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Iapetus Surface Composition
| Description |
Iapetus Surface Composition |
| Full Description |
The Cassini visual and infrared mapping spectrometer analyzed the surface composition of Saturn's moon Iapetus as Cassini flew over the polar region on Dec. 31, 2004. The image at left shows the reflectance at 4-microns, which is dominated by the minerals on Iapetus' surface. Two large craters are seen in this image. The polar water ice is relatively dark at this wavelength, so the ice cap is not seen. The next frame shows carbon dioxide on the surface. The carbon dioxide peaks at mid latitudes and shows less strength at the pole and along the equator (the dark band curving near the left edge of the image). The third frame shows the strength of water absorption on Iapetus. The brightest regions are due to water ice near the pole. The grayer areas indicate water bound to minerals on the surface. The color composite shows water as blue, carbon dioxide as green, and non-ice minerals as red. The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The visible and infrared mapping spectrometer team is based at the University of Arizona, Tucson. For more information about the Cassini-Huygens mission visit, http://saturn.jpl.nasa.gov. For more information about the visual and infrared mapping spectrometer visit http://wwwvims.lpl.arizona.edu/. *Credit*: NASA/JPL/GSFC |
| Date |
January 10, 2005 |
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The Secret Lives of Galaxies
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| Title |
The Secret Lives of Galaxies Unveiled in Deep Survey |
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The Secret Lives of Galaxies
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| Title |
The Secret Lives of Galaxies Unveiled in Deep Survey |
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Stereo Saturn
| Title |
Stereo Saturn |
| Explanation |
Get out your red/blue glasses [ http://img.arc.nasa.gov/archive/desert96/redblue.html ] and launch [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] yourself into this stereo [ http://cass.jsc.nasa.gov/research/stereo_atlas/SS3D.HTM ] picture of Saturn! The picture is actually composed from two images recorded weeks apart by the Voyager 2 spacecraft [ http://vraptor.jpl.nasa.gov/voyager/voyager_fs.html ] during its visit to [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ] the Saturnian System in August of 1981. Traveling at about 35,000 miles per hour, the spacecraft's changing viewpoint from one image to the next produced this exaggerated but pleasing stereo effect [ http://antwrp.gsfc.nasa.gov/apod/ap970404.html ]. Saturn is the second largest planet [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/saturn.html ] in the Solar System, after Jupiter. Its spectacular ring system [ http://ringmaster.arc.nasa.gov/saturn/saturn.html ] is so wide that it would span the space between the Earth and Moon. Although they look solid here, Saturn's [ http://antwrp.gsfc.nasa.gov/apod/ap000129.html ] rings consist of individually orbiting bits of ice and rock ranging in size from grains of sand to barn-sized boulders. |
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Zal Patera on Jupiter's Moon
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| Title |
Zal Patera on Jupiter's Moon Io |
| Explanation |
The Galileo orbiter [ http://www.jpl.nasa.gov/galileo/mission.html ]'s flyby of Io [ http://www.seds.org/nineplanets/nineplanets/io.html ] last November captured an unusual part of Jupiter [ http://antwrp.gsfc.nasa.gov/apod/jupiter.html ]'s volcanic moon. From 26,000 kilometers away, Zal Patera [ http://wwwflag.wr.usgs.gov/USGSFlag/Space/nomen/append5.html ] was found to be a cauldron of flowing lava [ http://antwrp.gsfc.nasa.gov/apod/ap991220.html ], gaseous vents [ http://antwrp.gsfc.nasa.gov/apod/ap970428.html ], and tremendous peaks [ http://antwrp.gsfc.nasa.gov/apod/ap960805.html ]. Red lava can be seen in the above picture [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02527 ] erupting along the base of the volcanic caldera, while cooling black lava lines the edge of a volcanic plateau. Shadow lengths indicate that the top of Zal Patera [ http://antwrp.gsfc.nasa.gov/apod/ap990513.html ] towers nearly 5 kilometers over Io [ http://galileo.jpl.nasa.gov/moons/io.html ]'s molten surface. Galileo zoomed past Io again last month [ http://galileo.jpl.nasa.gov/news/status/status000225.html ], and has begun beaming back images taken only 200 kilometers over Io's surface [ http://antwrp.gsfc.nasa.gov/apod/ap990920.html ]. |
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Venus, Moon, and Neighbors
| Title |
Venus, Moon, and Neighbors |
| Explanation |
Rising before the Sun on February 2nd, astrophotographer [ http://pages.prodigy.net/pam.orman/JoeGallery.html ] Joe Orman anticipated [ http://pages.prodigy.net/pam.orman/JoeAlmanac2000.html ] this apparition of the bright morning star [ http://ispec.scibernet.com/station/morn_star.html ] Venus near a lovely crescent Moon above a neighbor's house in suburban Phoenix, Arizona, USA. Fortunately, the alignment of bright planets and the Moon is one of the most inspiring sights in the night sky [ http://www.skypub.com/sights/skyevents/0004skyevents.html ] and one that is often easy to enjoy and share without any special equipment. Take tonight [ http://spacescience.com/headlines/y2000/ast30mar_1m.htm ], for example. Those blessed with clear skies can simply step outside near sunset and view a young crescent Moon very near three bright planets in the west Jupiter [ http://galileo.jpl.nasa.gov/ ], Mars [ http://mars.jpl.nasa.gov/mgs/ ], and Saturn [ http://www.jpl.nasa.gov/cassini/ ]. Jupiter will be the unmistakable brightest star near the Moon with a reddish Mars just to Jupiter's north and pale yellow Saturn directly above. Of course, these sky shows [ http://drumright.ossm.edu/astronomy/conjunctions.html ] create an evocative picture [ http://antwrp.gsfc.nasa.gov/apod/ap000310.html ] but the planets and Moon just appear to be near each other -- they are actually only approximately lined up and lie in widely separated orbits. Unfortunately, next month's highly publicized alignment of planets [ http://www.griffithobs.org/SkyAlignments.html ] on May 5th will be lost from view in the Sun's glare but such planetary alignments [ http://www.skypub.com/news/special/whypanic.html ] occur repeatedly and pose no danger [ http://www.badastronomy.com/bad/misc/planets.html ] to planet Earth. |
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Descent Panorama of Saturn's
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| Title |
Descent Panorama of Saturn's Titan |
| Explanation |
You're the first spacecraft ever to descend to Titan -- what do you see? Immediately after the Huygen's probe [ http://en.wikipedia.org/wiki/Huygens_probe ] pierced the cloud deck of Saturn [ http://en.wikipedia.org/wiki/Saturn_%28planet%29 ]'s moon Titan [ http://antwrp.gsfc.nasa.gov/cgi-bin/apod/apod_search?titan ] last January, it took a unique series of pictures of one of the Solar System [ http://www.windows.ucar.edu/our_solar_system/solar_system.html ]'s most mysterious moon's. Those pictures have recently been digitally stitched together to create spectacular panoramas and a dramatic descent movie [ http://photojournal.jpl.nasa.gov/catalog/PIA08117 ]. Pictured above [ http://photojournal.jpl.nasa.gov/catalog/PIA08114 ] is a panoramic fisheye view Huygen's obtained from about five kilometers above Titan's surface [ http://antwrp.gsfc.nasa.gov/apod/ap050117.html ]. The digital projection makes the local surface, mostly flat, appear as a ball, but allows one to see in all directions. Huygen's eventual landing site [ http://antwrp.gsfc.nasa.gov/apod/ap050518.html ] was in the large dark area below, just right of the center. This relatively featureless, dark, sandy basin appears to be surrounded by light colored hills to the right and a landscape fractured by streambeds and canyons [ http://antwrp.gsfc.nasa.gov/apod/ap050124.html ] above. Recent evidence [ http://uanews.org/cgi-bin/WebObjects/UANews.woa/16/wa/MainStoryDetails?ArticleID=12614 ] indicates that Titan's lakebeds and streambeds are usually dry but sometimes filled with a flashflood of liquid methane [ http://en.wikipedia.org/wiki/Methane ] from rare torrents of methane rain [ http://www.astrobio.net/news/article1413.html ]. |
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Europa: Ice Line
| Title |
Europa: Ice Line |
| Explanation |
This bright white swath cutting across the surface of icy Jovian moon Europa [ http://galileo.jpl.nasa.gov/moons/europa.html ] is known as Agenor Linea [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA00877 ]. In all about 1000 kilometers long and 5 kilometers wide, only a section is pictured here [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA01647 ] as part of a combined color and black and white image based on data from the Galileo spacecraft. Most linear features on Europa [ http://www.jpl.nasa.gov:80/galileo/europa/fact.html ] are dark in color but Agenor Linea is uniquely bright for unknown reasons. Also unknown is the origin of the reddish material along the sides. While these and other details of Europa's [ http://www.jpl.nasa.gov:80/galileo/news8.html ] surface formations remain mysterious, the general results of Galileo's exploration of Europa have supported the idea that an ocean of liquid water lies beneath [ http://photojournal.jpl.nasa.gov/ cgi-bin/PIAGenCatalogPage.pl?PIA01669 ] the cracked and frozen crust. An extraterrestrial liquid ocean [ http://science.nasa.gov/newhome/headlines/ast05mar98_1.htm ] holds out the tantalizing possibility [ http://quest.arc.nasa.gov/galileo/features/life.html ] of life. |
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Calderas And Cliffs Near Io'
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| 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. |
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The Surface of Titan
| Title |
The Surface of Titan |
| Explanation |
If sailing the hydrocarbon [ http://chemscape.santafe.cc.fl.us/chemscape/glossary/hdef.htm#24 ] seas of Titan [ http://antwrp.gsfc.nasa.gov/apod/ap990207.html ], beware of gasoline rain. Such might be a travel advisory [ http://travel.state.gov/travel_warnings.html ] issued one future day for adventurers visiting Titan [ http://antwrp.gsfc.nasa.gov/apod/ap000820.html http://www.seds.org/nineplanets/nineplanets/titan.html ], the largest moon of Saturn [ http://www.seds.org/nineplanets/nineplanets/saturn.html ]. New images of Titan [ http://antwrp.gsfc.nasa.gov/apod/ap951021.html ]'s surface were released [ http://despa.obspm.fr/planeto/titan_pueo.html ] last week from the Canada-France Hawaii Telescope [ http://www.cfht.hawaii.edu/ ] featuring the finest details [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1999DPS....31.4103C ] yet resolved. Peering into Titan [ http://ispec.scibernet.com/student-pages/saturn/titan.html ]'s thick smog [ http://www.aqmd.gov/smog/inhealth.html ] atmosphere with infrared [ http://www.us-gemini.noao.edu/public/infrared.html ] light, complex features interpreted as oceans, glaciers [ http://uanews.opi.arizona.edu/cgi-bin/WebObjects/ScienceResearch.woa/wo/XoEuK0m1padNGJ00ob/0.11.0.3?ArticleID=1926 ], and rock became visible. The high-resolution infrared image pictured above [ http://despa.obspm.fr/planeto/titan_pueo.html ] was made possible using an unblurring [ http://antwrp.gsfc.nasa.gov/apod/ap000725.html ] technique called adaptive optics [ http://www.lyot.obspm.fr/adaptive_optics.html ]. The interplanetary probe Cassini [ http://www.jpl.nasa.gov/cassini/ ] will reach Saturn and Titan in 2004 to better explore [ http://antwrp.gsfc.nasa.gov/apod/ap970829.html ] this unusual world. |
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Titania's Trenches
| Title |
Titania's Trenches |
| Explanation |
British astronomer Sir William Herschel [ http://star.arm.ac.uk/history/herschel.html ] discovered Titania and Oberon in January of 1787. He wasn't reading Shakespeare's [ http://the-tech.mit.edu/Shakespeare/works.html ]"A Midsummer Night's Dream" though, he was making the first telescopic observations of moons of the planet Uranus [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/uranus.html ] (a planet which he himself discovered in 1781 [ http://www-groups.dcs.st-and.ac.uk/~history/ HistTopics/Neptune_and_Pluto.html ]). In January of 1986, nearly 200 years later, NASA's robot explorer Voyager 2 became the only spacecraft to visit the remote Uranian [ http://antwrp.gsfc.nasa.gov/apod/ap990531.html ] system [ http://antwrp.gsfc.nasa.gov/apod/ap971103.html ]. Above is Voyager's highest resolution picture of Titania [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA00039 ], Uranus' largest moon. The picture is a composite of two images recorded from a distance of 229,000 miles. The icy, rocky world [ http://antwrp.gsfc.nasa.gov/apod/ap960304.html ] is seen to be covered with impact craters. A prominent system of fault valleys, some nearly 1,000 miles long, is visible as trench-like features near the terminator (shadow line). Deposits of highly reflective material which may represent frost can be seen along the sun-facing valley walls. The large impact crater near the top, known as Gertrude [ http://wwwflag.wr.usgs.gov/USGSFlag/Space/nomen/uranus/titacrat.html ], is about 180 miles across. At the bottom the 60 mile wide fault valley, Belmont Chasma [ http://wwwflag.wr.usgs.gov/USGSFlag/Space/nomen/uranus/titachas.html ], cuts into crater Ursula. Titania itself [ http://wwwflag.wr.usgs.gov/USGSFlag/Space/wall/titania.html ] is 1,000 miles in diameter. |
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Halo and Hexagons
| Title |
Halo and Hexagons |
| Explanation |
As a bright November Moon lit up the night sky last week, Gil Esquerdo spotted this lovely Moon halo overhead [ http://www.atoptics.co.uk/ ] at the Whipple Observatory on Mt. Hopkins, Arizona. In the foreground, the structure and individual component mirrors of Whipple's 10 meter gamma-ray telescope [ http://veritas.sao.arizona.edu/old/ VERITAS_whipple_photos.html ] actually block direct light from the lunar disk, emphasizing the halo in this dramatic view. The halo was caused by ice crystals in the thin high clouds above the observatory - crystals that are hexagonal in shape [ http://hyperphysics.phy-astr.gsu.edu/hbase/atmos/ moonhalo.html ] and produce the characteristic ring of light with a 22 degree radius. In fact, the ice crystal shapes are much like the flat, hexagonal mirrors of the specialized [ http://antwrp.gsfc.nasa.gov/apod/ap041015.html ] telescope in the picture. Used together the mirrors can collect brief flashes of optical light caused by high-energy gamma-rays impacting [ http://imagine.gsfc.nasa.gov/docs/science/how_l2/ cerenkov.html ] Earth's atmosphere. |
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Mountains of Titan
| Title |
Mountains of Titan |
| Explanation |
Peering through [ http://www.jpl.nasa.gov/news/news.cfm?release=2006-147 ] the thick, hazy atmosphere of Saturn's largest moon, an infrared camera onboard the Cassini [ http://saturn.jpl.nasa.gov/home/index.cfm ] spacecraft recorded this view of the tallest mountains ever seen on Titan [ http://antwrp.gsfc.nasa.gov/apod/ap060508.html ]. Captured during a flyby in late October, the high resolution, false-color mosaic [ http://photojournal.jpl.nasa.gov/catalog/PIA09032 ] shows a mountain range about 150 kilometers long and about 1.5 kilometers high - likened to the Sierra Nevada [ http://en.wikipedia.org/wiki/Sierra_Nevada_(US) ] mountain range of the western United States, planet Earth [ http://earthobservatory.nasa.gov/Newsroom/ NewImages/images.php3?img_id=11270 ]. Along Titan's mountain ridges lie bright deposits, thought to be methane [ http://www.astrobio.net/news/article1886.html ] snow or other organic material. The icy [ http://antwrp.gsfc.nasa.gov/apod/ap050610.html ] mountains of Titan were probably formed like Earth's mid-ocean ridges, from material welling up [ http://www.pbs.org/wgbh/aso/tryit/tectonics/ divergent.html ] to fill gaps created as surface tectonic plates [ http://www.ucmp.berkeley.edu/geology/tectonics.html ] spread apart. |
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Eclipse Moon Trail
| Title |
Eclipse Moon Trail |
| Explanation |
Tonight, Friday the 13th, October's big, bright, beautiful full Moon [ http://antwrp.gsfc.nasa.gov/apod/ap000113.html ] will be in the sky, rising as the sun sets. A time exposure of this evening's full Moon would show a brilliant circular arc or Moon trail tracing its celestial path. In fact, this single [ http://pages.prodigy.net/pam.orman/joemoon/ MoonPlanets_000120_2.html ], four hour long exposure from the evening of January 20 shows a full Moon trailing through hazy skies above [ http://pages.prodigy.net/pam.orman/ JoeGallery.html ] Phoenix, Arizona, USA. Of course, the picture also shows something you won't see tonight -- a total lunar eclipse [ http://www.mreclipse.com/Special/LEprimer.html ]. A lunar eclipse is caused when the full moon enters Earth's shadow [ http://image.gsfc.nasa.gov/poetry/ask/q2806.html ] and as the eclipsed Moon's light grows steadily fainter, the Moon trail becomes narrow and dim. The total eclipse phase, when the Moon passes completely within Earth's shadow [ http://space.jpl.nasa.gov/cgi-bin/wspace?tbody=3&vbody=103& month=1&day=21¢ury=20&decade=0&year=0&hour=04&minute=0& rfov=30&fovmul=-1&bfov=30 ], occurs near the middle of this Moon trail arc [ http://antwrp.gsfc.nasa.gov/apod/ap000905.html ]. But even during totality, the Moon trail is visible and noticeably red. Normally illuminated by sunlight which falls directly on its surface, during a total lunar eclipse the Moon is still illuminated [ http://antwrp.gsfc.nasa.gov/apod/ap991108.html ] by sunlight filtered and refracted through Earth's atmosphere. The refracted light lends the eclipsed Moon [ http://www.mreclipse.com/ ] a dim and reddish appearance. |
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Cassini Spacecraft Approache
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| Title |
Cassini Spacecraft Approaches Jupiter |
| Explanation |
A new spacecraft has entered the outer Solar System: Cassini [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ]. Launched in 1997 [ http://antwrp.gsfc.nasa.gov/apod/ap971016.html ] and bound for Saturn in 2004, Cassini sent back the above image [ http://ciclops.lpl.arizona.edu/ciclops/Images_jupiter.html ] last week while approaching the giant planet Jupiter [ http://www.seds.org/nineplanets/nineplanets/jupiter.html ]. Cassini [ http://quest.arc.nasa.gov/saturn/qa/cassini/ ] joins the Galileo spacecraft [ http://www.jpl.nasa.gov/galileo/mission.html] currently in orbit around Jupiter in studying the gas giant and its moons. In fact, observations [ http://www.jpl.nasa.gov/releases/2000/glextended.html ] involving both spacecraft [ http://www.jpl.nasa.gov/jupiterflyby/ ] simultaneously are planned in the coming months. This color picture [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA02972 ] was taken when Cassini was 81.3 million kilometers from Jupiter. The alternating dark and bright bands characteristic of Jupiter's cloud tops [ http://antwrp.gsfc.nasa.gov/apod/ap000429.html ] can be easily seen. Jupiter's moon Europa [ http://antwrp.gsfc.nasa.gov/apod/ap000825.html ] is also seen at the far right of the image casting a round shadow on the planet. |
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New Moons For Saturn
| Title |
New Moons For Saturn |
| Explanation |
Which planet has the most moons? For now, it's Saturn. Four newly discovered [ http://www.eso.org/outreach/press-rel/pr-2000/ phot-29-00.html ] satellites bring the ringed planet's total to twenty-two, just edging out Uranus' [ http://antwrp.gsfc.nasa.gov/apod/ap971103.html ] twenty-one for the most known [ http://www.eso.org/outreach/press-rel/pr-2000/ phot-19-00.html ] moons in the solar system. Of course, the newfound Saturnian satellites [ http://www.nasm.edu/ceps/etp/saturn/satmoons.html ] are not large [ http://antwrp.gsfc.nasa.gov/apod/ap000820.html ] and photogenic [ http://antwrp.gsfc.nasa.gov/apod/ap000129.html ]. The faint S/2000 S 1, the first discovered in the year 2000, is the tiny dot indicated at the lower right of this August 7th image made with the ESO 2.2 meter telescope at La Silla, Chile [ http://www.ls.eso.org/index.html ]. (An eye-catching spiral galaxy at the upper left is in the very distant background!) Unlike Saturn's larger moons whose almost circular orbits lie near the planet's equatorial plane, all four newly discovered moons have irregular [ http://www.obs-nice.fr/gladman/urhome.html ], skewed orbits drifting far from the planet. With sizes in the 10 to 50 kilometer range, they are are likely captured asteroids. The international team of astronomers involved in the discoveries hopes to get many observations of the tiny satellites [ http://www.obs-nice.fr/saturn/ ] allowing accurate orbital computations before Saturn is [ http://www.jpl.nasa.gov/cassini/ ] lost in the solar glare around March 2001. The team has also found several other irregular satellite candidates which are now being followed. Saturn's only previously known irregular satellite is Phoebe [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ phoebe.html ], discovered over 100 years ago by W. H. Pickering, |
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Double Asteroid 90 Antiope
| Title |
Double Asteroid 90 Antiope |
| Explanation |
This eight-frame animation is based on the first ever images [ http://www.boulder.swri.edu/~merline/press/ ] of a double asteroid [ http://www.boulder.swri.edu/~merline/press/release.txt ]! Formerly thought to be a single enormous chunk of rock, asteroid 90 Antiope [ http://cfa-www.harvard.edu/iau/lists/ NumberedMPs00001.html ] resides in the solar system's [ http://space.jpl.nasa.gov/ ] main asteroid belt [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ asteroids.html ] between Mars and Jupiter. Now, these premier images reveal Antiope to actually consist of two 50 mile wide asteroids separated by about 100 miles. Like weights on each end of an elastic string, the pair mutually orbit [ http://hyperphysics.phy-astr.gsu.edu/hbase/ orbv.html#bo ] their center of mass, or balance point in the space between them, once every 16.5 hours. Binary asteroids and asteroids with moons [ http://antwrp.gsfc.nasa.gov/apod/ap991014.html ] are believed to be rare, but observations of their orbits allow a direct determination of asteroid masses and densities. Surprisingly, Antiope and known [ http://www.cfht.hawaii.edu/News/PR_001026/ ] asteroid-moon [ http://antwrp.gsfc.nasa.gov/apod/ap990807.html ] systems are found to have densities closer to ice than rock, despite their relatively dark and unreflective surfaces. These sharp images were made at the Keck Observatory atop the Hawaiian volcano Mauna Kea using newly developed adaptive optics [ http://www.mtwilson.edu/Science/ AdapOpt/Overview/ ] technology to overcome the blurring effect [ http://antwrp.gsfc.nasa.gov/apod/ap000725.html ] of Earth's atmosphere. |
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Io: The Prometheus Plume
| Title |
Io: The Prometheus Plume |
| Explanation |
What's happening on Jupiter's moon Io? Two sulfurous eruptions are visible on Jupiter's volcanic moon Io [ http://antwrp.gsfc.nasa.gov/apod/ap040502.html ] in this color composite image [ http://photojournal.jpl.nasa.gov/catalog/PIA00703 ] from the robotic Galileo spacecraft [ http://en.wikipedia.org/wiki/Galileo_spacecraft ] that orbited Jupiter from 1995 to 2003. At the image top, over Io [ http://en.wikipedia.org/wiki/Io_%28moon%29 ]'s limb, a bluish plume rises about 140 kilometers above the surface of a volcanic caldera [ http://www.op.dlr.de/ne-hf/SRL-1/p44422-caldera.html ] known as Pillan Patera [ http://pirlwww.lpl.arizona.edu/~turtle/Releases/7Oct_pillan.html ]. In the image middle, near the night/day shadow line, the ring shaped Prometheus plume is seen rising about 75 kilometers above Io [ http://antwrp.gsfc.nasa.gov/apod/ap030120.html ] while casting a shadow below the volcanic [ http://antwrp.gsfc.nasa.gov/apod/ap051002.html ] vent. Named for the Greek god [ http://www.pantheon.org/articles/p/prometheus.html ] who gave mortals fire [ http://en.wikipedia.org/wiki/Fire ], the Prometheus [ http://en.wikipedia.org/wiki/Prometheus ] plume is visible in every image ever made 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 [ http://antwrp.gsfc.nasa.gov/apod/ap970428.html ] continuously active for at least 18 years. The above digitally sharpened [ http://en.wikipedia.org/wiki/Unsharp_mask ] image was originally recorded in 1997 on June 28 from a distance of about 600,000 kilometers. |
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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. |
|
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 ]. |
|
Io: Moon Over Jupiter
| Title |
Io: Moon Over Jupiter |
| Explanation |
How big is the Jovian moon Io [ http://www.seds.org/nineplanets/ nineplanets/io.html ]? The most volcanic body [ http://volcano.und.nodak.edu/vwdocs/planet_volcano/ other_worlds.html ] in the Solar System, Io (usually pronounced "EYE-oh") is 3,600 kilometers in diameter, about the size of planet Earth's single large natural satellite [ http://antwrp.gsfc.nasa.gov/apod/ap010127.html ]. Gliding past Jupiter [ http://www.jpl.nasa.gov/jupiterflyby/ ] at the turn of the millennium, the Cassini spacecraft captured this awe inspiring view [ http://ciclops.lpl.arizona.edu/ciclops/images_jupiter.html ] of active Io [ http://www.jpl.nasa.gov/galileo/moons/io.html ] with the largest [ http://www.seds.org/nineplanets/nineplanets/ datamax.html ] gas giant as a backdrop, offering a stunning demonstration of the ruling planet's relative size [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/ jupiterfact.html ]. Although in the picture Io [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA02879 ] appears to be located just in front of the swirling Jovian clouds, Io hurtles around its orbit once every 42 hours at a distance of 420,000 kilometers or so from the center of Jupiter [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/ joviansatfact.html ]. That puts it nearly 350,000 kilometers above Jupiter's cloud tops [ http://antwrp.gsfc.nasa.gov/apod/ap010215.html ], roughly equivalent to the distance between Earth and Moon [ http://antwrp.gsfc.nasa.gov/apod/ap980904.html ]. The Cassini spacecraft [ http://www.jpl.nasa.gov/cassini/english/spacecraft/ ] itself was about 10 million kilometers from Jupiter when recording the image data. |
|
Red, White, and Blue Sky
| Title |
Red, White, and Blue Sky |
| Explanation |
Contrasting colors in this beautiful sunset sky [ http://www.schursastrophotography.com/10dastro/ vensat070107.html ] were captured on June 30 from Clear Creek Canyon Observatory in central Arizona, USA. The twilight scene includes brilliant [ http://www.digitalsky.org.uk/venus/ shadow-of-venus.html ] Venus as the evening star [ http://www.johnpratt.com/items/astronomy/eve_morn.html ], with a bright Saturn just above it, shining through thin clouds. The two wandering [ http://antwrp.gsfc.nasa.gov/apod/ap070407.html ] planets [ http://antwrp.gsfc.nasa.gov/apod/ap010601.html ] were a mere 1 degree apart or so, about twice the width of the full Moon rising above the eastern horizon on the other side of the sky. In fact, such serene skyviews [ http://www.spaceweather.com/ ] were possible from all over planet Earth as Venus and Saturn approached a conjunction [ http://en.wikipedia.org/wiki/Astronomical_conjunction# Conjunctions_of_planets_in_right_ascension_2005-2020 ]. Regulus, alpha star of the constellation Leo [ http://en.wikipedia.org/wiki/Leo_(constellation) ], is above and to the left of the close planetary pairing. At dusk, lights in tonight's sky will also feature Venus and Saturn low in the west and separated by about 2 degrees. |
|
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. |
|
Welcome to the Moon Hotel
| Title |
Welcome to the Moon Hotel |
| Explanation |
The most detailed proposal [ http://www.rombaut.nl/ ] so far for a hotel and resort [ http://antwrp.gsfc.nasa.gov/apod/ap001209.html ] destination on the Moon [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ luna.html ] (!) has been prepared by Dutch [ http://www.xs4all.nl/~carlkop/maanhotel/lunatic.html ] architect Hans-Jurgen Rombaut. The harsh lunar environment [ http://www.frc.ri.cmu.edu/projects/lri/Luna/report/ des_approach.html#REF61557 ] posed serious design challenges [ http://members.aol.com/dsfportree/ explore.htm ] but the Moon's low, one-sixth-Earth gravity [ http://www.windows.ucar.edu/cgi-bin/tour_def/earth/ moons_and_rings.html ], and the absence of wind were an architectural boon allowing a much more slender and fragile-looking building than would have been possible on Earth [ http://www.bc.edu/bc_org/avp/cas/fnart/arch/ contents_europe.html ]. Illustrated here, the structure's two 160 meter high needle-like towers soar over [ http://www.rombaut.nl/engindex2.htm ] the rim of a deep canyon as planet Earth hangs in the lunar sky [ http://snoopy.gsfc.nasa.gov/~lunartel/ ]. To shield the interior, Rombaut designed 50 centimeter thick walls with two outer layers of Moon rock and a 35 centimeter layer of water [ http://nssdc.gsfc.nasa.gov/planetary/ice/ice_moon.html ] held between glass planes. The water absorbs energetic cosmic rays [ http://www.hps.org/ publicinformation/ate/q753.html ] and along with the rock helps keep the temperature constant. Windows are framed as holes in the rock layers. Construction materials [ http://www.seds.org/~rme/lunar.html ] are intended to be manufactured on the Moon [ http://lunar.arc.nasa.gov/ ] itself. This Moon Hotel design is welcomed by the international Lunar Explorers Society, LUNEX [ http://www.lunarexplorers.org ], who hope to construct a robotic Moon base [ http://ads.harvard.edu/books/lbsa/ ] by 2015, ultimately [ http://members.aol.com/dsfportree/explore.htm ] supporting a lunar village by 2040. |
|
Phobos: Doomed Moon of Mars
| Title |
Phobos: Doomed Moon of Mars |
| Explanation |
Mars [ http://mars.jpl.nasa.gov/extreme/index.html ], the red planet named for the Roman god of war, has two tiny moons, Phobos [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ phobos.html ] and Deimos [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ deimos.html ], whose names are derived from the Greek for Fear and Panic. These Martian moons [ http://www.seds.org/billa/tnp/hypo.html#mars ] may well be captured asteroids [ http://www.seasky.org/solarsystem/sky3k.html ] originating in the main asteroid belt between Mars and Jupiter [ http://www.jpl.nasa.gov/galileo/jupiter/ jupiter.html ] or perhaps from even more distant reaches of the Solar System [ http://space.jpl.nasa.gov/ ]. In this 1978 Viking 1 orbiter image [ http://nssdc.gsfc.nasa.gov/photo_gallery/caption/ vik_phobos_caption.html ], the largest moon, Phobos [ http://seds.lpl.arizona.edu/nineplanets/ nineplanets/phobos.html ], is indeed seen to be a heavily cratered asteroid-like object. About 17 miles across, Phobos really zips [ http://antwrp.gsfc.nasa.gov/apod/ap991105.html ] through the Martian sky. Actually rising above Mars' western horizon and setting in the east, it completes an orbit in less than 8 hours. But Phobos is doomed. Phobos orbits so close to Mars, (about 3,600 miles above the surface compared to 250,000 miles for our Moon [ http://antwrp.gsfc.nasa.gov/apod/ap010127.html ]) that gravitational tidal forces are dragging it down. In 100 million years or so it will likely crash into the surface or be shattered by stress caused by the relentless tidal forces [ http://www.badastronomy.com/bad/misc/tides.html ], the debris forming a ring around Mars. |
|
Jagged Hills on Jupiter's Ca
…
| Title |
Jagged Hills on Jupiter's Callisto |
| Explanation |
Why does Jupiter's moon Callisto have unusual jagged hills? This mystery came to light after the robot spacecraft [ http://galileo.jpl.nasa.gov/mission/space-intro.html ] Galileo [ http://galileo.jpl.nasa.gov/mission/mission.html ], in orbit around Jupiter [ http://www.nineplanets.org/jupiter.html ] since 1995, swooped past the dark moon [ http://antwrp.gsfc.nasa.gov/apod/ap980512.html ] in May. The resulting pictures [ http://www.jpl.nasa.gov/images/callisto/callisto_terrain_caption.html ] were the highest resolution yet obtained for a Jovian moon [ http://galileo.jpl.nasa.gov/moons/moons.html ]: objects as small as 3 meters across are discernable. The strange landscapes pictured above [ http://antwrp.gsfc.nasa.gov/apod/ap010828.html http://galileo.jpl.nasa.gov/news/release/press010822.html ] show areas rich in bright sharp mounds about 100 meters tall. A likely formation hypothesis [ http://galileo.jpl.nasa.gov/news/release/press010822.html ] holds that these hills are the result of ejecta thrown billions of years ago during a violent impact [ http://antwrp.gsfc.nasa.gov/apod/ap990711.html ]. The lower inset region apparently has undergone an epoch of relatively high ice-erosion [ http://members.edventures.com/terms/e/erosion/definition.html ], where dark rock has filled in some of the inter-hill regions. NASA [ http://www.nasa.gov/ ] has recently cleared Galileo [ http://galileo.jpl.nasa.gov/news/release/press010315.html ] to continue swooping Jupiter's moons [ http://www.sciam.com/2000/0200issue/0200johnson.html ] until 2003, when it will end its journey [ http://galileo.jpl.nasa.gov/news/release/press010315.html ] with a spectacular dive [ http://antwrp.gsfc.nasa.gov/apod/ap951208.html ] into Jupiter's atmosphere [ http://antwrp.gsfc.nasa.gov/apod/ap000429.html ]. |
|
Moon Occults Saturn
| Title |
Moon Occults Saturn |
| Explanation |
On September 18, 1997, many stargazers in the U. S. [ http://antwrp.gsfc.nasa.gov/apod/ap000708.html ] were able to watch a lovely early morning lunar occultation [ http://www.skypub.com/sights/occultations/occultations.shtml ] as a bright Moon [ http://jrscience.wcp.muohio.edu/lab/MoonLab.html ] passed in front of Saturn. Using a 1.2 meter reflector [ http://cfa-www.harvard.edu/cfa/oir/FLWO/FLWO/48/48.html ], astronomer Kris Stanek had an excellent view of this [ http://cfa-www.harvard.edu/~kstanek/Saturn/ ] dream-like event from the Whipple Observatory [ http://linmax.sao.arizona.edu/help/FLWO/whipple.html ] atop Arizona's Mount Hopkins [ http://cfa-www.harvard.edu/flwo/visitcenter.html ]. This animated gif image was constructed by Wes Colley from 4 frames taken by Stanek at 35 second intervals as the ringed planet emerged from behind the Moon's [ http://antwrp.gsfc.nasa.gov/apod/ap970916.html ] dark limb. While lunar occultations [ http://www.skypub.com/sights/occultations/lunar/ 0101lunarocc.html ] of fairly bright stars and planets are not extremely rare events, their exact timing [ http://www.lunar-occultations.com/iota/iotandx.htm ] depends critically on the observer's location. For observers in western North America [ http://www.lunar-occultations.com/iota/0910sat.htm ], the Moon will next occult Saturn on Monday morning, September 10 [ http://www.lunar-occultations.com/iota/0910sat.htm ]. |
|
Moon AND Stars
| Title |
Moon AND Stars |
| Explanation |
Here's something you don't see too often ... a detailed picture of the full Moon surrounded by a rich field of background stars. It's true that bright moonlight scattered by the atmosphere tends to mask faint stars, but pictures of the sunlit portion [ http://aa.usno.navy.mil/faq/docs/moon_phases.html ] of the Moon made with earthbound [ http://antwrp.gsfc.nasa.gov/apod/ap010428.html ] telescopes or even with cameras on the lunar surface [ http://antwrp.gsfc.nasa.gov/apod/ap001209.html ] often fail to show any background stars at all [ http://www.badastronomy.com/bad/tv/ foxapollo.html#stars ]. Why? Because the exposure times are too short. Very short exposures, lasting fractions of a second, are required to accurately record an image [ http://www.u-net.com/ph/mas/observe/lunar-p/lunar-p.htm ] of the bright lunar surface. But the background stars (and galaxies!) such as those visible above are much fainter and need exposures lasting minutes to hours which would seriously overexpose [ http://antwrp.gsfc.nasa.gov/apod/ap010209.html ] the surface of the Moon. So, of course this stunning view [ http://www.noao.edu/image_gallery/html/ im0650.html ] really is a combination of two digital images -- a short exposure, registering the exquisite lunar surface details at full Moon [ http://antwrp.gsfc.nasa.gov/apod/ap010809.html ], superposed on a separate very long exposure, made with the Moon [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ luna.html ] absent from the star field. The final representation of Moon [ http://www.lhl.lib.mo.us/pubserv/hos/moon/frontisp.htm ] and background stars is very dramatic, even though it could not have been captured in a single exposure. |
|
VERITAS and Venus
| Title |
VERITAS and Venus |
| Explanation |
Early morning risers and late to bed astronomers have recently enjoyed bright planets [ http://science.nasa.gov/headlines/y2007/02nov_nov5.htm ] in predawn skies, with brilliant Venus [ http://www.avertedimagination.com/img_pages/ morning_star.html ] above the eastern horizon. On November 5, Venus was joined by the waning crescent Moon. This self-portrait by astronomer Larry Ciupik captures the lovely pairing of the two brightest celestial beacons on the scene, though the Moon, right of Venus, is strongly over exposed. Included at the far left in the 30 second exposure is the bright streak of the International Space Station [ http://antwrp.gsfc.nasa.gov/apod/ap070625.html ] still docked with shuttle orbiter Discovery [ http://www.nasa.gov/mission_pages/shuttle/ main/index.html ]. Together in Earth orbit, the spacefaring [ http://antwrp.gsfc.nasa.gov/apod/ap070628.html ] combination was momentarily the third brightest sky light in view [ http://spaceflight.nasa.gov/realdata/sightings/index.html ]. In dim silhouette, a multi-mirrored unit of the Very Energetic Radiation Imaging Telescope Array System (VERITAS [ http://veritas.adlerplanetarium.org/home.shtml ]) is also visible in the foreground. VERITAS operates at the Whipple Observatory near Tucson, Arizona to detect high-energy gamma-rays from the cosmos [ http://veritas.adlerplanetarium.org/science/ ]. |
|
Pluto: New Horizons
| Title |
Pluto: New Horizons |
| Explanation |
Pluto's [ http://dosxx.colorado.edu/plutohome.html ] horizon spans the foreground in this artist's vision, gazing sunward across that distant and not yet explored [ http://antwrp.gsfc.nasa.gov/apod/ap960212.html ] world. Titled New Horizons, the painting also depicts Pluto's [ http://maps.jpl.nasa.gov/pluto.html ] companion, Charon [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ pluto.html#charon ], as a darkened, ghostly apparition with a luminous crescent [ http://www.lowell.edu/users/buie/pluto/chphases.html ] against a starry background. Beyond Charon [ http://www.jpl.nasa.gov/ice_fire/CharonDiscovery.htm ], the diminished Sun is immersed in a flattened cloud of zodiacal dust [ http://antwrp.gsfc.nasa.gov/apod/ap010912.html ]. Here, Pluto's ruddy colors are based on existing astronomical [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query? bibcode=2000DPS....32.4601Y ] observations while imagined but scientifically [ http://adsabs.harvard.edu/cgi-bin/nph-bib_query? bibcode=1999AJ....117.1063Y ] tenable details provided by the artist include high atmospheric cirrus and dark plumes from surface vents, in analogy to Neptune's large moon Triton [ http://antwrp.gsfc.nasa.gov/apod/ap950805.html ] explored by the Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager_fs.html ] 2 spacecraft in 1989. Craters suggest bombardment by Kuiper Belt [ http://www.ifa.hawaii.edu/faculty/jewitt/kb.html ] objects, a newly understood population of [ http://www.solstation.com/stars/kuiper.htm ] outer solar system bodies likely related to [ http://antwrp.gsfc.nasa.gov/apod/ap010830.html ] the Pluto-Charon system [ http://www.jpl.nasa.gov/ice_fire//alans.htm ]. NASA is now considering a future robotic reconnaissance mission to [ ftp://ftp.hq.nasa.gov/pub/pao/pressrel/2001/01-114.txt ] Pluto-Charon and the Kuiper Belt which could reach the distant worlds late in the next decade. |
|
Mars in View
| Title |
Mars in View |
| Explanation |
Very good telescopic views of Mars [ http://mars.jpl.nasa.gov/allabout/nightsky/ viewing-tips-2007.html ] can be expected in the coming weeks as the Red Planet [ http://www.uapress.arizona.edu/onlinebks/mars/contents.htm ] nears opposition on December 24th. Of course [ http://antwrp.gsfc.nasa.gov/apod/ap060422.html ], opposition means opposite the Sun in planet Earth's sky - an arrangement [ http://mars.jpl.nasa.gov/allabout/nightsky/nightsky03.html ] that occurs every 26 months for Mars. Because of Mars' [ http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html ] more elliptical orbit, the actual date of closest approach to Earth will be December 18, when Mars will be within about 88 million kilometers of our fair planet. Situated in the constellation Gemini and rising after evening twilight, the bright, ruddy disk of Mars will reach nearly 16 arcseconds [ http://coolcosmos.ipac.caltech.edu/cosmic_classroom/ cosmic_reference/angular.html ] in diameter (about 1/100th the diameter of the Full Moon). In this already exceptional image taken on November 18, north is down and surface markings around the sprawling, dark, albedo feature Syrtis Major [ http://photojournal.jpl.nasa.gov/catalog/PIA01592 ] are remarkably clear. The image was recorded with a video camera and filters on a 1 meter telescope at Pic Du Midi [ http://en.wikipedia.org/wiki/Pic_du_Midi_de_Bigorre ], a mountain top observatory in the French Pyrenees. NASA launched the Phoenix [ http://phoenix.lpl.arizona.edu/mission.php ] lander to Mars in August, scheduled to arrive in May 2008. |
|
A Newly Active Volcano on Ju
…
| Title |
A Newly Active Volcano on Jupiter's Io |
| Explanation |
Would a volcano plume discovered in January above Jupiter's Moon Io still be active months later? To answer this question, the robot spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/overview.html ] currently in orbit around Jupiter [ http://www.nineplanets.org/jupiter.html ] was maneuvered to image the plume [ http://antwrp.gsfc.nasa.gov/apod/ap970818.html ] site during its recent flyby of Io [ http://www.nineplanets.org/io.html ] in August. What was found was the highest volcano plume yet discovered [ http://www.jpl.nasa.gov/images/io/caption_ioplume_1004.html ] -- but above a completely different and previously undocumented volcano! The original plume [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02584 ], above the Tvashtar Catena [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02550 ] volcanic area, was not even visible. A picture taken in January [ http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA02588 ] of the area surrounding the Tvashtar Catena eruption is shown above in enhanced color, with a new picture taken in August [ http://www.jpl.nasa.gov/images/io/caption_ioplume_1004.html ] shown in the inset. Careful inspection of the two images will show a newly prominent dark volcano [ http://antwrp.gsfc.nasa.gov/apod/ap991126.html ] surrounded by a light-colored ring visible only in the smaller, more recent image [ http://www.jpl.nasa.gov/releases/2001/release_2001_192.html ]. |
|
Asteroid 2007 TU24 Passes th
…
| Title |
Asteroid 2007 TU24 Passes the Earth |
| Explanation |
Asteroid 2007 TU24 passed by the Earth yesterday, posing no danger. The space rock, estimated [ http://www.nasa.gov/topics/solarsystem/features/asteroid-20080125.html ] to be about 250 meters across, coasted by just outside the orbit of Earth's Moon. The passing was not very unusual [ http://antwrp.gsfc.nasa.gov/apod/ap050417.html ] -- small rocks strike Earth daily, and in 2003 a rock the size of a bus passed inside the orbit of the Moon, being detected only after passing [ http://antwrp.gsfc.nasa.gov/apod/ap031015.html ]. TU24 was notable partly because it was so large. Were TU24 [ http://en.wikipedia.org/wiki/TU24 ] to have struck land, it might have caused a magnitude [ http://www.geo.mtu.edu/UPSeis/magnitude.html ] seven earthquake [ http://www.youtube.com/watch?v=19fMs633Td4 ] and left a city-sized crater [ http://antwrp.gsfc.nasa.gov/apod/ap990711.html ]. A perhaps larger danger would have occurred were TU24 [ http://www.planetary.org/blog/article/00001309/ ] to have struck the ocean and raised a large tsunami [ http://en.wikipedia.org/wiki/Tsunami ]. This radar image [ http://www.jpl.nasa.gov/news/news.cfm?release=2008-014 ] was taken two days ago. The Arecibo Radio Telescope [ http://antwrp.gsfc.nasa.gov/apod/ap981129.html ] in Puerto Rico [ http://en.wikipedia.org/wiki/Puerto_Rico ] broadcast radar that was reflected by the asteroid and then recorded by the Byrd Radio Telescope [ http://www.gb.nrao.edu/gbt/ ] in Green Bank [ http://www.nrao.edu/administration/personnel_office/greenbank.shtml ], West Virginia [ http://en.wikipedia.org/wiki/West_Virginia ]. The resulting image [ http://www.jpl.nasa.gov/news/news.cfm?release=2008-014 ] shows TU24 to have an oblong and irregular shape. TU24 [ http://www.nasa.gov/topics/solarsystem/features/asteroid-20080128-clips.html ] was discovered only three months ago, indicating that other potentially hazardous asteroids [ http://neo.jpl.nasa.gov/ca/ ] might lurk in our Solar System [ http://space.jpl.nasa.gov/ ] currently undetected. Objects like TU24 [ http://www.space.com/scienceastronomy/080128-asteroid-radar.html ] are hard to detect because they are so faint and move [ http://antwrp.gsfc.nasa.gov/apod/ap060328.html ] so fast. Humanity's ability to scan the sky to detect, catalog, and analyze such objects has increased notably [ http://www.lpl.arizona.edu/css/ ] in recent years. |
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Moon Struck
| Title |
Moon Struck |
| Explanation |
Craters produced by ancient impacts on the airless Moon [ http://antwrp.gsfc.nasa.gov/apod/ap990326.html ] have long been a familiar sight [ http://antwrp.gsfc.nasa.gov/apod/ap010428.html ]. But only since 1999 have observers seen elusive optical flashes on the lunar surface [ http://science.nasa.gov/headlines/y2001/ ast30nov_1.htm ] - likely explosions resulting from impacting meteoroids. These startling observations were made [ http://iota.jhuapl.edu/leo01n26.htm ] with modest telescopes and video equipment during the 1999 and 2001 Leonid meteor showers. Six confirmed flashes, some initially as bright as a third magnitude star, were all seen within hours of the peak of the 1999 shower. At least two more lunar flashes [ http://www.lpl.arizona.edu/~rhill/alpo/lunarstuff/ impactalert.html ], the brightest one at about fourth magnitude, have been confirmed [ http://homepage.mac.com/dmpalmer/webpage/ Candidates.html ] during this November's Leonid storm [ http://antwrp.gsfc.nasa.gov/apod/ap011130.html ]. The 1999 locations [ http://antwrp.gsfc.nasa.gov/apod/ap991208.html ] are indicated by the red Xs on the dark lunar night side in this projection of the Moon from November 18 of that year. Similar flashes would have been difficult to see if viewed [ http://www.boulder.swri.edu/~durda/Apollo/landing_sites.html ] against the Moon's [ http://www.inconstantmoon.com/ ] brightly lit portion. It is estimated that the flashes were made by meteoroids with masses in the range of 1 to 10 kilograms, producing craters a few meters across. |
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Ski Enceladus
| Title |
Ski Enceladus |
| Explanation |
A small inner moon of Saturn [ http://csep10.phys.utk.edu/astr161/lect/saturn/moons.html ], Enceladus is only about 500 kilometers in diameter. But the cold, distant world does reflect over 90 percent of the sunlight it receives, giving its surface about the same reflectivity as new-fallen snow. Seen here [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA00347 ] in a mosaic of Voyager [ http://vraptor.jpl.nasa.gov/voyager/ vgrsat_fs.html ] 2 images from 1981, Enceladus [ http://solarsystem.nasa.gov/features/planets/saturn/ enceladus.html ] shows a variety of surface features and very few impact craters - indicating that it is an active world even though this ice moon should have completely cooled off long ago [ http://www.sciam.com/explorations/010697sagan/ 010697sagan1.html ]. In fact the fresh, resurfaced appearance of Enceladus suggests that an internal mechanism, perhaps driven by tidal pumping, generates heat and supplies liquid water to geysers or water volcanos [ http://pirlwww.lpl.arizona.edu/HIIPS/ Cryovolcanism/ ]. Since Enceladus orbits within the tenuous outer E [ http://www.astro.spbu.ru/staff/dikarev/valery/ering.html ] ring [ http://ringmaster.arc.nasa.gov/saturn/ saturn.html#IMAGES ] of Saturn, the moon's surface may be kept snow-bright as it is continuously bombarded with icy ring particles. Eruptions [ http://www.jpl.nasa.gov/cassini/Mission/pix/ enceladus_lg.gif ] on Enceladus itself would in turn supply material to the E ring. Interplanetary [ http://www.jpl.nasa.gov/cassini/Mission/ ] ski [ http://antwrp.gsfc.nasa.gov/apod/ap990401.html ] bums take note: tiny Enceladus has only about one hundredth the surface gravity of planet Earth [ http://photojournal.jpl.nasa.gov/cgi-bin/ PIAGenCatalogPage.pl?PIA03439 ]. |
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Neptune: Big Blue Giant
| Title |
Neptune: Big Blue Giant |
| Explanation |
This picture was taken by the Voyager 2 [ http://nssdc.gsfc.nasa.gov/planetary/voyager.html ] spacecraft in 1986 - the only spacecraft ever to visit Neptune. Neptune [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/neptune.html ] will be the farthest planet from the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ] until 1999, when the elliptical orbit of Pluto will cause it to once again resume this status. Neptune [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/neptune.html ], like Uranus [ http://antwrp.gsfc.nasa.gov/apod/ap950816.html ], is composed mostly of liquid water, methane and ammonia, is surrounded by a thick gas atmosphere of mostly hydrogen and helium, and has many moons and rings. Neptune [ http://nssdc.gsfc.nasa.gov/photo_gallery/photogallery-neptune.html ]'s moon Triton [ http://antwrp.gsfc.nasa.gov/apod/ap950805.html ] is unlike any other and has active volcanoes. The nature of Triton [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/triton.html ]'s unusual orbit around Neptune is the focus of much discussion and speculation. Tomorrow's picture: Pluto: The Frozen Planet |
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Comet Ikeya-Zhang
| Title |
Comet Ikeya-Zhang |
| Explanation |
Comet Ikeya-Zhang [ http://cometography.com/lcomets/2002c1.html ] is presently heading north in planet Earth's sky [ http://encke.jpl.nasa.gov/images/02C1/ c2002c1chart.jpg ], framed by stars of the constellation Cetus. The comet was discovered [ http://cfa-www.harvard.edu/iauc/07800/ 07812.html ] as a faint, telescopic object [ http://encke.jpl.nasa.gov/RecentObs.html#02C1 ] near the western horizon on the evening of February 1st independently by Kaoru Ikeya [ http://comets.amsmeteors.org/comets/ lcomets/1965s1.html ] of Shizuoka prefecture, Japan, Daqing Zhang in Henan province, China, and later by [ http://cfa-www.harvard.edu/iauc/07800/07813.html ] observer Paulo Raymundo of Salvador, Brazil. But Ikeya-Zhang [ http://skyandtelescope.com/observing/objects/comets/ article_477_1.asp ] is expected to brighten significantly and in March and April could become visible to the unaided eye. This picture, taken near Tucson, Arizona, USA on the evening of February 9th, covers a field a bit less than the width of the full moon showing the comet's [ http://encke.jpl.nasa.gov/define.html ] condensed coma [ http://www.ifa.hawaii.edu/faculty/jewitt/ coma.html ] and narrow, developing tail [ http://antwrp.gsfc.nasa.gov/apod/ap001227.html ]. Ikeya-Zhang should pass closest to the Sun (perihelion) on March 18 at a point roughly midway [ http://encke.jpl.nasa.gov/images/02C1/ ikeyaorbit.jpg ] between the orbits of Mercury and Venus. Based on preliminary calculations of this comet's orbit, Ikeya-Zhang [ http://cfa-www.harvard.edu/iau/Ephemerides/Comets/ 2002C1.html ] is suspected of being a periodic comet, returning to the inner Solar System every 500 years or so. In fact, it is "speculated" that Ikeya-Zhang may be directly connected with a historic bright comet [ http://ssd.jpl.nasa.gov/great_comets.html ] seen in 1532. |
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Pluto: The Frozen Planet
| Title |
Pluto: The Frozen Planet |
| Explanation |
The Hubble Space Telescope imaged [ http://www.ast.cam.ac.uk/HST/press/pluto.html ] Pluto and its moon Charon in 1994. Pluto [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/pluto.html ] is usually the most distant planet from the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ] but because of its elliptic orbit Pluto crossed inside of Neptune [ http://antwrp.gsfc.nasa.gov/apod/ap950817.html ]'s orbit in 1979 and will cross back out again in 1999. Compared to the other planets, very little is known about Pluto. Pluto [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/pluto.html ] is smaller than any other planet and even smaller than several other planet's moons. From Pluto, the Sun is just a tiny point of light. Pluto [ http://dosxx.colorado.edu/plutohome.html ] is probably composed of frozen rock and ice, much like Neptune's moon Triton [ http://antwrp.gsfc.nasa.gov/apod/ap950805.html ]. Pluto has not yet been visited by a spacecraft, but a mission [ http://www.jpl.nasa.gov/pluto/ ] is being planned for the next decade. Tomorrow's picture: Our Solar System from Voyager |
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Venus: Earth's Sister Planet
| Title |
Venus: Earth's Sister Planet |
| Explanation |
This picture in visible light was taken by the Galileo [ http://nssdc.gsfc.nasa.gov/planetary/galileo.html ] spacecraft. Venus [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/venus.html ] is very similar to Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950622.html ] in size and mass - and so is sometimes referred to as Earth's sister planet - but Venus has a quite different climate. Venus' [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/venus.html ] thick clouds and closeness to the Sun [ http://antwrp.gsfc.nasa.gov/apod/ap950813.html ] (only Mercury [ http://antwrp.gsfc.nasa.gov/apod/ap950814.html ] is closer) make it the hottest planet - much hotter than the Earth. Humans could not survive there, and no life of any sort has ever been found. When Venus [ http://nssdc.gsfc.nasa.gov/photo_gallery/PhotoGallery-Venus.html ] is visible it is usually the brightest object in the sky after the Sun and the Moon. More than 20 spacecraft have visited Venus including Venera 9, which landed on the surface, and Magellan [ http://stardust.jpl.nasa.gov/mveg/guide.html ], which used radar to peer through the clouds and make a map of the surface. There are still many things about Venus's unusual atmosphere that astronomers don't understand. Tomorrow's picture: Uranus: The Tilted Planet |
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Jupiter's Great X-Ray Spot
| Title |
Jupiter's Great X-Ray Spot |
| Explanation |
The Solar System's largest planet, gas giant Jupiter [ http://www.windows.ucar.edu/tour/link=/jupiter/discovery.html ], is famous for its swirling Great Red Spot [ http://heritage.stsci.edu/1999/29/index.html ]. In the right hand panel above, the familiar giant planet with storm system and cloud bands [ http://antwrp.gsfc.nasa.gov/apod/ap010215.html ] is shown in an optical image from the passing Cassini spacecraft [ http://www.jpl.nasa.gov/jupiterflyby/ ]. In the left hand panel, a false-color image from the orbiting [ http://chandra.harvard.edu/about/tracking.html ] Chandra Observatory [ http://chandra.harvard.edu/about/axaf_mission.html ] presents a corresponding x-ray view of Jupiter. The Chandra image [ http://chandra.harvard.edu/photo/2002/0001/ index.html ] shows clearly, for the first time, x-ray spots and auroral x-ray emission from the poles [ http://antwrp.gsfc.nasa.gov/apod/ap001219.html ]. The x-ray spot dominating the emission from Jupiter's north pole [ http://antwrp.gsfc.nasa.gov/apod/ap010201.html ] (top) is perhaps as surprising for astronomers today as the Great Red Spot once was [ http://www.seds.org/messier/xtra/Bios/cassini.html ]. Confounding previous theories [ http://chandra.harvard.edu/press/02_releases/ press_022702.html ], the x-ray spot is too far north to be associated with heavy electrically charged particles from the vicinity [ http://xxx.lanl.gov/abs/astro-ph/0202277 ] of volcanic moon Io [ http://antwrp.gsfc.nasa.gov/apod/ap981016.html ]. Chandra data also show that the spot's x-ray [ http://chandra.harvard.edu/xray_astro/xrays.html ] emission mysteriously pulsates over a period of about 45 minutes. |
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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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Europa: Ancient Water World
| Title |
Europa: Ancient Water World |
| Explanation |
Beneath the cold icy surface of Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ]'s moon Europa [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/europa.html ] are probably the only oceans of water in our Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ] outside of Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950622.html ]. These oceans, possibly 50 kilometers deep, might also be the most likely local place to find extra-terrestrial life. Europa [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/europa.html ]'s smooth surface is unlike any other known planet or moon, giving evidence for relatively few craters or mountains. Europa was discovered by Galileo [ http://galileo.imss.firenze.it/museo/4/index.html ] and Marius [ http://seds.lpl.arizona.edu/billa/tnp/help.html#M ] in 1610. The NASA spacecraft Galileo [ http://www.jpl.nasa.gov/galileo/ ] is scheduled to arrive at Jupiter in December of 1995. Tomorrow's picture: Callisto: Dark Smashed Iceball |
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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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One Small Step
| Title |
One Small Step |
| Explanation |
On July 20th, 1969, a human first set foot on the Moon [ http://antwrp.gsfc.nasa.gov/apod/ap950903.html ]. Pictured above is the first lunar footprint. The footprint and distinction of the first person to walk on the Moon [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/luna.html ] belong to Neil Armstrong. It has been estimated that one billion people world-wide watched Armstrong's first step - making the live transmission from a camera mounted on the lunar lander the highest rated television show ever. Upon setting foot on the moon, Armstrong said: "That's one small step for (a) man, one giant leap for mankind." [ gopher://www.ksc.nasa.gov:70/ss/history/apollo/ apollo-11/sounds/A01106AA ] The Apollo missions [ http://www.ksc.nasa.gov/history/apollo/apollo.html ] to the Moon [ http://www.nasm.edu/APOLLO/AS11/Apollo11_fact.html ] have been described as the result of the greatest technological mobilization the world has known. |
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Saturn's Moon Dione
| Title |
Saturn's Moon Dione |
| Explanation |
Dione [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/dione.html ], one of Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950705.html ]'s larger moons, is remarkable for its bright surface streaks. These streaks run across some of Dione's many craters, which indicate that the process which created the streaks occurred later than the process which created the craters. Dione [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/dione.html ] is made of mostly water ice but its relatively high density indicates that it contains much rock inside. Dione was discovered by Giovanni Cassini in 1684. NASA's Cassini mission [ http://newproducts.jpl.nasa.gov/calendar/cassini.html ] to Saturn is currently scheduled for launch in October 1997. Dione's orbit is remarkable it that it also houses the much smaller moon Helene [ http://antwrp.gsfc.nasa.gov/apod/ap951010.html ]. This moon, once designated "Dione B", precedes Dione by about 1/6th of an orbit. |
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Titan: Saturn's Smog Moon
| Title |
Titan: Saturn's Smog Moon |
| Explanation |
The largest moon of Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950705.html ] is a rare wonder. Titan is the only one of Saturn [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/titan.html ]'s moons with an atmosphere, and one of only two moons in the Solar System [ http://antwrp.gsfc.nasa.gov/apod/ap950819.html ] with this distinction (Neptune [ http://antwrp.gsfc.nasa.gov/apod/ap950817.html ]'s Triton [ http://antwrp.gsfc.nasa.gov/apod/ap950805.html ] is the other). Titan [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/titan.html ]'s thick cloudy atmosphere is mostly nitrogen, like Earth [ http://antwrp.gsfc.nasa.gov/apod/ap950622.html ]'s, but contains much higher percentages of "smog-like" chemicals such as methane and ethane. The smog may be so thick that it actually rains "gasoline-like" liquids. The organic nature of some of the chemicals found in Titan's atmosphere cause some to speculate that Titan may harbor life! Because of its thick cloud cover, however, Titan's actual surface properties remain mysterious. Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager.html ] 1 flew by in 1980 taking the above picture, and recently much has been learned from Hubble Space Telescope observations [ http://www.stsci.edu/pubinfo/PR/94/55.html ]. The Cassini mission [ http://www.jpl.nasa.gov/mip/cassini.html ] currently scheduled for launch in 1997 will map Titan's surface, helping to solve some of its mysteries. |
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Deimos: A Small Martian Moon
| Title |
Deimos: A Small Martian Moon |
| Explanation |
Mars [ http://antwrp.gsfc.nasa.gov/apod/ap950721.html ] has two tiny moons, Phobos [ http://antwrp.gsfc.nasa.gov/apod/ap951002.html ] and Deimos. Pictured above is Deimos [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/deimos.html ], the smallest moon of Mars [ http://stardust.jpl.nasa.gov/planets/welcome/mars.htm ]. In fact, Deimos is the smallest known moon [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/ datamax.html#smallest ] in the Solar System measuring only 9 miles across. The diminutive Martian moons were discovered in 1877 by Asaph Hall [ http://www.usno.navy.mil/histnots.html ], an American astronomer working at the US Naval Observatory [ http://www.usno.navy.mil/ ] in Washington D.C. The existence of two Martian moons was predicted around 1610 by Johannes Kepler [ http://www.seds.org/billa/tnp/help.html#kepler ], the astronomer who derived the laws of planetary motion. In this case, Kepler's prediction [ http://www.seds.org/billa/tnp/hypo.html#mars ] was not based on scientific principles, but his writings and ideas were so influential that the two Martian moons are discussed in works of fiction such as Jonathan Swift's "Gulliver's Travels" [ gopher://gopher.vt.edu:10010/02/146/1 ], written in 1726, over 150 years before their actual discovery. |
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Mimas: Small Moon with A Big
…
| Title |
Mimas: Small Moon with A Big Crater |
| Explanation |
Mimas [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/mimas.html ] is one of the smaller moons of Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950705.html ] but shows one of the largest impact craters! In fact, if the impact had been much greater, it would have disrupted the entire satellite. The large crater has been named Herschel after the 1789 discoverer of Mimas, Sir William Herschel [ http://star.arm.ac.uk/history/herschel.html ]. Mimas' low mass produces a surface gravity just strong enough to create a spherical body but weak enough to allow such relatively large surface features. Mimas [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/mimas.html ] is made of mostly water ice with a smattering of rock - so it is accurately described as a big dirty snowball. Voyager [ http://vraptor.jpl.nasa.gov/voyager/voyager.html ] 1 flew by in 1980 and took the above picture. |
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Dione's Lagrange Moon Helene
| Title |
Dione's Lagrange Moon Helene |
| Explanation |
Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950705.html ]'s moon Helene [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/helene.html ] is very unusual in that it circles Saturn [ http://antwrp.gsfc.nasa.gov/apod/ap950801.html ] near the orbit of a bigger moon: Dione [ http://antwrp.gsfc.nasa.gov/apod/ap951009.html ]. Helene is situated in what is called a "Lagrange point" of Dione - a place of stability created by Dione's gravity. Were Helene [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/dione.html#helene ] to stray slightly from its orbit 1/6 ahead of Dione, the larger moon's gravity would cause Helene to move back toward the Lagrange point. Many massive orbital bodies have stable Lagrange points, including the Earth and Moon. Helene was discovered from the ground by P. Laques & J. Lecacheux in 1980. The photograph above was taken by Voyager 2 as it passed Saturn in 1981. NASA's Cassini [ http://newproducts.jpl.nasa.gov/calendar/cassini.html ] mission to Saturn is currently scheduled for launch in October 1997. |
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Jupiter's Moon Amalthea
| Title |
Jupiter's Moon Amalthea |
| Explanation |
Amalthea is Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap951013.html ]'s fifth largest moon, much smaller than the four Galilean [ http://bang.lanl.gov/video/stv/arshtml/arstoc.html ] satellites Io [ http://antwrp.gsfc.nasa.gov/apod/ap950803.html ], Europa [ http://antwrp.gsfc.nasa.gov/apod/ap950905.html ], Ganymede [ http://antwrp.gsfc.nasa.gov/apod/ap950904.html ], and Callisto [ http://antwrp.gsfc.nasa.gov/apod/ap950906.html ]. The orbit of Amalthea [ http://seds.lpl.arizona.edu/nineplanets/nineplanets/amalthea.html#amalthea ] is inside of these moons, and with its long axis always pointing toward Jupiter [ http://antwrp.gsfc.nasa.gov/apod/ap950625.html ]. It's dark surface color is probably due to sulfur being expelled from Io [ http://antwrp.gsfc.nasa.gov/apod/ap950804.html ]. Amalthea is not massive enough for its internal gravity to make it spherical. Amalthea [ http://www.c3.lanl.gov/~cjhamil/SolarSystem/amalthea.html ] was discovered in 1892 by Edward Barnard. |
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