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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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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. |
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Oceans Under Jupiter's Moon
…
| Title |
Oceans Under Jupiter's Moon Ganymede? |
| Explanation |
The search for extraterrestrial [ http://www.seti.org/ ] life came back into our own Solar System [ http://www.seds.org/nineplanets/nineplanets/overview.html ] last week with the announcement [ http://www.jpl.nasa.gov/releases/2000/aguganymederoundup.html ] that there may be liquid oceans under the surface of Jupiter [ http://antwrp.gsfc.nasa.gov/apod/jupiter.html ]'s moon Ganymede [ http://www.jpl.nasa.gov/galileo/moons/ganymede.html ]. Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap000620.html ] now joins Callisto [ http://www.jpl.nasa.gov/galileo/news32.html ] and Europa [ http://www.jpl.nasa.gov/galileo/moons/europa.html ] as moons of Jupiter [ http://www.solarviews.com/eng/jupiter.htm ] that may harbor seas of liquid water under layers of surface ice [ http://antwrp.gsfc.nasa.gov/apod/ap980722.html ]. The ocean hypothesis surfaced as an explanation for Ganymede's unusually strong magnetic field [ http://www.igpp.ucla.edu/galileo/doc/n384/text.htm ]. Ganymede, the largest moon in the Solar System, also has the largest measured magnetic field [ http://www-spof.gsfc.nasa.gov/Education/Imagnet.html ] of any moon. Some exobiologists [ http://exobiology.nasa.gov/ssx/exobiology.html ] hypothesize that life may be able to emerge [ http://www.etext.org/Zines/Quanta/life.html ] in such an ocean, much as it did in the oceans of ancient Earth [ http://wwwcatsic.ucsc.edu/~eart1/Notes/Lec1.html ]. Above [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02583 ], a frame from a computer simulation [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenDownloadOpts.pl?PIA02583 ] shows what it would look like to fly over [ http://antwrp.gsfc.nasa.gov/apod/ap961025.html ] the surface of Ganymede, as extrapolated from photographs of the grooved moon [ http://antwrp.gsfc.nasa.gov/apod/ap960711.html ] taken by the robot spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/mission.html ] currently orbiting Jupiter. |
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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. |
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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. |
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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. |
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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: Torn Comet - Crate
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| 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 ]. |
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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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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 |
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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 ]. |
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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. |
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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. |
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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!) |
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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. |
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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. |
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When Moons and Shadows Dance
| Title |
When Moons and Shadows Dance |
| Explanation |
It's no wonder Jupiter is [ http://galileo.jpl.nasa.gov/jupiter/ jupiter.html ] a favorite target for [ http://www.lpl.arizona.edu/~rhill/alpo/jup.html ] even modest earthbound telescopes. The most massive planet in the solar system [ http://www.seds.org/nineplanets/ nineplanets/datamax.html ] with four of the largest moons also boasts the famous Great Red Spot [ http://csep10.phys.utk.edu/astr161/lect/jupiter/ redspot.html ], a giant hurricane-like storm system over three hundred years old. Recorded on December 15, 2002 between 7:19 and 8:40 UT, over a thousand digital images were processed and stacked to create this spectacular 21 frame animation of the Jovian system [ http://antwrp.gsfc.nasa.gov/apod/ap001118.html ]. South is up and as the Great Red Spot tracks across the face of Jupiter, innermost Galilean [ http://www.jpl.nasa.gov/galileo/ganymede/ discovery.html ] moon Io enters the scene at the far right. Io occults (passes in front of) the edge of the more sedately orbiting Ganymede with Io's shadow [ http://antwrp.gsfc.nasa.gov/apod/ap021207.html ] moving quickly across the gas giant's cloud tops, just below the Red Spot. While the moon Callisto is outside the field of view, its large, dark shadow is also visible crossing the Jovian disk at the upper left. Viewed from Earth, the orbits of the Galilean moons presently lie nearly edge-on, offering many chances to observe similar dances of Jupiter's moons [ http://skyandtelescope.com/observing/objects/planets/ article_771_1.asp ]. |
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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. |
|
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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Jupiter's Dry Spots
| Title |
Jupiter's Dry Spots |
| Explanation |
Known for its spectacular images of Jupiter's moons, Io [ http://antwrp.gsfc.nasa.gov/apod/ap970321.html ], Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap961223.html ], Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap970218.html ], and Europa [ http://antwrp.gsfc.nasa.gov/apod/ap970417.html ], the robot spacecraft Galileo has also aggressively explored the Jovian atmosphere. In December of 1995 [ http://antwrp.gsfc.nasa.gov/apod/ap951208.html ], Galileo's atmospheric probe descended into Jupiter's clouds [ http://antwrp.gsfc.nasa.gov/apod/ap961127.html ] and reported a surprising absence of water [ http://ccf.arc.nasa.gov/dx/basket/storiesetc/PROB1_22.html ]. It is now believed that the probe entered through one of Jupiter's dry spots [ http://galileo.ivv.nasa.gov/europa/p48700.html ], similar to the dark region in this image of the swirling Jovian cloud deck [ http://galileo.ivv.nasa.gov/europa/p48698.html ]. The smallest features visible here are tens of miles in size. These dry regions appear to correspond to locations where winds converge creating downdrafts. The downdrafts generate local cloudless clearings through which Jupiter's deeper warmer layers [ http://antwrp.gsfc.nasa.gov/apod/ap960123.html ] can be glimpsed. Just as the dark areas are extremely dry [ http://galileo.ivv.nasa.gov/status970605.html ], the surroundings are full of moisture. The contrast is analogous to the desert and tropics of Earth [ http://antwrp.gsfc.nasa.gov/apod/ap961012.html ]. |
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Jupiter And Family
| Title |
Jupiter And Family |
| Explanation |
This composite image [ http://galileo.ivv.nasa.gov/ganymede/052997.html ] features classic portraits of members of one of the Solar System's [ http://antwrp.gsfc.nasa.gov/apod/ap961214.html ] most prominent families - Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap970920.html ] and its four large "Galilean" [ http://antwrp.gsfc.nasa.gov/apod/ap960830.html ] moons. Starting from the top the moons are Io [ http://antwrp.gsfc.nasa.gov/apod/ap970321.html ], Europa [ http://antwrp.gsfc.nasa.gov/apod/ap970117.html ], Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap961107.html ], and Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap961209.html ]. The top-to-bottom order is also the order of increasing distance from Jupiter. These are big moons indeed which attend the largest planet [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/jupiter.html ]. The smallest of the lot, Europa, is the size of Earth's moon [ http://antwrp.gsfc.nasa.gov/apod/ap970924.html ] while Ganymede is the largest moon in the Solar System. In fact, Ganymede with a diameter of 3,100 miles, is larger than the planets Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap961217.html ] and Pluto [ http://antwrp.gsfc.nasa.gov/apod/ap960311.html ]. The swirling Great Red Spot [ http://antwrp.gsfc.nasa.gov/apod/ap960827.html ] appears at the edge of Jupiter. A hurricane-like storm system that has persisted for over 300 years, two to three earths could fit inside it. Battered Callisto's [ http://antwrp.gsfc.nasa.gov/apod/ap950906.html ] image was recorded during the 1979 flyby of Voyager [ http://antwrp.gsfc.nasa.gov/apod/ap960629.html ]. The other portraits were taken by the Galileo spacecraft [ http://galileo.ivv.nasa.gov/spacecraft.html ] which began exploring the Jovian system in 1995. |
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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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A Triple Eclipse on Jupiter
| Title |
A Triple Eclipse on Jupiter |
| Explanation |
Part of Jupiter is missing. Actually, three parts appear to be missing. In reality though, the three dark spots seen in the above photograph [ http://www.opi.arizona.edu/newsrel/science/jan98/3moons.htm ] are only shadows. The unusual alignment of three of Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ]'s moons between the Jovian giant [ http://bang.lanl.gov/solarsys/jupiter.htm ] and the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap960518.html ] was imaged last November 10th. The shadows of Io [ http://antwrp.gsfc.nasa.gov/apod/ap971110.html ], Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap950906.html ], and Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap961107.html ] move across Jupiter as these moons progress in their orbits. It was by noting the times of eclipse of Jupiter's moons in 1675 that Ole Roemer [ http://es.rice.edu/ES/humsoc/Galileo/Catalog/Files/roemer.html ] became the first person to measure [ http://www.pd.astro.it/~v_astro/ESO/astronomyonline/market/experiments/advanced/skills302.html ] the speed of light [ http://www.best.com/~dolphin/chistory.html ]. When a shadow from Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap980108.html ] crosses the Earth's surface, the people inside the shadow see an eclipse [ http://antwrp.gsfc.nasa.gov/apod/ap951024.html ] of the Sun. |
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Occultations and Rising Moon
…
| Title |
Occultations and Rising Moons |
| Explanation |
On April 23, the rising crescent Moon occulted [ http://www.skypub.com/occults/occults.html ] (passed in front of) Venus and Jupiter. The double occultation was a rare event [ http://antwrp.gsfc.nasa.gov/apod/ap980428.html ] and only visible from certain locations tracing a path [ http://www.skypub.com/occults/jupiter/980423a.html ] across Earth's surface. This dramatic telephoto picture [ http://eclipse.span.ch/moonsrising.htm ] was taken at [ http://eclipse.span.ch/live.htm ] one such location, Ascension Island [ http://volcano.und.nodak.edu/vwdocs/volc_images/africa/ascension.html ] in the South Atlantic. The sunlit crescent is over-exposed revealing the rest of the lunar surface illuminated by faint earthshine [ http://antwrp.gsfc.nasa.gov/apod/ap960530.html ]. Venus is emerging just beyond the crescent's tip and Jupiter is trailing above the dark lunar edge with a spot of light, Jupiter's moon Ganymede, between the lunar limb and the planet's disk. Look closely at Jupiter and you can see yet another Jovian moon [ http://antwrp.gsfc.nasa.gov/apod/ap970929.html ], Io, just visible against Jupiter's glare! |
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Ice Cusps on Europa
| Title |
Ice Cusps on Europa |
| Explanation |
Europa's icy crust has many unusual features. Pictured above [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01407 ] is part of Europa [ http://www.seds.org/nineplanets/nineplanets/europa.html ]'s southern hemisphere photographed by the Galileo spacecraft [ http://www.jpl.nasa.gov/galileo/spacecraft.html ] currently orbiting Jupiter [ http://pds.jpl.nasa.gov/planets/welcome/jupiter.htm ]. Europa is one of the largest moons of Jupiter [ http://www.jpl.nasa.gov/galileo/ganymede/discovery.html ], and is thought to have oceans of water [ http://antwrp.gsfc.nasa.gov/apod/ap970409.html ] underneath its ice-covered surface. Among many cracks and ridges [ http://antwrp.gsfc.nasa.gov/apod/ap980310.html ] appear dark cusp-shaped features running from the lower left toward the upper right. The origin of these features is not known for sure, but their shape is thought to indicate that large portions of Europa's crust [ http://antwrp.gsfc.nasa.gov/apod/ap961120.html ] move together, similar to tectonic motion [ http://pubs.usgs.gov/publications/text/dynamic.html ] of our Earth's crust [ http://www.windows.umich.edu/earth/interior/earths_crust.html ]. |
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Pastel Planet, Triple Eclips
…
| Title |
Pastel Planet, Triple Eclipse |
| Explanation |
This false-color [ http://hubblesite.org/newscenter/newsdesk/archive/releases/ 2004/30/ ] image of banded gas giant Jupiter shows a triple eclipse in progress on March 28 - a relatively rare [ http://antwrp.gsfc.nasa.gov/apod/ap980202.html ] event, even for a large planet with [ http://antwrp.gsfc.nasa.gov/apod/ap001118.html ] many moons. Captured by the Hubble Space Telescope's near-infrared camera are shadows of [ http://hubblesite.org/newscenter/newsdesk/archive/releases/ 2004/30/image/b ] Jupiter's moons Ganymede (left edge), Callisto (right edge) and Io, three black spots crossing the sunlit Jovian cloud tops. In fact, Io itself [ http://antwrp.gsfc.nasa.gov/apod/ap020706.html ] is visible as [ http://hubblesite.org/newscenter/newsdesk/archive/releases/ 2004/30/image/c ] a white spot near picture center with a bluish Ganymede above and to the right, but Callisto is off the right hand edge of the scene. Viewed from Jupiter's perspective, these shadow crossings [ http://antwrp.gsfc.nasa.gov/apod/ap030227.html ] would be seen as solar eclipses, analogous to the Moon's shadow [ http://antwrp.gsfc.nasa.gov/apod/ap040926.html ] crossing the sunlit face of planet Earth. Historically [ http://www.what-is-the-speed-of-light.com/ early-thoughts-speed-of-light.html ], timing the eclipses of Jupiter's moons allowed astronomer Ole Roemer [ http://www.college-optometrists.org/college/ museum/observatory/roemer.htm ] to make the first accurate measurement [ http://www.what-is-the-speed-of-light.com/ roemer-speed-of-light.html ] of the speed of light in 1676. |
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Ganymede: Torn Comet - Crate
…
| Title |
Ganymede: Torn Comet - Crater Chain |
| Explanation |
This remarkable 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? During the exploration of the Solar System [ http://ceps.nasm.edu:2020/ETP/ETP.html ], crater chains like this one have been discovered [ http://antwrp.gsfc.nasa.gov/apod/ap950715.html ] in several places [ http://antwrp.gsfc.nasa.gov/apod/ap971209.html ] and were 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/ap980801.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 [ http://www.skypub.com/comets/sw3.html ] from the early history of the Solar System are responsible for this and other crater chains [ http://www.jpl.nasa.gov/sl9/news80.html ]. |
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Io Aurora
| Title |
Io Aurora |
| Explanation |
Alluring aurora surrounding Io [ http://photojournal.jpl.nasa.gov/ cgi-bin/PIAGenCatalogPage.pl?PIA01637 ] (eye-oh) appear as a ghostly glow while the volcanic moon orbits [ http://antwrp.gsfc.nasa.gov/apod/ap970623.html ] within Jupiter's dark shadow. Gas giant Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ] is off to the right of this image, recorded in May by the robot Galileo spacecraft's solid state imaging camera [ http://www.jpl.nasa.gov/galileo/sepo/ ] from a distance of about 1.3 million kilometers. Energetic charged particles colliding with Io's atmospheric gases create the vivid colors and produce the red and green glow analogous to the aurora of Earth [ http://antwrp.gsfc.nasa.gov/apod/ap970402.html ]. The striking blue light is caused by dense volcanic plumes [ http://www-a.jpl.nasa.gov/galileo/ganymede/122096.html ] and may indicate regions electrically connected to Jupiter itself [ http://antwrp.gsfc.nasa.gov/apod/ap980123.html ]. |
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