellers. The Moon [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/moon.html ] revolves around the Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950622.html ] about once every 28 days. Since its rate of rotation about its axis is also once in 28 days, it always keeps the same face toward the Earth. As the Moon travels around its orbit, the Earth based view of the half of the Moon [ http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-moon.html ] that faces the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ] changes causing the regular monthly progression of Lunar phases. Humans first crashed a spacecraft [ http://nssdc.gsfc.nasa.gov/cgi-bin/database/www-nmc?59-014A ] into the Moon in 1959, but the first humans to reach the Moon landed [ http://www.ksc.nasa.gov/history/apollo/apollo-11/apollo-11.html ] in 1969. There are now golf balls [ http://ees5-www.lanl.gov/APOLLO/a14.clsout2.html ] on the Moon. Tomorrow's picture: Ganymede: Moonquake World |
|
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 |
|
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. |
|
Jupiter, Io, and Ganymede's
…
| 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. |
|
Saturn's Cleanest Moon: Ence
…
| 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 ]. |
|
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. |
|
Jupiter, Moons and Bees
| Title |
Jupiter, Moons and Bees |
| Explanation |
Rising before the Sun on September 4, Jupiter and an old cresent Moon [ http://antwrp.gsfc.nasa.gov/apod/ap020419.html ] gathered in the dim constellation of Cancer [ http://www.coldwater.k12.mi.us/lms/planetarium/myth/ cancer.html ]. Watching from a hillside near Austin, Texas, planet Earth [ http://earthobservatory.nasa.gov/ ], astrophotographer Russell Croman recorded this view [ http://www.rc-astro.com/solar_system/moon/moonbees.html ] of their passing as clouds gracefully dimmed the brilliant moonlight. Earthshine illuminates [ http://www.amnh.org/exhibitions/codex/2A2r.html ] the lunar night side and on close inspection, bright Jupiter at the lower right appears tightly flanked [ http://antwrp.gsfc.nasa.gov/apod/ap980513.html ] by its own four large Galilean moons [ http://www.jpl.nasa.gov/galileo/ganymede/ discovery.html ]. Next to Jupiter lies a loose swarm of stars just below the clouds. The stars are the brighter members of the nearby star cluster M44, popularly known as the Beehive cluster [ http://antwrp.gsfc.nasa.gov/apod/ap980803.html ]. Croman's remarkable digital image has been processed only slightly to improve the visibility of the earthshine region and Jupiter's moons [ http://antwrp.gsfc.nasa.gov/apod/ap001118.html ]. |
|
Jupiter, Io and Shadow
| Title |
Jupiter, Io and Shadow |
| Explanation |
Pictured above [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA02860 ] is the innermost of Jupiter's Galilean satellites [ http://www.jpl.nasa.gov/galileo/ganymede/ discovery.html ], Io, superposed in front of the gas giant planet. To the left of Io [ http://www.seds.org/nineplanets/nineplanets/io.html ] is a dark spot that is Io's own shadow. A solar eclipse [ http://antwrp.gsfc.nasa.gov/apod/ap021206.html ] would be seen from within the shadow spot on Jupiter. Viewed from [ http://space.jpl.nasa.gov ] planet Earth, similar shadows of Jupiter's large moons can often be seen crossing [ http://antwrp.gsfc.nasa.gov/apod/ap980202.html ] the giant planet's disk. But during the next several months, the Galilean moons can also be seen crossing in front of each other [ http://skyandtelescope.com/observing/objects/planets/ article_771_1.asp ] as, for a while, their orbits lie nearly edge-on when viewed [ http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=105&vbody=3&month=12&day=20¢ury=20&decade=0&year=2&hour=21&minute=35&rfov=30&fovmul=-1&bfov=30 ] by earthbound observers. This true-color contrast-enhanced image was taken [ http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html ] two years ago by the robot spacecraft Cassini, as it passed Jupiter on its way [ http://antwrp.gsfc.nasa.gov/apod/ap021104.html ] to Saturn in 2004. |
|
Io Volcano Culann Patera
| Title |
Io Volcano Culann Patera |
| Explanation |
What causes the unusual colors surrounding Io's volcanoes? Io [ http://www.nineplanets.org/io.html], the innermost large moon [ http://www.jpl.nasa.gov/galileo/ganymede/discovery.html ] of Jupiter [ http://www.solarviews.com/eng/jupiter.htm ], is known to be the most tumultuous body [ http://antwrp.gsfc.nasa.gov/apod/ap010715.html ] in the Solar System [ http://www.nineplanets.org/overview.html ]. Approximately the size of Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap010218.html ], Io undergoes nearly continuous volcanic eruptions [ http://antwrp.gsfc.nasa.gov/apod/ap000606.html ] from an interior heated by gravitational tides [ http://burro.astr.cwru.edu/Academics/Astr221/Gravity/tides.html ] from Jupiter and Jupiter's other large moons. The robot spacecraft Galileo [ http://galileo.jpl.nasa.gov/mission/space-intro.html ] currently orbiting Jupiter has been monitoring the active volcano Culann Patera [ http://pirlwww.lpl.arizona.edu/missions/Galileo/releases/19May_i25culann.html ] over the past few years. The above images [ http://photojournal.jpl.nasa.gov/catalog/PIA03885 ] indicate that the volcano [ http://volcano.und.nodak.edu/volcanoes.html ] has produced not only red and black colored lava flows [ http://volcanoes.usgs.gov/Hazards/What/Lava/lavaflow.html ], but yellow sulfur [ http://pearl1.lanl.gov/periodic/elements/16.html ] patches from explosive plumes. Green colors may arise when these processes affect the same terrain. White patches may be caused, in part, by sulfur dioxide [ http://www.epa.gov/air/aqtrnd95/so2.html ] snow. As Galileo [ http://nssdc.gsfc.nasa.gov/planetary/galileo.html ] has fulfilled its mission objectives [ http://antwrp.gsfc.nasa.gov/apod/ap021218.html http://nssdc.gsfc.nasa.gov/planetary/galileo.html#objective ] and is running low on maneuvering fuel, NASA plans to crash [ http://astrobiology.arc.nasa.gov/news/expandnews.cfm?id=392 ] the spacecraft into Jupiter during 2003. |
|
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 ]. |
|
Ganymede: A Really Groovy Mo
…
| Title |
Ganymede: A Really Groovy Moon |
| Explanation |
Ganymede's surface is a wrinkled mess. As large ice-sheets shift on the moon's surface [ http://antwrp.gsfc.nasa.gov/apod/ap960710.html ], parts of the surface buckle causing high ridges, deep furrows, and parallel grooves. This photo [ http://antwrp.gsfc.nasa.gov/apod/lib/pr47065.txt ], taken by the Galileo spacecraft [ http://tid.cdscc.nasa.gov/Facts/galileo.html ] currently orbiting Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap951013.html ], was released yesterday [ http://newproducts.jpl.nasa.gov/galileo/ganymede/g1images.html ]. The large circular feature near the picture bottom is a large impact crater. The impact that caused this large crater also caused the strange dark ejecta seen to the crater's right. The Sun illuminates the scene from the lower left. The Galileo spacecraft [ http://www.jpl.nasa.gov/galileo/faq.html ] has also just discovered that Ganymede has a region of orbiting charged particles called a magnetosphere [ ftp://ftp.hq.nasa.gov/pub/pao/pressrel/1996/96-133.txt ] - a first for any moon. How Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ] is able to generate a magnetosphere [ http://www-spof.gsfc.nasa.gov/Education/Intro.html ] is a mystery. |
|
Voyager's Preview of Galileo
…
| 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. |
|
Galileo, Cassini, and the Gr
…
| Title |
Galileo, Cassini, and the Great Red Spot |
| Explanation |
Imagine a hurricane that lasted for 300 years! Jupiter's Great Red Spot indeed seems to be a giant hurricane-like storm system [ http://www.coaps.fsu.edu/~meyers/fig/vortex.html ] rotating with the Jovian clouds. Observed in 1655 by Italian-French astronomer Jean-Dominique Cassini [ http://www.jpl.nasa.gov/cassini/MoreInfo/casshuyg.html ] it is seen here over 300 years later - still going strong - in a mosaic of recent Galileo spacecraft images [ http://www.jpl.nasa.gov/galileo/ganymede/073196.html ]. The Great Red Spot is a cold, high pressure area 2-3 times wider than planet Earth. Its outer edge rotates in a counter clockwise direction [ http://bang.lanl.gov/solarsys/raw/jup/jupiter3.avi ] about once every six days. Jupiter's own [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/jupiter.html ] rapid rotation period [ http://www.kalmbach.com/astro/Bytes/JUPITER.html ] is a brief 10 hours. The Solar System's largest gas giant planet [ http://antwrp.gsfc.nasa.gov/apod/lib/jupiter.html ], it is presently well placed [ http://antwrp.gsfc.nasa.gov/apod/ap960723.html ] for evening viewing [ http://www.kalmbach.com/astro/Backyard/Jupiter.html ]. (APOD thanks to Alan Radecki for assembling a preliminary mosaic from the Galileo imagery!) |
|
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 ]. |
|
Galileo's First Color Image
…
| 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. |
|
Southwest Mercury
| Title |
Southwest Mercury |
| Explanation |
The planet Mercury resembles a moon. Mercury [ http://www.nineplanets.org/mercury.html ]'s old surface is heavily cratered [ http://liftoff.msfc.nasa.gov/Academy/SPACE/SolarSystem/Meteors/Craters.html ] like many moons. Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap030216.html 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/ap000620.html ] and Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap021104.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/ap010204.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/sun.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/ap010819.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/ap000320.html ], stop again, and then set quickly over the other horizon [ http://antwrp.gsfc.nasa.gov/apod/ap011209.html ]. From Earth, Mercury's proximity to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap981212.html ] causes it to be visible only for a short time just after sunset or just before sunrise. |
|
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 ]. |
|
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/ ]. |
|
Galileo Zooms in on Jupiter'
…
| Title |
Galileo Zooms in on Jupiter's Red Spot |
| Explanation |
What does the largest storm system ever recorded look like close-up? This storm system is Jupiter [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/jupiter.html ]'s Great Red Spot [ http://antwrp.gsfc.nasa.gov/apod/ap960802.html ] and it was captured recently [ http://newproducts.jpl.nasa.gov/galileo/ganymede/082296.html ] in detail by the robot spacecraft Galileo [ http://antwrp.gsfc.nasa.gov/apod/ap951206.html ] now in orbit around Jupiter [ http://antwrp.gsfc.nasa.gov/apod/lib/jupiter.html ]. Using real images from three color filters, the Galileo team was able to compute what a person would see if able to float just above this ancient rotating cloud system [ http://irtf.ifa.hawaii.edu/GalleryOfImages/grs5ch95a.html ]. But don't get too close - remember that Jupiter's Great Red Spot [ http://tnj.phys.tue.nl/Intro/redspot.html ] is a cold, high pressure area more than twice as wide as planet Earth [ http://antwrp.gsfc.nasa.gov/apod/ap960819.html ]. |
|
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. |
|
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 ]. |
|
Southwest Mercury
| Title |
Southwest Mercury |
| Explanation |
The planet Mercury resembles a moon. Mercury [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/mercury.html ]'s old surface is heavily cratered [ http://antwrp.gsfc.nasa.gov/apod/ap950924.html ] like many moons. Mercury [ http://bang.lanl.gov/solarsys/mercury.htm ] is larger than most moons but smaller than Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap951013.html ]'s moon Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ] and Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap960717.html ]'s moon Titan [ http://antwrp.gsfc.nasa.gov/apod/ap950923.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/ap960819.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/ap960912.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/ap951114.html ], stop again, and then set quickly over the other horizon. From Earth [ http://antwrp.gsfc.nasa.gov/apod/ap951118.html ], Mercury's proximity to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap960727.html ] cause it to be visible only for a short time [ http://www.maths.qmw.ac.uk/~lms/research/skyeye.html#planet ] just after sunset or just before sunrise. |
|
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. |
|
Tomorrow's picture: Fields o
…
| Title |
Tomorrow's picture: Fields of Minerals on Ganymede |
|
Tomorrow's picture: A Flyby
…
| Title |
Tomorrow's picture: A Flyby View of Ganymede |
|
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. |
|
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 ]. |
|
Impact On Europa
| Title |
Impact On Europa |
| Explanation |
This bull's-eye pattern marks the impact of a mountain-sized comet or asteroid [ http://antwrp.gsfc.nasa.gov/apod/ap960604.html ] on the icy surface of Jupiter's moon Europa [ http://antwrp.gsfc.nasa.gov/apod/ap961120.html ]. Recorded by the Galileo spacecraft [ http://galileo.ivv.nasa.gov/gem/ ] in April of this year, the composite false color image [ http://galileo.ivv.nasa.gov/ganymede/p48954.html ] clearly reveals the telltale concentric fractures [ http://antwrp.gsfc.nasa.gov/apod/ap960112.html ] which cover about 86 miles - roughly equivalent to the Island of Hawaii [ http://antwrp.gsfc.nasa.gov/apod/ap970302.html ]. The fat reddish and finer blue-green lines overlay the impact fractures and must therefore be younger surface features [ http://antwrp.gsfc.nasa.gov/apod/ap970410.html ] formed after the impact. The dark red color may be the result of a a relatively dirty water-ice mixture. The possibility of liquid water below the ice has fueled speculation that life may exist [ http://www.etext.org/Zines/Quanta/life.html ] on this large and distant moon [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/europa.html ]. |
|
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. |
|
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. |
|
Mysterious Features on Ganym
…
| Title |
Mysterious Features on Ganymede |
| Explanation |
Where is the rest of the circle? Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ]'s largest moon Ganymede [ http://bang.lanl.gov/solarsys/ganymede.htm ] has some truly unusual terrain, including the pictured half circle above [ http://galileo.ivv.nasa.gov/ganymede/PIA01087.html ] cut by nearly parallel curves. Full circles can be easily explained by impact craters [ http://antwrp.gsfc.nasa.gov/apod/ap971117.html ], but partial circles imply that some resurfacing [ http://galileo.ivv.nasa.gov/ganymede/PIA01089.html ] has occurred since the original impact. The diameter of the half circle is about 32 kilometers. Also of interest is a dense linear crater chain [ http://antwrp.gsfc.nasa.gov/apod/ap950715.html ] that cuts across the top of the half-circle. Mysteries like these are typically solved by the hard work of reconstructing a sequence of natural occurrences, which in this case may yield a better understanding of Ganymede [ http://galileo.ivv.nasa.gov/ganymede/ ]'s interesting past. |
|
Jupiter's Inner Moons
| Title |
Jupiter's Inner Moons |
| Explanation |
The potato-shaped inner moons of Jupiter [ http://www.seds.org/nineplanets/nineplanets/amalthea.html ] are lined-up in this mosaic [ http://galileo.ivv.nasa.gov/ganymede/PIA01076.html ]"family portrait" [ http://antwrp.gsfc.nasa.gov/apod/ap970929.html ] of these tiny Jovian satellites. The individual images were recorded over the last year by NASA's Galileo spacecraft and are scaled to the moons' relative sizes. Left to right in increasing order of distance from Jupiter [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/joviansatfact.html ] are Metis (longest dimension 37 miles), Adrastea (12 miles), Amalthea [ http://galileo.ivv.nasa.gov/amalthea/ ] (154 miles), and Thebe (72 miles). All these moons orbit in the zone between Io [ http://antwrp.gsfc.nasa.gov/apod/ap971110.html ] and Jupiter's rings [ http://antwrp.gsfc.nasa.gov/apod/ap970807.html ], are bombarded by high-energy ions within the Jovian magnetosphere [ http://antwrp.gsfc.nasa.gov/apod/ap961018.html ], and are probably locked in synchronous rotation [ http://www.seds.org/nineplanets/nineplanets/help.html#syncrot ] by Jupiter's strong gravity. Why are they shaped like potatoes? Like the asteroids [ http://antwrp.gsfc.nasa.gov/apod/ap970630.html ] and the diminutive moons of Mars [ http://antwrp.gsfc.nasa.gov/apod/ap961222.html ], their own gravity is not strong enough to mold them into spheres. |
|
|
