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A New Hot Spot on Northern I …
PIA03602
Jupiter
Near Infrared Mapping Spectr …
Title A New Hot Spot on Northern Io
Original Caption Released with Image NASA's Galileo spacecraft has returned infrared imagery of a new hot spot on Jupiter's moon Io that was the source of a towering plume in August 2001, indicating a sulfur-dioxide concentration that may have been fallout from the plume. Galileo's near-infrared mapping spectrometer captured the image on the left during an Oct. 16, 2001 flyby of Io. Coloring indicates the intensity of glowing at a wavelength of 4.1 microns. Yellow, red, and white represent high temperatures. Black is where the near-infrared glow was so intense the image was saturated. Greens and blues are cold. The visible-light image on the right was obtained by Galileo's camera in 1999, before any volcanic activity was seen at this site. The first sign of activity came in August 2001, when Galileo detected an infrared hot spot and the tallest volcanic plume ever seen at Io. The dark blue band north of the hot spot in the new infrared image represents a concentration of sulfur-dioxide, which has a strong signature in the infrared. The sulfur-dioxide is thought to be from the fallout of the plume. The image shows high temperatures corresponding to yellow flows in the center of the visible-light image, and from a small caldera at the 8 o'lock position. 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. 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 ]. Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/gallery/io.cfm [ http://galileo.jpl.nasa.gov/gallery/io.cfm ].
Io's Tupan Caldera in Infrar …
PIA03601
Jupiter
Near Infrared Mapping Spectr …
Title Io's Tupan Caldera in Infrared
Original Caption Released with Image Tupan Caldera, a volcanic crater on Jupiter's moon Io, has a relatively cool area, possibly an island, in its center, as indicated by infrared imagery from NASA's Galileo spacecraft. A thermal portrait of Tupan collected by the near-infrared mapping instrument on Galileo during an Oct. 16, 2001 flyby is presented on the right, beside a visible-light image from Galileo's camera for geographical context. The infrared image uses false color to indicate intensity of glowing at a wavelength of 4.7 microns. Reds and yellows indicate hotter regions, blues are cold. The hottest areas correspond to the dark portions in the visible-light image and are probably hot lavas. The central region in the crater may be an island or a topographically high region. Parts of it are cold enough for sulfur-dioxide to condense. Tupan, an active volcano on Io since at least 1996, was named for the Brazilian native god of thunder. 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. 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 ]. Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/gallery/io.cfm [ http://galileo.jpl.nasa.gov/gallery/io.cfm ].
Amirani Lava Flow on Io
PIA03533
Jupiter
Near Infrared Mapping Spectr …
Title Amirani Lava Flow on Io
Original Caption Released with Image The Amirani lava flow on Jupiter's moon Io appears to be made up of many individual flows, the newest flows are the brightest spots in this infrared image from NASA's Galileo spacecraft. The thermal map from Galileo's near-infrared mapping spectrometer instrument is presented on the left, beside a reference picture of the same area from Galileo's camera. The infrared image uses false color to indicate intensity of glowing at a wavelength of 5 microns. White, reds and yellows indicate hotter regions, blues are cold. North is to the top. Amirani is the largest active lava flow known in the solar system. Galileo has previously observed many changes in its flows [ http://photojournal.jpl.nasa.gov/catalog/PIA02585 ]. In this infrared image, Amirani includes the two brightest spots and two others closest to that pair. The image also shows three other active volcanoes on Io: Maui (lower left, corresponding to a dark, roughly circular area in the reference image), Dusurra (top, corresponding to the dark, roughly circular area at the top of the reference image) and an unnamed hot spot that appears as an elongated small feature in the reference image between Dussura and the Amirani flow. Of Amirani's four bright areas, the one on the lower left corresponds to what is thought to be the flow's vent: a dark elongated crater surrounded by red materials. Red deposits are indicative of recent plume activity on Io. The other three bright areas along the flow correspond to where hot lavas are breaking out. Notice that the dark flow going from the main flow to the left is not seen in the infrared image. This indicates that this flow has cooled and is no longer active. NASA's Voyager spacecraft detected a plume more than 20 years ago from a location near the end of this now-inactive flow. The plume was probably created by interaction of the hot flow with sulfur-dioxide frost, in the same way as Io's Prometheus plume [ http://photojournal.jpl.nasa.gov/catalog/PIA02512 ]. Once the flow cooled, the plume shut off. This infrared image was taken on Aug. 6, 2001. It has a resolution of about 9 kilometers (6 miles) per picture element. 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. 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 ] .
Io in Infrared with Giant Pl …
PIA03534
Jupiter
Near Infrared Mapping Spectr …
Title Io in Infrared with Giant Plume's New Hot Spot
Original Caption Released with Image Nine previously unknown volcanoes have been discovered from this infrared image of Jupiter's moon Io, acquired by NASA's Galileo spacecraft on Oct. 16, 2001. The infrared image, on the right, serves as a thermal map to a section of Io's surface from pole to pole. An image from Galileo's camera showing the same face of Io (left) is included for correlating the heat-sensing infrared data with geological features apparent in visible wavelengths. The infrared image uses false color to portray the intensity with which the surface glows at the invisible wavelength of 5 microns, as observed by Galileo's near infrared mapping spectrometer instrument. White, reds and yellows indicate hotter regions, blues are cold. The resolution varies from 24 to 39 kilometers (15 to 24 miles) per picture element. Some of the hot spots visible in this image were not seen in a similar infrared image taken just 10 weeks earlier [ http://photojournal.jpl.nasa.gov/catalog/PIA02591 ] of an overlapping section of Io. Three sites of major activity in the images are Prometheus, which is a bright spot at center left, Amirani, which is an elongated feature in the upper right, and the site where a giant plume was erupting in August, which is the bright spot near the top of the image. 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. 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 ] .
Io in Infrared, Night and Da …
PIA03535
Jupiter
Near Infrared Mapping Spectr …
Title Io in Infrared, Night and Day
Original Caption Released with Image Hot eruption sites scattered across Jupiter's moon Io stand out dramatically in an infrared image taken Oct. 13, 2001, by NASA's Galileo spacecraft as it sped past this most volcanically active of all known worlds. The infrared image (right) serves as a thermal map to nearly a full hemisphere of Io. An image from Galileo's camera showing the same face of Io (left) is included for correlating the heat-sensing infrared data with geological features apparent in visible wavelengths. When Galileo snapped the infrared shot, the left half of the hemisphere was actually in darkness and the right half in daylight. The infrared image uses false color to portray the intensity with which the surface glows at the invisible wavelength of 5 microns, as observed by Galileo's near infrared mapping spectrometer instrument. White, reds and yellows indicate hotter regions, blues are cold. The resolution varies from 83 to 93 kilometers (52 to 58 miles) per picture element. Four previously unknown volcanoes have been discovered from this image, including one also detected in another infrared image taken the same day. Those new-found hot spots are faint. Among the more easily identified brighter volcanoes in the image are the pair Pillan and Pele located near the left-hand edge at about 8 o'clock if the circular image is taken as a clock face. Marduk is located a little farther from the edge at 7 o'clock. The bright spot at about 2 o'clock is the site where a plume was seen erupting about 500 kilometers (320 miles) high 10 weeks before this image was taken. 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. 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 ] .
Ammonia Ice near Jupiter's G …
PIA02569
Sol (our sun)
Near Infrared Mapping Spectr …
Title Ammonia Ice near Jupiter's Great Red Spot
Original Caption Released with Image The first discrete ammonia ice cloud positively identified on Jupiter is shown in this image taken by NASA's Galileo spacecraft. Ammonia ice (light blue) is shown in clouds to the northwest (upper left) of the Great Red Spot (large red spot in middle of figure). This unusual cloud, inside the turbulent wake region near the Great Red Spot, is produced by powerful updrafts of ammonia-laden air from deep within Jupiter's atmosphere. These updrafts are generated by the turbulence induced in Jupiter's massive westward-moving air currents by the nearby Great Red Spot. This false-color image was composed from several near-infrared color images obtained by the Galileo's near-infrared mapping spectrometer on June 26, 1996. Reddish-orange areas show high-level clouds, yellow areas depict mid-level clouds, and green areas depict lower-level clouds. Darker areas are cloud-free regions. Light blue depicts regions of middle-to-high-altitude-level ammonia ice clouds. The Great Red Spot, which has existed for at least 300 years, is the oldest and largest weather system in our solar system. It measures over 20,000 kilometers wide (over 12,400 miles), which is about twice as wide as Earth. The Jet Propulsion Laboratory, Pasadena, Calif., manages the mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at http://galileo.jpl.nasa.gov [ http://galileo.jpl.nasa.gov ]. Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/gallery/io.cfm [ http://galileo.jpl.nasa.gov/gallery/io.cfm ].
Temperature Map of Pele, Io
PIA02560
Jupiter
Near Infrared Mapping Spectr …
Title Temperature Map of Pele, Io
Original Caption Released with Image Pele, one of Io's best-known volcanoes, was observed by the infrared spectrometer, an instrument onboard NASA's Galileo spacecraft, during the flyby of Jupiter's moon Io on February 22, 2000. The temperature map is shown here on the left in false color, superimposed on a visible color image of the Pele region obtained by the Voyager spacecraft in 1979. The red color represents the hottest lava flows. The purple colors are cooler materials. Preliminary results show that the temperatures of the hottest lava flows are at least 1,400 Kelvin (about 2,000 Fahrenheit), consistent with the temperatures of basaltic lava seen on the Kilauea volcano in Hawaii. It is possible that the eruption temperatures at Pele are even higher, as lava cools quickly once it starts to spread over the surface. The Voyager context image is 200 kilometers (124 miles) across. The Jet Propulsion Laboratory, Pasadena, Calif., manages the mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page athttp://galileo.jpl.nasa.gov [ http://galileo.jpl.nasa.gov ]. Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/gallery/io.cfm [ http://galileo.jpl.nasa.gov/gallery/io.cfm ].
Myriad of Hot Spots on Io
PIA02558
Jupiter
Near Infrared Mapping Spectr …
Title Myriad of Hot Spots on Io
Original Caption Released with Image Changes in the volcanoes on Jupiter's moon Io can be seen in these three views, taken by NASA's Galileo spacecraft during its three flybys of Io in October 1999, November 1999 and February 2000. All the images show the active volcanoes as bright yellow, corresponding to hot lava flows that appear glowing in infrared wavelengths. The three views were taken by the spacecraft's near-infrared mapping spectrometer instrument and show the comparison of a typical low-resolution observation to the high-resolution views. The regional observations taken during the recent Io flybys are superimposed on an image taken during Galileo in 1996. The Prometheus volcano is seen near the middle of all three images. Before the recent flybys, only Prometheus and three other volcanoes were known to be active in this region. After these and other high-resolution observations, scientists were able to detect 14 volcanoes in the same area. The fainter volcanoes (hot spots) show some significant changes over intervals of 1 to 3 months. The area shown by all three observations put together is about 2 million square kilometers (about 770,000 square miles) and covers about 5 percent of Io's surface. The Jet Propulsion Laboratory, Pasadena, Calif., manages the mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page athttp://galileo.jpl.nasa.gov [ http://galileo.jpl.nasa.gov ]. Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/gallery/io.cfm [ http://galileo.jpl.nasa.gov/gallery/io.cfm ].
Europa Impact Crater
PIA02561
Jupiter
Near Infrared Mapping Spectr …
Title Europa Impact Crater
Original Caption Released with Image A newly discovered, city-sized impact crater viewed by NASA's Galileo spacecraft may shed new light on the nature of the enigmatic icy surface of Jupiter's moon Europa. This false-color image reveals the scar of a past major impact of a comet or small asteroid on Europa's surface. The bright, circular feature at center right has a diameter of about 80 kilometers (50 miles), making it comparable in size to the largest cities on Earth. The area within the outer boundary of the continuous bright ring is about 5,000 square kilometers (nearly 2,000 square miles). The diameter of the darker area within the bright ring is about 29 kilometers (18 miles), which is large enough to contain both the city of San Francisco and New York's Manhattan Island, side by side. The brightest reds in this image correspond to surfaces with high proportions of relatively pure water ice, while the blue colors indicate that non-ice materials are also present. The composition of the darker materials is controversial, they may consist of minerals formed by evaporation of salty brines, or they may be rich in sulfuric acid. The bright ring is a blanket of ejecta that consists of icy subsurface material that was blasted out of the crater by the impact, while the darker area in the center may retain some of the materials from the impacting body. Further study may yield new insights about both the nature of the impactor and the surface chemistry of Europa. Europa's surface is a question of great interest at present, since an ocean of liquid water may exist beneath the icy crust, possibly providing an environment suitable for life. Geologic investigations of Europa's surface are underway, and a new spacecraft mission, the Europa Orbiter, is planned. Impact craters with diameters of 20 kilometers (12 miles) and larger are extremely rare on Europa, as of 1999 only 7 such features were known. The rarity of larger impact craters on Europa lends greater significance to the discovery of this one. Impact crater counts are often employed to estimate the ages of the exposed surfaces of planets and satellites, and the small number of craters found on Europa implies that the surface may be quite young in geological terms. Thus the discovery of this feature may provide additional insights into questions about the age and level of geological activity of Europa's surface. Impact craters are expected to form with greater frequency on the "leading" sides of satellites that always turn the same face to their primary planet, in this case, Jupiter. The process is much like the effect of running through a rainstorm. The "apex" of Europa's leading side is located on the equator at 90 degrees West longitude, only about 10 degrees removed from the feature shown. Europa's leading side does not receive a continuous bombardment by ionized particles carried along by Jupiter's rapidly rotating magnetosphere (as is the case for the trailing side), which may allow greater preservation of the chemical, signatures of the impacting object. To the east of the bright ring-like feature are two, or perhaps three, similar but less well-defined quasi-circular features, raising the possibility that this crater is one member of a catena, or chain of craters. This would lend still greater interest to this area as a potential target for focused investigations by later missions such as the Europa Orbiter. The near-infrared mapping spectrometer on board Galileo obtained this image on May 31,1998, during that spacecraft's 15th orbital encounter with Europa. The image data was returned to Earth in several segments during both the 15th and the 16th orbital periods. Merging and processing of the full data set was accomplished in 1999. Analysis and interpretation are ongoing. Galileo has been orbiting Jupiter and its moons since December 1995. Its primary mission ended in December 1997, and after that Galileo successfully completed a two-year extended mission. The spacecraft is in the midst of yet another extended journey called the Galileo Millennium Mission. More information about the Galileo mission is available at:http://galileo.jpl.nasa.gov [ http://galileo.jpl.nasa.gov ]JPL manages Galileo for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena.
Sulphur Dioxide on the Chaac …
PIA02559
Jupiter
Near Infrared Mapping Spectr …
Title Sulphur Dioxide on the Chaac Region of Io
Original Caption Released with Image This image shows the Chaac region, on Jupiter's moon Io, viewed by two instruments on NASA's spacecraft Galileo during the flyby on February 22, 2000. On the left is an image taken by Galileo's onboard camera. On the right is a map of the relative abundance of sulphur dioxide obtained from an observation made by the infrared spectrometer, an instrument onboard Galileo. The right map shows that the bright white material inside the small caldera just to the east of Chaac (lower right in the camera image) is filled by sulphur dioxide. This sulphur dioxide is purer than at any other location so far observed on Io. It may represent a frozen layer of sulphur dioxide ice on the floor of the caldera. The width of the image seen on the right map is about 100 kilometers (62 miles). The Jet Propulsion Laboratory, Pasadena, Calif., manages the mission for NASA's Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology in Pasadena. This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page athttp://galileo.jpl.nasa.gov [ http://galileo.jpl.nasa.gov ]. Background information and educational context for the images can be found at http://galileo.jpl.nasa.gov/gallery/io.cfm [ http://galileo.jpl.nasa.gov/gallery/io.cfm ].
Io's Tvashtar Area in Infrar …
PIA02594
Jupiter
Near Infrared Mapping Spectr …
Title Io's Tvashtar Area in Infrared: Multiple Lava Flows
Original Caption Released with Image New and older lava flows clustered in the Tvashtar region of Jupiter's moon Io appear as hot spots in a temperature map from NASA's Galileo spacecraft. The multiple hot spots indicate continuing shifts in the location of Tvashtar's eruptions since the region's volcanic activity was first seen in December 1999. The temperature map (top) uses infrared observations made during Galileo's Aug. 6, 2001, flyby of Io. It is shown using landmarks from a February 2000 visible-light image (bottom) that Galileo's camera recorded of the Tvashtar area of bowl-like depressions in Io's northern hemisphere. The temperature map comes from Galileo's near-infrared mapping spectrometer. Tvashtar has been a very active region since December 1999, when Galileo detected a major eruption from the location marked A (See insert image below). The eruption from A was interpreted as a row of lava fountains. When Galileo flew by Io again in February 2000, the eruption had shifted to the location marked B, where a lava flow shaped like a dolphin's tail is seen. The temperature map shows that volcanic activity is present at many locations in this region. The highest temperatures are found in the three locations marked x, where new lavas may have recently come to the surface. Temperatures (in Kelvin) displayed in the color bar are lower limits. (The range in Fahrenheit is from 460 degrees below zero to 530 degrees above zero.) Each picture element averages the characteristics of an area about 2 kilometers (1.2 miles) across, smaller patches may be hundreds of degrees higher. The Galileo camera did not obtain a visible-light image of the Tvashtar region during the August 2001 flyby. Based on the locations of the hottest materials detected by Galileo's near-infrared mapping spectrometer, volcanologists expect that significant surface changes have occurred.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. Additional information about the spacecraft and its discoveries is available on the Galileo home page at http://galileo.jpl.nasa.gov [ http://galileo.jpl.nasa.gov ].
Io's Tvashtar Area in Infrar …
PIA02594
Jupiter
Near Infrared Mapping Spectr …
Title Io's Tvashtar Area in Infrared: Multiple Lava Flows
Original Caption Released with Image New and older lava flows clustered in the Tvashtar region of Jupiter's moon Io appear as hot spots in a temperature map from NASA's Galileo spacecraft. The multiple hot spots indicate continuing shifts in the location of Tvashtar's eruptions since the region's volcanic activity was first seen in December 1999. The temperature map (top) uses infrared observations made during Galileo's Aug. 6, 2001, flyby of Io. It is shown using landmarks from a February 2000 visible-light image (bottom) that Galileo's camera recorded of the Tvashtar area of bowl-like depressions in Io's northern hemisphere. The temperature map comes from Galileo's near-infrared mapping spectrometer. Tvashtar has been a very active region since December 1999, when Galileo detected a major eruption from the location marked A (See insert image below). The eruption from A was interpreted as a row of lava fountains. When Galileo flew by Io again in February 2000, the eruption had shifted to the location marked B, where a lava flow shaped like a dolphin's tail is seen. The temperature map shows that volcanic activity is present at many locations in this region. The highest temperatures are found in the three locations marked x, where new lavas may have recently come to the surface. Temperatures (in Kelvin) displayed in the color bar are lower limits. (The range in Fahrenheit is from 460 degrees below zero to 530 degrees above zero.) Each picture element averages the characteristics of an area about 2 kilometers (1.2 miles) across, smaller patches may be hundreds of degrees higher. The Galileo camera did not obtain a visible-light image of the Tvashtar region during the August 2001 flyby. Based on the locations of the hottest materials detected by Galileo's near-infrared mapping spectrometer, volcanologists expect that significant surface changes have occurred.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. Additional information about the spacecraft and its discoveries is available on the Galileo home page at http://galileo.jpl.nasa.gov [ http://galileo.jpl.nasa.gov ].
Hot Spots on Io
PIA02591
Jupiter
Near Infrared Mapping Spectr …
Title Hot Spots on Io
Original Caption Released with Image Volcanic hot spots, including a bright one never seen before, pepper an infrared color-coded image (left) of Jupiter's moon Io, taken by NASA's Galileo spacecraft on Aug. 6, 2001. The bright, new hot spot (arrow) in Io's high northern latitudes is the source of a towering volcanic plume detected in new images taken by Galileo's camera. Snowflake-like particles of clumped sulfur-dioxide molecules from the plume were caught by the plasma-science instrument onboard the spacecraft. Beginning about two hours after the spacecraft passed within 194 kilometers (120 miles) of Io's surface, Galileo's near-infrared mapping spectrometer recorded this image of most of the sunlit disc of the large, sizzling moon. The image shows the brightness of features at a wavelength of 4.4 microns, which detects heat from Io's many volcanic eruptions. An earlier image from Galileo's camera showing the same face of Io (right) is included for correlating the heat-sensing infrared data with geological features apparent in visible wavelengths. Many volcanic hot spots appear in the infrared image as bright regions: yellow to red to white, in order of increasing intensity. The brightest hot spot in the northern hemisphere, indicated by the arrow, was so vigorous at the time of the observation that some pixels (shown in black) were saturated. This hot spot was not a previously known volcano. Io has 108 known hot spots, 10 of which were discovered from this observation. Most of the newly discovered ones are too faint to show up in this map, but their thermal signatures can be detected by examining each location's infrared data at more than one wavelength. 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. 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 ].
Io's Loki in Infrared: Hot E …
PIA02595
Jupiter
Near Infrared Mapping Spectr …
Title Io's Loki in Infrared: Hot Edge
Original Caption Released with Image High temperatures observed by NASA's Galileo spacecraft along the western edge of the Loki volcano on Jupiter's moon Io may indicate freshly exposed material at the shore of a lava lake. Two temperature maps of the southern portion of Loki show hot (lower right) and hotter (upper right) features based on infrared-wavelength observations during an Oct. 16, 2001, flyby of Io. For context, they are shown beside a visible-wavelength picture (left) of the area taken during an earlier flyby. Loki is the most powerful volcano on Io. It has been active since at least 1979, when it was discovered by NASA's Voyager mission. Loki's dark volcanic crater, called a caldera, surrounds a light-colored island, as seen in the camera image (left). Previous observations by Galileo's instruments have shown that active lavas and still-cooling lava flows cover the floor of the caldera. In contrast, the island is cold and has no volcanic activity except in a narrow dark region that may be a crack or valley. Current volcanic activity appears in the two temperature maps from Galileo's near-infrared mapping spectrometer instrument. The lower right image shows where the surface is glowing at an infrared wavelength of 4.4 microns, with the yellow-orange coding correlated to temperatures of about 360 degrees Kelvin (188 Fahrenheit) and the reddish coding correlated to temperatures of about 430 Kelvin (314 Fahrenheit). The upper right image is at a wavelength of 2.5 microns, with the white streak correlated to temperatures of roughly 840 Kelvin (1,052 Fahrenheit). Each picture element averages the characteristics of an area about 2 kilometers (1.2 miles) across, smaller patches may be hundreds of degrees higher. Loki has puzzled scientists trying to determine what type of volcano it is. One idea holds it is an active lava lake with molten material under the crust. A competing view is it is a caldera whose floor is continuously flooded by lavas in successive flows. The concentration of higher temperatures along the western edge in the 2.5 micron map favors the lava lake idea. The cooler crust of molten lava lakes on Earth, such as on Hawaii's Kilauea volcano, tends to drift outward and hit against the caldera wall. This causes the crust next to the wall to break up, exposing hotter material from underneath. 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. Additional information about the spacecraft and its discoveries is available on the Galileo home page at http://galileo.jpl.nasa.gov [ http://galileo.jpl.nasa.gov ].
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