One moment in an ancient, orbital dance is caught in this color picture taken by NASA's Cassini spacecraft on Dec. 7, 2000, just as two of Jupiter's four major moons, Europa and Callisto, were nearly perfectly aligned with each other and the center of the planet. The distances are deceiving. Europa, seen against Jupiter, is 600,000 kilometers (370,000 miles) above the planet's cloud tops. Callisto, at lower left, is nearly three times that distance from the cloud tops. Europa is a bit smaller than Earth's Moon and has one of the brightest surfaces in the solar system. Callisto is 50 percent bigger -- roughly the size of Saturn's largest satellite, Titan -- and three times darker than Europa. Its brightness had to be enhanced in this picture, relative Europa's and Jupiter's, in order for Callisto to be seen in this image. Europa and Callisto have had very different geologic histories but share some surprising similarities, such as surfaces rich in ice. Callisto has apparently not undergone major internal compositional stratification, but Europa's interior has differentiated into a rocky core and an outer layer of nearly pure ice. Callisto's ancient surface is completely covered by large impact craters: The brightest features seen on Callisto in this image were discovered by the Voyager spacecraft in 1979 to be bright craters, like those on our Moon. In contrast, Europa's young surface is covered by a wild tapestry of ridges, chaotic terrain and only a handful of large craters. Recent data from the magnetometer carried by the Galileo spacecraft, which has been in orbit around Jupiter since 1995, indicate the presence of conducting fluid, most likely salty water, inside both Callisto and Europa. Scientists are eager to discover whether the surface of Saturn's Titan resembles that of Callisto or Europa, or whether it is entirely different, when Cassini finally reaches its destination in 2004. Cassini 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 Cassini mission for NASA's Office of Space Science, Washington, D.C. Credit: NASA/JPL/University of Arizona #####
Thick or Thin Ice Shell on E
…
title
Thick or Thin Ice Shell on Europa?
description
Scientists are all but certain that Europa has an ocean underneath its icy surface, but they do not know how thick this ice might be. This artist concept illustrates two possible cut-away views through Europa's ice shell. In both, heat escapes, possibly volcanically, from Europa's rocky mantle and is carried upward by buoyant oceanic currents. If the heat from below is intense and the ice shell is thin enough (left), the ice shell can directly melt, causing what are called "chaos" on Europa, regions of what appear to be broken, rotated and tilted ice blocks. On the other hand, if the ice shell is sufficiently thick (right), the less intense interior heat will be transferred to the warmer ice at the bottom of the shell, and additional heat is generated by tidal squeezing of the warmer ice. This warmer ice will slowly rise, flowing as glaciers do on Earth, and the slow but steady motion may also disrupt the extremely cold, brittle ice at the surface. Europa is no larger than Earth's moon, and its internal heating stems from its eccentric orbit about Jupiter, seen in the distance. As tides raised by Jupiter in Europa's ocean rise and fall, they may cause cracking, additional heating and even venting of water vapor into the airless sky above Europa's icy surface. (Artwork by Michael Carroll.) Credit: NASA/JPL
Europa Tide Movie
title
Europa Tide Movie
description
In this movie Europa is seen in a cutaway view through two cycles of its 3.5 day orbit about the giant planet Jupiter. + View Movie Like Earth, Europa is thought to have an iron core, a rocky mantle and a surface ocean of salty water. Unlike on Earth, however, this ocean is deep enough to cover the whole moon, and being far from the sun, the ocean surface is globally frozen over. Europa's orbit is eccentric, which means as it travels around Jupiter, large tides, raised by Jupiter, rise and fall. Jupiter's position relative to Europa is also seen to librate, or wobble, with the same period. This tidal kneading causes frictional heating within Europa, much in the same way a paper clip bent back and forth can get hot to the touch, as illustrated by the red glow in the interior of Europa's rocky mantle and in the lower, warmer part of its ice shell. This tidal heating is what keeps Europa's ocean liquid and could prove critical to the survival of simple organisms within the ocean, if they exist. Credit: NASA/JPL
Europa's Synthetic Subsurfac
…
Title
Europa's Synthetic Subsurface Heat Transport (Version 2)
Abstract
Encounters with Jupiter's moon Europa by the Voyager and Galileo spacecraft indicated that a liquid salty ocean might exist below a layer of surface ice that is up to 10 kilometers thick. An ocean general circulation model developed to study the earth's oceans was used to investigate the tidally-forced ocean circulations on Europa. The orbit of Europa is 'gravity locked' so that the same side of Europa always faces Jupiter as is the case with the earth's moon. The icy surface of Europa heaves up and down 50 meters due to the strong tidal forces. This visualization shows the temperature changes induced from the flow fields calculated for a European ocean 50 kilometers deep. The warmest temperatures tend to be near the equator, not because of heating by the sun, but because the currents in the European ocean move the warmest waters to that location. Understanding the thermal and flow fields from these model runs will help to interpret observations from future missions to Europa such as the Jupiter's Icy Moons Orbiter mission proposed for launch in 2012.
Completed
2004-05-04
Europa's Broken Ice
Jupiter's moon Europa, as se
…
Description
Jupiter's moon Europa, as seen in this image taken June 27, 1996 by NASA's Galileo spacecraft, displays features in some areas resembling ice floes seen in Earth's polar seas. Europa, about the size of Earth's moon, has an icy crust that has been severely fractured, as indicated by the dark linear, curved, and wedged- shaped bands seen here. These fractures have broken the crust into plates as large as 30 kilometers (18.5 miles) across. Areas between the plates are filled with material that was probably icy slush contaminated with rocky debris. Some individual plates were separated and rotated into new positions. Europa's density indicates that it has a shell of water ice as thick as 100 kilometers (about 60 miles), parts of which could be liquid. Currently, water ice could extend from the surface down to the rocky interior, but the features seen in this image suggest that motion of the disrupted icy plates was lubricated by soft ice or liquid water below the surface at the time of disruption. This image covers part of the equatorial zone of Europa and was taken from a distance of 156,000 kilometers (about 96,300 miles) by the solid-state imager camera on the Galileo spacecraft. North is to the right and the sun is nearly directly overhead. The area shown is about 360 by 770 kilometers (220-by-475 miles or about the size of Nebraska), and the smallest visible feature is about 1.6 kilometers (1 mile) across.
Europa: Sea Salts or Battery
…
This composite image of the
…
4/19/00
Date
4/19/00
Description
This composite image of the Jupiter-facing hemisphere of Europa was obtained on November 25, 1999 by two instruments onboard NASA's Galileo spacecraft. The global black-and-white view, by the spacecraft's camera, provides the highest resolution view ever obtained of this side of Europa. The superimposed false-color image, obtained by Galileo's near-infrared mapping spectrometer instrument, reveals the presence of materials with differing compositions on Europa's surface. In this image, blue areas represent the cleanest, brightest icy surfaces, while the reddest areas have the highest concentrations of darker, non-ice materials. The mixture of colors seen here is most likely the result of both variations in the ages and composition of surface materials. The dark materials are believed to fade with the passage of time. This area is highly unusual compared to many other areas on Europa because of its high concentration of fresh-appearing bright ridges and fractures. On other parts of Europa, the darker areas appear to be the most recently formed, but here the ridges and fractures appear to "overprint" the underlying darker mottled terrain. Scientists disagree about the chemical makeup of the dark materials, both sulfuric acid (common battery acid) and salty minerals, perhaps from a subsurface ocean, have been suggested. Analysis of images like this one may help to resolve this controversy. Surprisingly, either material could help to produce conditions below the surface that could be favorable to the formation of living organisms. The colored area is centered near the intersection of the equator and the Europan "prime meridian," where the longitude is assigned the value of 0 degrees. This is the sub-Jupiter point, where Jupiter always appears to be almost directly overhead. This phenomenon occurs because Europa takes the same period of time to rotate as it does to orbit around Jupiter (3.55 days). The area imaged in color is about 400 by 400 kilometers (250 by 250 miles), an area of about 160,000 square kilometers (about 62,000 square miles). The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is a division of the California Institute of Technology, Pasadena, CA. This image and other images and data received from Galileo are posted on the Galileo home page at http://galileo.jpl.nasa.gov . Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/images/io/ioimages.html . #####
Europa's Active Surface bw
A newly discovered impact cr
…
8/13/96
Date
8/13/96
Description
A newly discovered impact crater can be seen just right of the center of this image of Jupiter's moon Europa returned by NASA's Galileo spacecraft camera. The crater is about 30 kilometers (18.5 miles) in diameter. The impact excavated into Europa's icy crust, throwing debris (seen as whitish material) across the surrounding terrain. Also visible is a dark band, named Belus Linea, extending east-west across the image. This type of feature, which scientists call a "triple band," is characterized by a bright stripe down the middle. The outer margins of this and other triple bands are diffuse, suggesting that the dark material was put there as a result of possible geyser- like activity which shot gas and rocky debris from Europa's interior. The curving "X" pattern seen in the lower left corner of the image appears to represent fracturing of the icy crust and infilling by slush which froze in place. The crater is centered at about 2 degrees north latitude by 239 degrees west longitude. The image was taken from a distance of 156,000 kilometers (about 96,300 miles) on June 27, 1996, during Galileo's first orbit around Jupiter. The area shown is 860 by 700 kilometers (530 by 430 miles), or about the size of Oregon and Washington combined. The Galileo mission is managed by NASA's Jet Propulsion Laboratory.
Europa's Frozen Surface
PIA02590
Jupiter
Solid-State Imaging
Title
Europa's Frozen Surface
Original Caption Released with Image
Europa, a moon of Jupiter, appears as a thick crescent in this enhanced-color image from NASA's Galileo spacecraft, which has been orbiting Jupiter since 1995. The view combines images taken in violet, green and near-infrared filters in 1998 and 1995. The colors have been stretched to show the subtle differences in materials that cover the icy surface of Europa. Reddish linear features are some of the cracks and ridges, thousands of kilometers long, which are caused by the tides raised by the gravitational pull of Jupiter. Mottled, reddish "chaotic terrain" exists where the surface has been disrupted and ice blocks have moved around. The red material at the ridges and chaotic terrain is a non-ice contaminant and could be salts brought up from a possible ocean beneath Europa's frozen surface. Also visible are a few circular features, which are small impact craters. Europa's surface has very few craters, indicating that recent or current geologic activity has removed the traces of older impacts. The paucity of craters, coupled with other evidence, has led scientists to surmise that there could be an ocean of liquid water beneath Europa's surface. Where there is water, there could be life. This is why Europa is a target of current interest for study of the possibility of non-Earth life. A follow-up spacecraft to Galileo will be Europa Orbiter, which should determine whether or not Europa has an ocean. While at the University of Arizona, Tucson, Dr. Cynthia Phillips used this image in a detailed search for current geologic activity on Europa. Phillips is currently with the SETI Institute, Mountain View, Calif. For a study published in the Journal of Geophysical Research -- Planets last year, she compared the frames that make up this image with similar images taken in 1979 by the Voyager spacecraft and found no sign of changes due to geologic activity. That suggests a minimum surface age for Europa of about 30 million years, though the result does not rule out current geologic activity altogether, as the study was limited by the resolution of 2 kilometers (1.6 miles) or more per pixel in this image and the Voyager images. Future images by Europa Orbiter may allow a search for smaller-scale changes on Europa's surface. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Galileo and Voyager missions for NASA's Office of Space Science, Washington, D.C. Additional information about Galileo and its discoveries is available on the Galileo mission home page at http://galileo.jpl.nasa.gov [ http://galileo.jpl.nasa.gov ].
Close-up of Europa's Trailin
…
This complex terrain on Jupi
…
4/9/97
Date
4/9/97
Description
This complex terrain on Jupiter's moon, Europa, shows an area centered at 12 degrees north latitude, 274 degrees west longitude, in the trailing hemisphere. As Europa moves in its orbit around Jupiter, the trailing hemisphere is the portion which is always on the moon's backside opposite to its direction of motion. The area shown is about 100 kilometers by 140 kilometers (62 miles by 87 miles). The complex ridge crossing the picture in the upper left corner is part of a feature that can be traced hundreds of miles across the surface of Europa, extending beyond the edge of the picture. The upper right part of the picture shows terrain that has been disrupted by an unknown process, superficially resembling blocks of sea ice during a springtime thaw. Also visible are semicircular mounds surrounded by shallow depressions. These might represent the intrusion of material punching through the surface from below and partial melting of Europa's icy crust. The resolution of this image is about 180 meters (200 yards), this means that the smallest visible object is about a quarter of a mile across. This picture of Europa was taken by Galileo's Solid State Imaging system from a distance of 17,900 kilometers (11,100 miles) on the spacecraft's sixth orbit around Jupiter, on February 20, 1997. The Jet Propulsion Laboratory, Pasadena, CA, manages the mission for NASA's Office of Space Science, Washington D.C. This image and other images and data received from Galileo are posted on the World Wide Web Galileo mission home page at http://www.jpl.nasa.gov/galileo. #####
Europa
title
Europa
description
This image of Jupiter's icy moon Europa, the first Europa image returned by New Horizons, was taken with the spacecraft's Long Range Reconnaissance Imager (LORRI) camera at 07:19 Universal Time on February 27, from a range of 3.1 million kilometers (1.9 million miles). The longitude of the disk center is 307 degrees West and the image scale is 15 kilometers (9 miles) per pixel. This is one of a series of images designed to look for landforms near Europa's terminator -- the line dividing day and night -- where low Sun angles highlight subtle topographic features. Europa's fractured icy surface is thought to overlie an ocean about 100 kilometers (60 miles) below the surface, and the New Horizons team will be analyzing these images for clues about the nature of the icy crust and the forces that have deformed it. Europa is about the size of Earth's moon, with a diameter of 3,130 kilometers (1.945 miles). This is one of a handful of images of the Jupiter system already returned by New Horizons during its close approach to Jupiter. Most of the data being gathered by the spacecraft are stored onboard and will be downlinked to Earth during March and April 2007. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute
cryobot/hydrobot
This artist rendering shows
…
4/11/97
Date
4/11/97
Description
This artist rendering shows a proposed ice-penetrating cryobot and a submersible hydrobot that could be used to explore the ice-covered ocean on Jupiter's large satellite, Europa. Scientists propose first testing these instrument-ladened robots by sending them to Lake Vostok, a subglacial lake in Antarctica. The cryobot would melt its way through the ice cover and then deploy a hydrobot, a self-propelled underwater vehicle that would analyze the chemical composition of the ice and water in a search for signs of life. This proposed mission to Lake Vostok and Europa is being discussed by scientists and engineers at JPL, NASA, the National Science Foundation and universities and other agencies around the world.
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
Comparison of Ganymede and E
…
This image, taken by NASA's
…
12/16/00
Date
12/16/00
Description
This image, taken by NASA's Galileo spacecraft, shows a same-scale comparison between Arbela Sulcus on Jupiter's moon Ganymede (left) and an unnamed band on another Jovian moon, Europa (right). Arbela Sulcus is one of the smoothest lanes of bright terrain identified on Ganymede, and shows very subtle striations along its length. Arbela contrasts markedly from the surrounding heavily cratered dark terrain. On Europa, dark bands have formed by tectonic crustal spreading and renewal. Bands have sliced through and completely separated pre-existing features in the surrounding bright ridged plains. The scarcity of craters on Europa illustrates the relative youth of its surface compared to Ganymede's. Unusual for Ganymede, it is possible that Arbela Sulcus has formed by complete separation of Ganymede's icy crust, like bands on Europa. Prominent fractures on either side of Arbela appear to have been offset by about 65 kilometers (about 40 miles) along the length of the area of furrows and ridges, suggesting that strike-slip faulting was important in the formation of Arbela Sulcus. In the Ganymede image, north is to the upper left of the picture and the Sun illuminates the surface from the west. The image, centered at -14 degrees latitude and 347 degrees longitude, covers an area approximately 258 by 116 kilometers (160 by 72 miles.) The resolution is 133 meters (436 feet) per picture element. The images were taken on May 20, 2000, at a range of 13,100 kilometers (8,100 miles). In the Europa image, north is to the left of the picture and the Sun illuminates the surface from the east. The image, centered at -7 degrees latitude and 236 degrees longitude, covers an area approximately 275 by 424 kilometers (171 by 263 miles.) The resolution is 220 meters (about 720 feet) per picture element (re-sampled here to 133 meters, or 436 feet). The images were taken on Nov. 6, 1997, at a range of 21,500 kilometers (13,360 miles). The Jet Propulsion Laboratory, Pasadena, Calif., manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is a division of the California Institute of Technology in Pasadena. Images and data received from Galileo are posted on the Galileo mission home page at http://www.jpl.nasa.gov/galileo. Background information and educational context for the images can be found at http://www.jpl.nasa.gov/galileo/sepo . Images were produced by Brown University, Providence, R.I., http://www.planetary.brown.edu/, DLR (German Aerospace Center) Berlin, http://solarsystem.dlr.de , and University of Arizona, Tempe, http://www.lpl.arizona.edu/. # # # # #
Ganymede feature resembling
…
This frame compares a high-r
…
12/16/00
Date
12/16/00
Description
This frame compares a high-resolution view of Arbela Sulcus on Jupiter's moon Ganymede (top) with the gray band Thynia Linea on another Jovian moon, Europa (bottom), shown to the same scale. Both images are from NASA's Galileo spacecraft. Arbela Sulcus is one of the smoothest lanes of bright terrain identified on Ganymede, but subtle striations are apparent here along its length. This section of Arbela contrasts markedly from highly fractured terrain to its west and dark terrain to its east. On Europa, gray bands such as Thynia Linea have formed by tectonic crustal spreading and renewal. Such bands have sliced through and completely separated pre-existing features in the surrounding bright, ridged plains. The younger prominent double ridge Delphi Flexus cuts across Thynia Linea. The scarcity of craters on Europa attests to the relative youth of its surface compared to Ganymede's. Unusual for Ganymede, it is possible that Arbela Sulcus has formed by complete separation of Ganymede's icy crust, like bands on Europa. Tests of this idea come from detailed comparisons of their internal shapes and the relationships to the surrounding structures. In the Ganymede image, north is to the top of the picture and the Sun illuminates the surface from the west. The image, centered at -15 degrees latitude and 347 degrees longitude, covers an area approximately 34 by 26 kilometers (21 by 16 miles). The resolution is 34 meters (112 feet) per picture element. The image was taken on May 20, 2000, at a range of 3,370 kilometers (2,094 miles). In the Europa image, north is to the upper-right of the picture and the Sun illuminates the surface from the northwest. The image, centered at -66 degrees latitude and 161 degrees longitude, covers an area approximately 44 by 46 kilometers (27 by 29 miles). The resolution is 45 meters (147 feet) per picture element. The image was taken on September 26, 1998, at a range of 3,817 kilometers (2,371 miles). This image and other images and data received from Galileo are posted on the Galileo mission home page at http://www.jpl.nasa.gov/galileo . Background information and educational context for the images can be found at http://www.jpl.nasa.gov/galileo/sepo . The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Galileo mission for NASA's Office of Space Science, Washington, D.C. This image was produced by DLR (German Aerospace Center), Berlin, and Brown University, Providence, R.I., http://solarsystem.dlr.de/ and http://www.planetary.brown.edu/ . # # # # #
Regional Mosaic--Europa Chao
…
This mosaic of images taken
…
12/16/97
Date
12/16/97
Description
This mosaic of images taken by NASA's Galileo spacecraft camera shows a region of Jupiter's moon Europa that is characterized by dark and splotchy-looking terrain -- evidence of some of the most recent geologic activity on Europa. The mottled appearance results from chaotic areas where the bright, icy crust has broken apart to expose a darker material underneath. North is to the top of the image, and the Sun illuminates the scene from the right. The images were taken on Nov. 6. The smooth gray band at the lower part of image represents a zone where the Europan crust has been fractured, separated, and filled in with material from the interior. The chaotic terrain and the gray band show that Europa has been subjected to intense geological deformation. The mosaic is centered at 2.9 degrees south latitude and 234.1 degrees west longitude and covers an area of 261 kilometers by 168 kilometers (159 miles by 102 miles). The smallest distinguishable features in the image are about 229 meters (751 feet) across. These images were obtained on Nov. 6, 1997, when the Galileo spacecraft was approximately 21,700 kilometers (about 13,240 miles) from Europa. The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is a division of California Institute of Technology. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://www.jpl.nasa.gov/galileo. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo #####
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 ].
Galilean Moon Interiors
This artist's concept shows
…
6/4/98
Date
6/4/98
Description
This artist's concept shows cross-sections of the four largest moons of Jupiter, with the interior structures based on the latest information sent back by NASA's Galileo spacecraft. The moons depicted are (clockwise from bottom right) Callisto, Ganymede, Io and Europa. Scientists have modified their concept of Callisto's interior, based on the most recent Galileo findings. Whereas previously they believed that Callisto was completely undifferentiated, with a uniform mixture of rock and ice, scientists now say the interior has some separation of the ice and rock, but not nearly as much as the other three moons. Galileo data indicate that Ganymede is separated into a metallic core, rock mantle, and ice-rich outer shell, while Io has a metallic core and rock mantle, but no ice. Galileo data has also helped scientists refine their model of Europa's structure. They believe Europa has a metallic core surrounded by a rock mantle and a water ice-liquid outer shell. The core may be up to half the size of Europa's radius, with the water ice-liquid shell estimated to be between 80 to 170 kilometers thick (50 to 106 miles), with 100 kilometers (62 miles) considered the most likely thickness. Information on the interior structure of the four moons was obtained by studying radio Doppler data that is gathered when Galileo flies by the satellites. Each moon exerts a gravitational tug, but the tug's strength is determined by how much rock is contained within the moon (the higher the rock content, the stronger the tug). The tug changes the spacecraft's speed and the radio frequency of its signals. Scientists study those changes to determine the rock content and structure of the moon. This material was presented to the American Astronomical Society meeting in San Diego, CA on June 4, 1998. The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is a division of California Institute of Technology (Caltech). This image, along with other images and data received from Galileo, is available on the Galileo mission home page at http://www.jpl.nasa.gov/galileo. Background information and educational context for the images can be found at http://www.jpl.nasa.gov/galileo/sepo . #####
This image of Europa, an icy
…
1/17/97
Date
1/17/97
Description
This image of Europa, an icy satellite of Jupiter, was obtained from a range of 39028 miles (62089 kilometers) by the Galileo spacecraft during its fourth orbit around Jupiter and its first close pass of Europa. The image spans an area 78 miles by 244 miles (126 km by 393 km), and shows features as small as a mile (1.6 km) across. Sun illumination is from the right, revealing several ridges crossing the scene, plateaus commonly several miles (10 km) across, and patches of smooth, low-lying darker materials. No prominent impact craters are visible, indicating the surface in this location is not geologically ancient. Some ridges have gaps, and subtle textural differences in these areas indicate that missing ridge segments probably were swept away by volcanic flows. The flow deposits are probably composed mainly of water ice, the chief constituent of the surface of Europa. The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://www.jpl.nasa.gov/galileo. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo #####
Europa Ridges, Hills and Dom
…
This moderate-resolution vie
…
4/9/97
Date
4/9/97
Description
This moderate-resolution view of the surface of one of Jupiter's moons, Europa, shows the complex icy crust that has been extensively modified by fracturing and the formation of ridges. The ridge systems superficially resemble highway networks with overpasses, interchanges and junctions. From the relative position of the overlaps, it is possible to determine the age sequence for the ridge sets. For example, while the 8-kilometer- wide (5-mile) ridge set in the lower left corner is younger than most of the terrain seen in this picture, a narrow band cuts across the set toward the bottom of the picture, indicating that the band formed later. In turn, this band is cut by the narrow 2-kilometer-wide (1.2-mile) double ridge running from the lower right to upper left corner of the picture. Also visible are numerous clusters of hills and low domes as large as 9 kilometers (5.5 miles) across, many with associated dark patches of non-ice material. The ridges, hills and domes are considered to be ice-rich material derived from the subsurface. These are some of the youngest features seen on the surface of Europa and could represent geologically young eruptions. This area covers about 140 kilometers by 130 kilometers (87 miles by 81 miles) and is centered at 12.3 degrees north latitude, 268 degrees west longitude. Illumination is from the east (right side of picture). The resolution is about 180 meters (200 yards) per pixel, meaning that the smallest feature visible is about a city block in size. The picture was taken by the Solid State Imaging system on board the Galileo spacecraft on February 20, 1997, from a distance of 17,700 kilometers (11,000 miles) during its sixth orbit around Jupiter. The Jet Propulsion Laboratory, Pasadena, CA, manages the mission for NASA's Office of Space Science, Washington D.C. This image and other images and data received from Galileo are posted on the World Wide Web Galileo mission home page at http://www.jpl.nasa.gov/galileo. #####
Europa
PIA09246
Jupiter
LORRI
Title
Europa
Original Caption Released with Image
This image of Jupiter's icy moon Europa, the first Europa image returned by New Horizons, was taken with the spacecraft's Long Range Reconnaissance Imager (LORRI) camera at 07:19 Universal Time on February 27, from a range of 3.1 million kilometers (1.9 million miles). The longitude of the disk center is 307 degrees West and the image scale is 15 kilometers (9 miles) per pixel. This is one of a series of images designed to look for landforms near Europa's terminator -- the line dividing day and night -- where low Sun angles highlight subtle topographic features. Europa's fractured icy surface is thought to overlie an ocean about 100 kilometers (60 miles) below the surface, and the New Horizons team will be analyzing these images for clues about the nature of the icy crust and the forces that have deformed it. Europa is about the size of Earth's moon, with a diameter of 3,130 kilometers (1.945 miles). This is one of a handful of images of the Jupiter system already returned by New Horizons during its close approach to Jupiter. Most of the data being gathered by the spacecraft are stored onboard and will be downlinked to Earth during March and April 2007.
High-Resolution Europa Mosai
…
This mosaic of images from N
…
12/16/97
Date
12/16/97
Description
This mosaic of images from NASA's Galileo spacecraft camera shows some of the highest resolution images of Jupiter's moon Europa ever acquired. The hundreds of ridges that cut across each other indicate multiple episodes of ridge formation either by volcanic or tectonic activity within the ice. The images were taken on Nov. 6, 1997 from a range of about 3,250 kilometers (about 1,990 miles). North is to the top of the image and the Sun illuminates the scene from the left. Also visible in the image are numerous isolated mountains or "massifs". The highest of these, located in the upper right corner and lower center of the mosaic, are approximately 500 meters (1,640 feet) high. Irregularly shaped areas where the ice surface appears to be lower than the surrounding plains (in the left-center and lower left corner of the mosaic) may be related to the chaotic areas of iceberg-like features seen in earlier Galileo images of Europa. The mosaic, centered at 35.4 degrees north latitude and 86.8 degrees west longitude, covers an area of 66 by 55 kilometers (108 by 90 miles). The smallest distinguishable features in the image are about 68 meters (223 feet) across. The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is a division of California Institute of Technology. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://www.jpl.nasa.gov/galileo. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo #####
Europa--Ice Rafting
A small region of the thin,
…
12/16/97
Date
12/16/97
Description
A small region of the thin, disrupted ice crust in the Conamara region of Jupiter's moon Europa shows the interplay of surface color with ice structures in this image produced with data from NASA's Galileo spacecraft camera. The white and blue colors outline areas that have been blanketed by a fine dust of ice particles ejected when an explosive impact created the large crater Pwyll (26 kilometers or 16 miles in diameter) located some 1,000 kilometers (about 620 miles) to the south. Also visible are a few small craters of less than 500 meters or 547 yards in diameter that were probably formed at the same when the impact likely threw out large, intact, blocks of around the area. The unblanketed surface has a reddish brown color that has been painted by mineral contaminants carried and spread by water vapor released from below the crust when it was disrupted. The original color of the icy surface was probably a deep blue seen in large areas elsewhere on Europa's surface. The colors in this picture have been enhanced for visibility. North is to the top of the picture and the Sun illuminates the surface from the right. The image, centered at 9 degrees latitude and 86.5 degrees south longitude, covers an area approximately 70 by 30 kilometers (44 by 19 miles), and combines data taken by the Galileo Solid State Imaging (CCD) system during three of the spacecraft's orbits through the Jovian system. Low- resolution color (violet, green, and infrared) data acquired in September 1996 were combined with medium-resolution images from December 1996 to produce synthetic color images. These were then combined with a high-resolution mosaic of images acquired on Feb. 20, 1997 at a resolution of 54 meters (59 yards) per picture element and at a range of 5,340 kilometers (3,320 miles). The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is a division of California Institute of Technology. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://www.jpl.nasa.gov/galileo. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo #####
Europa and Callisto under th
…
PIA02861
Sol (our sun)
Imaging Science Subsystem
Title
Europa and Callisto under the watchful gaze of Jupiter
Original Caption Released with Image
One moment in an ancient, orbital dance is caught in this color picture taken by NASA's Cassini spacecraft on Dec. 7, 2000, just as two of Jupiter's four major moons, Europa and Callisto, were nearly perfectly aligned with each other and the center of the planet. The distances are deceiving. Europa, seen against Jupiter, is 600,000 kilometers (370,000 miles) above the planet's cloud tops. Callisto, at lower left, is nearly three times that distance from the cloud tops. Europa is a bit smaller than Earth's Moon and has one of the brightest surfaces in the solar system. Callisto is 50 percent bigger -- roughly the size of Saturn's largest satellite, Titan -- and three times darker than Europa. Its brightness had to be enhanced in this picture, relative Europa's and Jupiter's, in order for Callisto to be seen in this image. Europa and Callisto have had very different geologic histories but share some surprising similarities, such as surfaces rich in ice. Callisto has apparently not undergone major internal compositional stratification, but Europa's interior has differentiated into a rocky core and an outer layer of nearly pure ice. Callisto's ancient surface is completely covered by large impact craters: The brightest features seen on Callisto in this image were discovered by the Voyager spacecraft in 1979 to be bright craters, like those on our Moon. In contrast, Europa's young surface is covered by a wild tapestry of ridges, chaotic terrain and only a handful of large craters. Recent data from the magnetometer carried by the Galileo spacecraft, which has been in orbit around Jupiter since 1995, indicate the presence of conducting fluid, most likely salty water, inside both worlds. Scientists are eager to discover whether the surface of Saturn's Titan resembles that of Callisto or Europa, or whether it is entirely different when Cassini finally reaches its destination in 2004. Cassini 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 Cassini mission for NASA's Office of Space Science, Washington, D.C.
Close-up of Europa's Surface
This close-up view of the ic
…
4/11/97
Date
4/11/97
Description
This close-up view of the icy surface of Europa, a moon of Jupiter, was obtained on December 20, 1996, by the Solid State Imaging system on board the Galileo spacecraft during its fourth orbit around Jupiter. The view is about 13 kilometers by 18 kilometers (8 miles by 11 miles) and has a resolution of 26 meters (28 yards). The Sun illuminates the scene from the east (right). A flat smooth area about 3.2 kilometers (2 miles) across is seen in the left part of the picture. This area resulted from flooding by a fluid which erupted onto the surface and buried sets of ridges and grooves. The smooth area contrasts with a distinctly rugged patch of terrain farther east, to the right of the prominent ridge system running down the middle of the picture. The rugged patch of terrain is 4 kilometers (2.5 miles) across and represents localized disruption of the complex network of ridges in the area. Eruptions of material onto the surface, crustal disruption, and the formation of complex networks of folded and faulted ridges show that significant energy was available in the interior of Europa. Although small impact craters are most easily seen in the smooth area, they occur throughout the ridged terrain seen in this view. The Jet Propulsion Laboratory, Pasadena, CA, manages the mission for NASA's Office of Space Science, Washington D.C. This image and other images and data received from Galileo are posted on the World Wide Web Galileo mission home page at: http://www.jpl.nasa.gov/galileo. #####
Europa Impact
title
Europa Impact
date
04.04.1997
description
This feature on Jupiter's moon Europa was seen as a dark, diffuse circular patch on a previous Galileo global image of Europa's leading hemisphere. The bulls-eye pattern appears to be a 140-kilometer-wide impact scar (about the size of the island of Hawai'i) that formed as the surface fractured minutes after a mountain-sized asteroid or comet slammed into the satellite. This approximately 214-kilometer-wide picture is the product of three images that have been processed in false color to enhance shapes and compositions. North is toward the top of this picture, which is illuminated from sunlight coming from the west. This color composite reveals a sequence of events, that have modified the surface of Europa. The earliest event was the impact that formed the Tyre structure at 340N latitude and 146.50W longitude. This impact was followed by the formation of the reddish lines superposed on Tyre. The red color designates areas that are probably a dirty water-ice mixture. The fine blue-green lines crossing the region from west to east appear to be ridges that formed after the crater. The images were taken on April 4, 1997, at a resolution of 595 meters per picture element and a range of 29,000 kilometers. The images were taken by the Galileo spacecraft's Solid-State Imaging System. *Image Credit*: University of Arizona
Europa Astrobiology Lander
title
Europa Astrobiology Lander
description
This Flagship class mission would build on the findings of the Europa Explorer Mission, and would perform astrobiology related exploration on the surface of Europa.
This image of Jupiter's sate
…
1/17/97
Date
1/17/97
Description
This image of Jupiter's satellite Europa was obtained from a range of 7364 miles (11851 km) by the Galileo spacecraft during its fourth orbit around Jupiter and its first close pass of Europa. The image spans 30 miles by 57 miles (48 km x 91 km) and shows features as small as 800 feet (240 meters) across, a resolution more than 150 times better than the best Voyager coverage of this area. The sun illuminates the scene from the right. The large circular feature in the upper left of the image could be the scar of a large meteorite impact. Clusters of small craters seen in the right of the image may mark sites where debris thrown from this impact fell back to the surface. Prominent doublet ridges over a mile (1.6 km) wide cross the plains in the right part of the image, younger ridges overlap older ones, allowing the sequence of formation to be determined. Gaps in ridges indicate areas where emplacement of new surface material has obliterated pre-existing terrain. The Jet Propulsion Laboratory, Pasadena, CA manages the mission for NASA's Office of Space Science, Washington, DC. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://www.jpl.nasa.gov/galileo. Background information and educational context for the images can be found at URL http://www.jpl.nasa.gov/galileo/sepo #####
Cresent Europa
Title
Cresent Europa
Full Description
This mosaic of Europa, the smallest Galilean satellite, was taken by Voyager 2. This face of Europa is centered at about the 300 degree meridian. The bright areas are probably ice deposits, whereas the darkened areas may be the rocky surface or areas with a more patchy distribution of ice. The most unusual features are the systems of long linear structures that cross the surface in various directions. Some of these linear structures are over 1,000 kilometers long and about 2 or 3 kilometers wide. They may be fractures or faults which have disrupted the surface.
Date
09/12/1996
NASA Center
Jet Propulsion Laboratory
Dark Bands on Europa
Dark crisscrossing bands on
…
8/13/96
Date
8/13/96
Description
Dark crisscrossing bands on Jupiter's moon Europa represent widespread disruption from fracturing and the possible eruption of gases and rocky material from the moon's interior in this four-frame mosaic of images from NASA's Galileo spacecraft. These and other features suggest that soft ice or liquid water was present below the ice crust at the time of disruption. The data do not rule out the possibility that such conditions exist on Europa today. The pictures were taken from a distance of 156,000 kilometers (about 96,300 miles) on June 27, 1996. Many of the dark bands are more than 1,600 kilometers (1,000 miles) long, exceeding the length of the San Andreas fault of California. Some of the features seen on the mosaic resulted from meteoritic impact, including a 30-kilometer (18.5 mile) diameter crater visible as a bright scar in the lower third of the picture. In addition, dozens of shallow craters seen in some terrains along the sunset terminator zone (upper right shadowed area of the image) are probably impact craters. Other areas along the terminator lack craters, indicating relatively youthful surfaces, suggestive of recent eruptions of icy slush from the interior. The lower quarter of the mosaic includes highly fractured terrain where the icy crust has been broken into slabs as large as 30 kilometers (18.5 miles) across. The mosaic covers a large part of the northern hemisphere and includes the north pole at the top of the image. The sun illuminates the surface from the left. The area shown is centered on 20 degrees north latitude and 220 degrees west longitude and is about as wide as the United States west of the Mississippi River. The Galileo mission is managed by NASA's Jet Propulsion Laboratory.
Europa During Voyager 2 Clos
…
PIA00459
Jupiter
Imaging Science Subsystem -
…
Title
Europa During Voyager 2 Closest Approach
Original Caption Released with Image
This color image of the Jovian moon Europa was acquired by Voyager 2 during its close encounter on Monday morning, July 9. Europa, the size of our moon, is thought to have a crust of ice perhaps 100 kilometers thick which overlies the silicate crust. The complex array of streaks indicate that the crust has been fractured and filled by materials from the interior. The lack of relief, any visible mountains or craters, on its bright limb is consistent with a thick ice crust. In contrast to its icy neighbors, Ganymede and Callisto, Europa has very few impact craters. One possible candidate is the small feature near the center of this image with radiating rays and a bright circular interior. The relative absence of features and low topography suggests the crust is young and warm a few kilometers below the surface. The tidal heating process suggested for Io also may be heating Europa's interior at a lower rate.
Gibbous Europa
Title
Gibbous Europa
Explanation
Although the phase [ http://antwrp.gsfc.nasa.gov/apod/ap010218.html ] of this moon might appear familiar, the moon itself might not. In fact, this gibbous phase [ http://en.wikipedia.org/wiki/Gibbous ] shows part of Jupiter [ http://www.nineplanets.org/jupiter.html ]'s moon Europa [ http://www.nineplanets.org/europa.html ]. The robot spacecraft Galileo [ http://en.wikipedia.org/wiki/ Galileo_%28spacecraft%29 ] captured this image [ http://planetimages.blogspot.com/2005/09/ new-color-views-of-europa.html ] mosaic during its mission orbiting Jupiter from 1995 - 2003. Visible are plains [ http://antwrp.gsfc.nasa.gov/apod/ap981215.html ] of bright ice [ http://antwrp.gsfc.nasa.gov/apod/ap000418.html ], cracks [ http://antwrp.gsfc.nasa.gov/apod/ap980310.html ] that run to the horizon, and dark patches [ http://antwrp.gsfc.nasa.gov/apod/ap970815.html ] that likely contain both ice and dirt. Raised terrain [ http://antwrp.gsfc.nasa.gov/apod/ap980303.html ] is particularly apparent near the terminator [ http://en.wikipedia.org/wiki/ Terminator_%28solar%29 ], where it casts shadows [ http://antwrp.gsfc.nasa.gov/apod/ap001225.html ]. Europa [ http://antwrp.gsfc.nasa.gov/apod/ap961120.html ] is nearly the same size as Earth's Moon [ http://antwrp.gsfc.nasa.gov/apod/ap020127.html ], but much smoother, showing few highlands [ http://csep10.phys.utk.edu/astr161/lect/moon/ moon_surface.html ] or large impact craters [ http://antwrp.gsfc.nasa.gov/apod/ap010809.html ]. Evidence and images from the Galileo spacecraft [ http://solarsystem.nasa.gov/galileo/ ], indicated that liquid oceans might exist [ http://antwrp.gsfc.nasa.gov/apod/ap980102.html ] below the icy surface. To test speculation that these seas hold life, ESA [ http://en.wikipedia.org/wiki/European_Space_Agency ] has started preliminary development of the Jovian Europa Orbiter [ http://www.jpl.nasa.gov/europaorbiter/europao.htm ], a spacecraft proposed to orbit Europa. If the surface ice is thin enough, a future mission might drop hydrobots [ http://www.jpl.nasa.gov/galileo/mission/ journey-future.html ] to burrow into the oceans and search for life.
Europa's Synthetic Subsurfac
…
Title
Europa's Synthetic Subsurface Heat Transport (Version 1)
Abstract
Under Europa's icy surface are vast extraterrestrial oceans. This conceptual animation depicts simulated heat transport of these subsurface oceans. Please note that the simulated heat transport in this animation is only conceptual and a more accurate representation can be found at animation #2946.
Completed
2004-05-04
Other Worlds and HD 38529
Title
Other Worlds and HD 38529
Explanation
After the latest round of discovery announcements [ http://www.iau.org/ga24press/ ], the list of known worlds of distant suns [ http://www.spaceart.org/lcook/extrasol.html ] has grown to 50 [ http://www.spaceref.com/news/viewnews.html?id=200 ]. While extrasolar planet [ http://exoplanets.org/ ] discoveries are [ http://obswww.unige.ch/~udry/planet/planet.html ] sure to continue, none - so far [ http://sim.jpl.nasa.gov/ ] - points clearly to another planetary system like our own [ http://antwrp.gsfc.nasa.gov/apod/ap991229.html ]. Take, for example, the newly discovered parent [ http://antwrp.gsfc.nasa.gov/apod/ap990611.html ] star HD38529 [ http://www.obspm.fr/encycl/HD38529.html ]. Shining in Earth's night sky at 6th magnitude, this sun-like star lies 137 light-years away in the constellation Orion [ http://aibn47.astro.uni-bonn.de/~gallery/constellations/orion/ main.html ]. Like most of the known extrasolar planets [ http://www.obspm.fr/encycl/encycl.html ], HD38529's planet was discovered by detecting the telltale Doppler wobble [ http://exoplanets.org/doppler.html ] in the parent star's spectrum. The data reveal that this planet orbits once every 14.3 days at an average of only 0.13 times the Earth-Sun distance and has a minimum of 0.77 Jupiter masses (about 240 Earth masses). There is even evidence [ http://www.iau.org/ga24press/pr000807_3.html#1 ] in the wobble data that HD38529, and other stars with one known planet have additional massive planets orbiting them. In this dramatic artist's vision, HD38529 and its newfound world are viewed from the moon of another massive ringed planet [ http://antwrp.gsfc.nasa.gov/apod/ap000330.html ] orbiting farther out. The ringed planet's moon is imagined to have a thin atmosphere and a surface covered with icy sheets and ridges similar to those found on Jupiter's moon Europa [ http://galileo.jpl.nasa.gov/moons/europa.html ].
Jupiter's Inner Satellites a
…
Title
Jupiter's Inner Satellites and Ring Components
Description
This schematic cut-away view of the components of Jupiter's ring system shows the geometry of the rings in relation to Jupiter and to the small inner satellites, which are the source of the dust which forms the rings. [figure removed for brevity, see original site] *The Formation of Jupiter's Ring System* The innermost and thickest ring, shown in gray shading, is the halo that ends at the main ring. The thin, narrow main ring, shown with red shading, is bounded by the 16- kilometer-wide (10-miles) satellite Adrastea and shows a marked decrease in brightness near the orbit of Jupiter's innermost moon, Metis. It is composed of fine particles knocked off Adrastea and Metis. Although the orbits of Adrastea and Metis are about 1,000 kilometers (about 600 miles) apart, that separation is not depicted in this drawing. Impacts by small meteoroids (fragments of asteroids and comets) into these small, low-gravity satellites feed material into the rings. Thebe and Amalthea, the next two satellites in increasing distance from Jupiter, supply dust which forms the thicker, disk-like "gossamer" rings. The gossamer rings, depicted with yellow and green shading, are thicker because the source satellites orbit Jupiter on inclined paths [figure removed for brevity, see original site] *Satellite Interactions with Jupiter's Ring System* These small satellites all orbit closer to Jupiter than the four largest Galilean satellites, Io, Europa, Ganymede and Callisto, which were discovered nearly 400 years ago. The orbital distances of the moons are drawn relative to the size of Jupiter.*Jupiter's Main Ring and Inner Satellites*Side view of system:Overhead view of system: [figure removed for brevity, see original site] [figure removed for brevity, see original site] The Jupiter image was created from a map based on data obtained by the Hubble Space Telescope. JPL manages the Galileo mission for NASA's Office of Space Science, Washington, DC. The images are posted on the Internet athttp://photojournal.jpl.nasa.gov/ [ http://photojournal.jpl.nasa.gov/ ]and athttp://galileo.jpl.nasa.gov [ http://galileo.jpl.nasa.gov ]. Background information and educational context for the images can be found at:http://www.jpl.nasa.gov/galileo/sepo [ http://www.jpl.nasa.gov/galileo/sepo ].
Date
09.15.1998
Terrestrial Planet Interiors
title
Terrestrial Planet Interiors
description
*Mercury* Mercury has an average density of 5430 kilograms per cubic meter, which is second only to Earth among all the planets. It is estimated that the planet Mercury, like Earth, has a ferrous core with a size equivalent to two-thirds to three-fourths that of the planet's overall radius. The core is believed to be composed of an iron-nickel alloy covered by a mantle and surface crust. *Venus* It is believed that the composition of the planet Venus is similar to that of Earth. The planet crust extends to around 10-30 kilometers below the surface, under which the mantle reaches to a depth of some 3000 kilometers. The planet core comprises a liquid iron-nickel alloy. Average planet density is 5240 kilograms per cubic meter. *Earth* The Earth comprises three separate layers: a crust, a mantle, and a core (in descending order from the surface). The crust thickness averages 30 kilometers for land masses and 5 kilometers for seabeds. The mantle extends from just below the crust to some 2900 kilometers deep. The core below the mantle begins at a depth of around 5100 kilometers, and comprises an outer core (liquid iron-nickel alloy) and inner core (solid iron-nickel alloy). The crust is composed mainly of granite in the case of land masses and basalt in the case of seabeds. The mantle is composed primarily of peridotite and high-pressure minerals. Average planet density is 5520 kilograms per cubic meter. *Mars* Mars is roughly one-half the diameter of Earth. Due to its small size, it is believed that the martian center has cooled. Geological structure is mainly rock and metal. The mantle below the crust comprises iron-oxide-rich silicate. The core is made up of an iron-nickel alloy and iron sulfide. Average planet density is 3930 kilograms per cubic meter. *Pluto* The structure of Pluto is not very well understood at present. Nevertheless, spectroscopic observation from Earth in the 1970s has revealed that the planet surface is covered with methane ice. Surface temperature is -230?C (-382?F), and the frozen methane exhibits a bright coloration. However, with the exception of the polar caps, the frozen methane surface is seen to change to a dark red when eclipsed by its moon Charon. Average planet density is 2060 kilograms per cubic meter. The low average density requires that the planet must be a mix of ice and rock. *Image Credit*: Lunar and Planetary Institute
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