Astronomy Picture of the Day Search Results for "Mars AND Global AND Surveyor"

APOD: 2022 September 17 - Perseverance in Jezero Crater s Delta
Explanation: The Perseverance rover's Mastcam-Z captured images to create this mosaic on August 4, 2022. The car-sized robot was continuing its exploration of the fan-shaped delta of a river that, billions of years ago, flowed into Jezero Crater on Mars. Sedimentary rocks preserved in Jezero's delta are considered one of the best places on Mars to search for potential signs of ancient microbial life and sites recently sampled by the rover, dubbed Wildcat Ridge and Skinner Ridge, are at lower left and upper right in the frame. The samples taken from these areas were sealed inside ultra-clean sample tubes, ultimately intended for return to Earth by future missions. Starting with the Pathfinder Mission and Mars Global Surveyor in 1997, the last 25 years of a continuous robotic exploration of the Red Planet has included orbiters, landers, rovers, and a helicopter from planet Earth.

APOD: 2017 December 19 - The Spiral North Pole of Mars
Explanation: Why is there a spiral around the North Pole of Mars? Each winter this pole develops a new outer layer about one meter thick composed of carbon dioxide frozen out of the thin Martian atmosphere. This fresh layer is deposited on a water-ice layer that exists year round. Strong winds blow down from above the cap's center and swirl due to the spin of the red planet -- contributing to Planum Boreum's spiral structure. The featured image is a perspective mosaic generated earlier this year from numerous images taken by ESA's Mars Express and elevations extracted from the laser altimeter aboard NASA's Mars Global Surveyor mission. New missions to Mars planned in the next few years include Insight with plans to drill into Mars, and ExoMars and the Mars 2020 Rover with plans to search for signs of microscopic Martian life -- past and present.

APOD: 2010 August 15 - Layered Hills in Arabia Terra on Mars
Explanation: Why are some hills on Mars so layered? The answer is still under investigation. Clearly, dark windblown sand surrounds outcropping of light sedimentary rock across the floor of crater Arabia Terra. The light rock clearly appears structured into many layers, the lowest of which is likely very old. Although the dark sand forms dunes, rippled dunes of lighter colored sand are easier to see surrounding the stepped mesas. Blown sand possibly itself eroded once-larger mesas into the layered hills. Most of the layered shelves are wide enough to drive a truck around. The above image, showing an area about 3 kilometers across, was taken in 2003 October by the now defunct Mars Global Surveyor spacecraft orbiting Mars.

APOD: 2009 November 29 - Ancient Layered Hills on Mars
Explanation: Is this a picture of Mars or Earth? Oddly enough, it is a picture of Mars. What may appear to some as a terrestrial coastline is in fact a formation of ancient layered hills and wind-blown sand on Mars. The above-pictured region spans about three kilometers in Schiaparelli Crater. What created the layers of sediment is still a topic of research. Viable hypotheses include ancient epochs of deposit either from running water or wind-blown sand. Winds and sandstorms have smoothed and eroded the structures more recently. The "water" that appears near the bottom is actually dark colored sand. The image was taken with the Mars Global Surveyor spacecraft that operated around Mars from 1996-2006 and returned over 200,000 images.

APOD: 2007 September 28 - A Hole in Mars Close Up
Explanation: In a close-up from the HiRISE instrument onboard the Mars Reconnaissance Orbiter, this mysterious dark pit, about 150 meters across, lies on the north slope of ancient martian volcano Arsia Mons. Lacking raised rims and other impact crater characteristics, this pit and others like it were originally identified in visible light and infrared images from the Mars Odyssey and Mars Global Surveyor spacecraft. While the visible light images showed only darkness within, infrared thermal signatures indicated that the openings penetrated deep under the martian surface and perhaps were skylights to underground caverns. In this later image, the pit wall is partially illuminated by sunlight and seen to be nearly vertical, though the bottom, at least 78 meters below, is still not visible. The dark martian pits are thought to be related to collapse pits in the lava flow, similar to Hawaiian volcano pit craters.

APOD: 2007 April 21 - 3D Face on Mars
Explanation: Get out your red/blue glasses and gaze down on this weathered mesa on Mars. Of course, described as a rock formation that resembles a human head in a 1976 NASA press release, this mesa is also famous as the Face on Mars. The sharp stereo image was created by combining high resolution pictures from cameras on two different spacecraft in Mars orbit - Mars Reconnaissance Orbiter and Mars Global surveyor. It shows rugged details of the approximately 2 kilometer wide, isolated hill - similar to mesa landforms on planet Earth - rising some 240 meters above the plains of the martian Cydonia region. This remarkable 3D view exaggerates the hill's vertical dimensions.

APOD: 2006 December 12 - Light Deposits Indicate Water Flowing on Mars
Explanation: What's creating light-toned deposits on Mars? Quite possibly -- water! Images of the same parts of mid-latitude Mars taken over the years but released only last week have shown unexpected new light-toned deposits where there were none before. One clear case is shown above, where the same crater on Mars is shown as photographed in 1999 August and again in 2005 September. The unusual deposit is visible only on the more recent photograph. Apparent tributaries near the bottom bolster the leading hypothesis that water gushed out of the crater wall, flowed down the crater, and soon evaporated into the thin Martian atmosphere. Although frozen water-ice has been known near the Martian poles for years, free flowing surface water like this was not expected to be seen in the mid-latitudes of Mars. If confirmed, such water springs might make more of Mars hospitable to life and human visitation than previously believed.

APOD: 2006 March 25 - Northern Spring on Mars
Explanation: Astronomical spring came to planet Earth's northern hemisphere this week (and autumn to the south) with the equinox on March 20th. But on Mars, northern spring began on January 22nd. Still in northern springtime, the Red Planet currently has a similar appearance to this composite of images from previous years taken by the long-lasting Mars Global Surveyor spacecraft. The sprawling dark region near picture center is Syrtis Major, with the whitish Hellas impact basin just below, in the southern hemisphere. The four seasons on Earth each last about 90 earth days, while Mars' larger and more eccentric elliptical orbit results in seasons that are longer and vary more widely in length - from about 140 to 190 martian sols.

APOD: 2005 September 17 - The Shadow of Phobos
Explanation: Hurtling through space above the Red Planet, potato-shaped Phobos completes an orbit of Mars in less than eight hours. In fact, since its orbital period is shorter than the planet's rotation period, Mars-based observers see Phobos rise in the west and set in the east - traveling from horizon to horizon in about 5 1/2 hours. These three images from the Mars Global Surveyor (MGS) spacecraft record the oval shadow of Phobos racing over western Xanthe Terra on August 26, 1999. The area imaged is about 250 kilometers across and is seen in panels from left to right as red filter, blue filter, and combined color composite views from the MGS wide-angle camera system. The three dark spots most easily seen in the red filter image are likely small fields of dark sand dunes on crater floors. Standing in the shadow of Phobos, you would see the Martian version of a solar eclipse!

APOD: 2004 July 14 - Polar Polygons on Mars
Explanation: What's the best way to the city center? What looks like a street map of some city on Earth is actually a series of naturally-formed fragmented polar polygons on Mars. The existence of polar polygons on Mars is particularly interesting as they may indicate regions where water ice lies within a few meters of the surface. Similar looking polygons are commonly found in the arctic and Antarctic of Earth, where they typically form from a repetitive cycle of freezing and thawing. The above image spans a distance of about 3 kilometers and was taken recently by the orbiting Mars Global Surveyor.

APOD: 2004 May 19 - Brain Crater on Mars
Explanation: What caused this unusual looking crater floor on Mars? Appearing at first glance to resemble the human brain, the natural phenomena that created the unusual texture on the floor of this Martian impact crater are currently under investigation. The light colored region surrounding the brain-textured region is likely sand dunes sculpted by winds. The Mars Global Surveyor robot spacecraft that has been orbiting Mars since 1997 took the above image. Meanwhile, down on the surface, robots Spirit and Opportunity continue to roll, inspecting landscape, rocks, and soil for clues to the ancient watery past of the red planet. Humorously, this brain-terrain on Mars spans about a kilometer, making it just about the right size to fit inside the rock formation once dubbed the Face on Mars.

APOD: 2004 January 24 - Valles Marineris from Mars Express
Explanation: Looking down from orbit on January 14, ESA's Mars Express spacecraft scanned a 1700 by 65 kilometer swath across Valles Marineris - the Grand Canyon of Mars - with its remarkable High Resolution Stereo Camera. This spectacular picture reconstructs part of the scanned region from the stereo colour image data recording the rugged terrain with a resolution of 12 metres per pixel. Joining Mars Global Surveyor and Mars Odyssey, Mars Express has been orbiting the red planet since December 25th, returning scientific data, acting as a communications relay, and even making coordinated atmospheric observations with NASA's Spirit rover on the surface. The Beagle 2 lander was released from Mars Express making a landing attempt also on December 25th, but no signal has been received so far.

APOD: 2004 January 14 - A Mars Panorama from the Spirit Rover
Explanation: If you could stand on Mars -- what would you see? Scrolling right will reveal a full color 360-degree panoramic view from NASA's Spirit Rover that landed on Mars just 10 days ago. The image is a digital mosaic from the panoramic camera that shows the view in every direction. Annotated on the image are the directions and distances to various hills along the horizon. These hills are valuable for orienting Spirit since they are also visible to the Mars Global Surveyor and Mars Odyssey spacecraft orbiting high overhead. Visible in the foreground are several instruments and airbags around Columbia Memorial Station. Spirit will attempt to roll onto the red planet in the next few days and explore interesting features.

APOD: 2003 December 24 - Layered Hills on Mars
Explanation: Why are some hills on Mars so layered? The answer is still under investigation. Clearly, dark windblown sand surrounds outcropping of light sedimentary rock across the floor of crater Arabia Terra. The light rock clearly appears structured into many layers, the lowest of which is likely very old. Although the dark sand forms dunes, rippled dunes of lighter colored sand are easier to see surrounding the stepped mesas. Blown sand possibly itself eroded once-larger mesas into the layered hills. Most of the layered shelves are wide enough to drive a truck around. The above image, showing an area about 3 kilometers across, was taken in October by the Mars Global Surveyor spacecraft currently orbiting Mars. Tomorrow, the first of three robot spacecraft from Earth is scheduled to arrive at the red planet.

APOD: 2003 August 28 - Mars Rising Behind Elephant Rock
Explanation: Yesterday, at about 10 am Universal Time, Mars and Earth passed closer than in nearly 60,000 years. Mars, noticeably red, remains the brightest object in the eastern sky just after sunset. The best views of Mars, however, will continue to be from the robot spacecraft currently orbiting Mars: the Mars Global Surveyor and the Mars Odyssey. The current pass sparked the launching of four new spacecraft toward Mars, some of which will deploy landers early next year and likely return even more spectacular views of our planetary neighbor. Pictured above, Mars was photographed rising in the southeast behind Elephant Rock in the Valley of Fire State Park, Nevada, USA.

APOD: 2003 July 30 - Frosty Mountains on Mars
Explanation: What causes the unusual white color on some Martian mountains? The answer can be guessed by noticing that the bright areas disappear as springtime takes hold in the south of Mars: dry ice. Dry carbon dioxide ice sublimates directly to gas from its frozen state. The frosty mountains, named Charitum Montes, have been covered with carbon dioxide ice over the Martian winter. The serene scene pictured above is not a photograph, but rather a computationally constructed digital illusion resulting from the fusion of two color images from the Mars Orbital Camera and topographic data from the Mars Orbiter Laser Altimeter. Both instruments operate from the Mars Global Surveyor robot spacecraft currently orbiting Mars. The red planet continues to grow larger in terrestrial skies as Earth and Mars move closer to their recent-record closest approach on August 27.

APOD: 2003 July 10 - Dust Storm Over Northern Mars
Explanation: Almost on cue, as Mars nears its closest approach to planet Earth in recorded history, ominous seasonal dust storms are beginning to kick up. Observers worry that the activity may presage the development of a planet wide dust storm, frustrating attempts to view Mars in the coming months, a situation similar to the Red Planet's uncooperative behavior in 2001. In this example, recorded in mid-May by the Mars Global Surveyor spacecraft camera, a dust storm the size of a continent sweeps north and east (toward the upper right) across Mars' northern Acidalia Planitia. Meanwhile, interplanetary robotic explorers Mars Express/ Beagle 2, Nozomi, and the twin Mars Exploration Rovers Opportunity and Spirit, are all bound for Mars and should arrive by early January 2004.

APOD: 2003 July 1 - Martian Moon Phobos from MGS
Explanation: Why is Phobos so dark? Phobos, the largest and innermost of two Martian moons, is the darkest moon in the entire Solar System. Its unusual orbit and color indicate that it may be a captured asteroid composed of a mixture of ice and dark rock. The above picture was captured recently by the robot spacecraft Mars Global Surveyor (MGS) orbiting Mars. Phobos is a heavily cratered and barren moon, with its largest crater located on the far side. From MGS images like this, Phobos has been determined to be covered by perhaps a meter of loose dust. Phobos orbits so close to Mars that from some places it would appear to rise and set twice a day, but from other places it would not be visible at all. Phobos' orbit around Mars is continually decaying -- it will likely break up with pieces crashing to the Martian surface in about 50 million years.

APOD: 2003 June 2 - The Fogs of Mars
Explanation: Fogs of clouds and dust covered parts of southern Mars during last Martian winter. Giant volcanoes, such as Ascraeus Mons, the central circular feature near the top of the image, were surrounded by large water clouds. Slightly southwest, Pavonis Mons and Arisa Mons also peeked above their water clouds. The rough terrain below center is Labyrinthus Noctis, a maze of deep troughs running over 200 kilometers long. Directly south, a large white dust storm fogs Syria Planum, a large plateau. This image mosaic was taken by the Mars Global Surveyor spacecraft currently orbiting Mars. Soon, five more Earth-launched spacecraft should arrive at the Red Planet, named for the Roman god of war.

APOD: 2003 May 26 - The Earth and Moon from Mars
Explanation: What does Earth look like from Mars? The first image of Earth from the red planet was captured earlier this month by the camera onboard the Mars Global Surveyor spacecraft currently orbiting Mars. Features visible on Earth include the Pacific Ocean, clouds, much of South America, and part of North America. Earth's Moon is visible on the upper right, with the crater Tycho brightening the lower part. Previously, Earth has been imaged from the Moon and spacecraft across the Solar System.

APOD: 2003 April 22 - Springtime on Mars
Explanation: Vast canyons, towering volcanoes, sprawling fields of ice, deep craters, and high clouds can all be seen in this image of the Solar System's fourth planet: Mars. The orbiting robot Mars Global Surveyor spacecraft took the above mosaic of images as springtime dawned in Northern Mars in 2002 May. Sprawled across the image bottom is Valles Marinaris, a canyon three times the length of Earth's Grand Canyon, and four times as deep. On the left are several volcanoes including Olympus Mons, a volcano three times higher than Earth's Mt. Everest. At the top is the North Polar Cap made of thawing water and carbon-dioxide based ice. Swirling white clouds and circular impact craters are also visible around Mars. Two rovers will be launched to Mars this summer and should arrive in 2004 January.

APOD: 2003 March 29 - The Shadow of Phobos
Explanation: Hurtling through space above the Red Planet, potato-shaped Phobos completes an orbit of Mars in less than eight hours. In fact, since its orbital period is shorter than the planet's rotation period, Mars-based observers see Phobos rise in the west and set in the east - traveling from horizon to horizon in about 5 1/2 hours. These three images from the Mars Global Surveyor (MGS) spacecraft record the oval shadow of Phobos racing over western Xanthe Terra on August 26, 1999. The area imaged is about 250 kilometers across and is seen in panels from left to right as red filter, blue filter, and combined color composite views from the MGS wide-angle camera system. The three dark spots most easily seen in the red filter image are likely small fields of dark sand dunes on crater floors. Standing in the shadow of Phobos, you would see the Martian version of a solar eclipse!

APOD: 2003 February 5 - Unusual Gullies and Channels on Mars
Explanation: What could have formed these unusual channels? Inside Newton Basin on Mars, numerous narrow channels run from the top down to the floor. The above picture covers a region spanning about 1500 meters across. These and other gullies have been found on Mars in recent high-resolution pictures taken by the orbiting Mars Global Surveyor robot spacecraft. Similar channels on Earth are formed by flowing water, but on Mars the temperature is normally too cold and the atmosphere too thin to sustain liquid water. Nevertheless, many scientists hypothesize that liquid groundwater can sometimes surface on Mars, erode gullies and channels, and pool at the bottom before freezing and evaporating. If so, life-sustaining ice and water might exist even today below the Martian surface -- water that could potentially support a human mission to Mars. Research into this exciting possibility is sure to continue!

APOD: 2002 December 24 - Spring Dust Storms at the North Pole of Mars
Explanation: Spring reached the north pole of Mars in May, and brought with it the usual dust storms. As the north polar cap begins to thaw, a temperature difference occurs between the cold frost region and recently thawed surface, resulting in swirling winds between the adjacent regions. In the above image mosaic from the Mars Global Surveyor spacecraft currently orbiting Mars, the white material is frozen carbon dioxide that covers much of the extreme north. The choppy clouds of at least three dust storms can be identified.

APOD: 2002 October 24 - Gullies on Mars
Explanation: The Gullies of Mars would probably not have been sensational enough for the title of a vintage Edgar Rice Burroughs story about the Red Planet. But it would get the attention of planetary scientists today. First identified in high resolution images of Mars recorded by the orbiting Mars Global Surveyor spacecraft, the gullies are interpreted as startling evidence that liquid water flowed across the martian surface in geologically recent times. Similar channels on Earth are formed by flowing water, but on Mars the temperature is normally too cold and the atmosphere too thin to sustain liquid water. Still, it is thought possible that water did burst out from underground layers and remain liquid long enough to erode the gullies, while alternative explanations suggest the erosion was produced by a flowing jumble of solid and gaseous carbon dioxide. Spanning a few kilometers along the wall of an impact crater this high resolution image from Mars Global Surveyor shows typical martian gullies near the top of the crater wall giving way to sand dunes toward the crater floor. Whitish frost is visible near the top and on the dark sand dunes below. The muted colors were synthesized from wide angle image data.

APOD: 2002 October 1 - Rectangular Ridges on Mars
Explanation: What could cause rectangular ridges on Mars? As data flows in from the two spacecraft currently orbiting Mars, surface structures are seen that are not immediately understood. These structures pose puzzles that planetary geologists are eager to solve, as they might provide clues to past processes that have shaped Mars over billions of years. On the right of the above image is an unusual array of ridges first spotted in Mariner 9 data in 1972. A ridge wall runs for about 5 kilometers. Two competing progenitor theories include hardened sand dunes and once-molten rock that seeped through surface cracks and cooled. Dubbed "Inca City" for their resemblance to stone walls of an ancient Earth civilization, the new Mars Global Surveyor images now show them to be part of a larger circular pattern, indicating an origin possibly related to the impact crater. (Non-natural origin hypotheses are not invoked by conservative scientists unless clear indications exist that natural processes could not work.)

APOD: 2002 September 3 - A Dust Devil on Mars
Explanation: Does the surface of Mars change? When inspecting yearly images of the Martian surface taken by the robot spacecraft Mars Global Surveyor currently orbiting Mars, sometimes new dark trails are visible. Although originally a mystery, the culprit is now usually known to be a dust devil, a huge swirling gas-cloud with similarities to a terrestrial tornado. Pictured above, a recent image has not only captured a new dark trail but the actual dust devil itself climbing a crater wall. Dust devils are created when Martian air is heated by a warm surface and begins to spin as it rises. Dust devils can stretch 8 kilometers high but usually last only a few minutes.

APOD: 2002 August 8 - Ancient Volcanos of Mars
Explanation: Findings of ancient martian microbial fossils in meteorites and liquid water related features on Mars' surface are currently controversial issues. But one thing long established by space-based observations of the Red Planet is the presence of volcanos, as Mars supports some of the largest volcanos in the solar system. This synthetic color picture recorded in March by the Mars Global Surveyor spacecraft shows two of them, Ceraunius Tholus (leftmost) and Uranius Tholus. Found north of the Tharsis region of truly large martian volcanos, these are actually two relatively small volcanos, Ceraunius Tholus being only about the size of the Big Island of Hawaii on planet Earth. Impact craters which overlay the volcanic martian terrain indicate that these volcanos are themselves ancient and inactive. North is to the right and the scene is illuminated by sunlight from the top left. A light region of dust deposited by recent global dust storms lies on the lower left flank of Ceraunius Tholus, whose summit crater is about 25 kilometers across.

APOD: 2002 June 27 - Carving Ma'adim Vallis
Explanation: Just as erosion from the Colorado River carved the Grand Canyon on Earth, a river of flood water may have carved Ma'adim Vallis, one of the largest canyons on Mars. Researchers have presented strong evidence for such a scenario based on elevation data recorded by the MOLA (Mars Orbiter Laser Altimeter) experiment on the Mars Global Surveyor spacecraft. This false-color, detailed, topographical map of MOLA data shows in blue the area of an enormous complex of lakes that are thought to have existed over three and a half billion years ago in the southern highlands of Mars. As the largest lake spilled over the low point in its boundary a torrential flood would have moved north, along the direction indicated by the arrow, carving the sinuous Ma'adim Vallis. At the north end of Ma'adim Vallis, the flood waters would have poured into large, round Gusev Crater. Since standing bodies of surface water are thought to be favorable for ancient martian microbial life, Gusev Crater has been suggested as a landing site for future Mars missions.

APOD: 2002 June 4 - A Martian Metamorphosis
Explanation: Is it an Escher, or Mars? Three different types of surfaces visible in the North Polar Cap of Mars morph into each other in a way perhaps reminiscent of the works of M. C. Escher. On the far left dark sand covers the ground, while the center shows a transition to a dune field. On the far right a transition is made to a much lighter surface, likely containing a larger amount of ice. Shadows indicate that lighter material holds the higher ground, with some steep cliffs on the divide. Dune shapes indicate that wind typically blows toward the upper left. Mars Global Surveyor, one of two robot spacecraft currently orbiting Mars, took the above image in early 2001. Recent images from the other orbiter, Mars Odyssey, have bolstered the hypothesis that a significant amount of water-ice lies beneath the surface near the Martian South Pole.

APOD: 2002 February 19 - Water Ice Imaged in Martian Polar Cap
Explanation: Does water exist today on Mars? Yes, although the only place on Mars known to have water is the North Polar Cap, and that water is frozen. Views of this potentially life-enabling water-ice are usually obscured -- in the winter by darkness and in the summer by clouds. Last April, however, the orbiting Mars Global Surveyor spacecraft was able to get a good glimpse of the water-bearing cap just before Martian spring. Low, dark layers in the above image are thought to contain a large amount of sand, while high, light layers likely contain higher amounts of water-ice. The image spans an area about 5 kilometers across.

APOD: 2001 December 13 - The South Pole of Mars
Explanation: The south pole of Mars is the bright area near the center of the detailed, subtly shaded color image above. Recorded in September of this year by the Mars Global Surveyor (MGS) spacecraft, the picture shows a region surrounding the 400 kilometer wide martian polar cap in the midst of southern hemisphere spring. During this season the ice cap, predominantly layers of frozen carbon dioxide (dry ice) plus some water ice, begins to shrink as the ices change directly from solid to gas (sublimate). Hazy clouds of ice crystals and fog, extend across the bottom of the picture and a darker, more defrosted area is visible at the upper right, near the Red Planet's night side. A wealth of MGS data has allowed changes in the extent and density of the ice cap to be tracked over time. Now, researchers are also reporting indications that, in addition to seasonal changes, overall the martian southern ice cap has been dwindling in recent years -- dramatic evidence of a changing martian climate. At the measured rate, the increasing amount of carbon dioxide released could gradually raise Mars' atmospheric pressure, doubling it over hundreds to thousands of martian years.

APOD: 2001 November 27 - Ancient Layered Rocks on Mars
Explanation: Is this a picture of Mars or Earth? Oddly enough, it is a picture of Mars. What may appear to some as a terrestrial coastline is in fact a formation of ancient layered rocks and wind-blown sand on Mars. The above-pictured region spans about three kilometers in Schiaparelli Crater. What created the layers of sediment is still a topic of research. Viable hypotheses include ancient epochs of deposit either from running water or wind-blown sand. Winds and sandstorms have smoothed and eroded the structures more recently. The "water" that appears near the bottom is actually dark colored sand. The image was taken with the Mars Global Surveyor spacecraft that has now returned over 100,000 images.

APOD: 2001 October 17 - Mars Engulfed
Explanation: For months now, Mars has been engulfed by a great dust storm, the biggest seen raging across the Red Planet in decades. As a result, these two Hubble Space Telescope storm watch images from late June and early September offer dramatically contrasting views of the martian surface. At left, the onset of smaller "seed" storms can be seen near the Hellas basin (lower right edge of Mars) and the northern polar cap. A similar surface view at right, taken over two months later, shows the fully developed extent of the obscuring global dust storm. The storm is reported to be waning, but planet-wide effects such as the warming of the upper martian atmosphere and cooling of the surface are still being monitored daily by instruments on board the Mars Global Surveyor spacecraft. The present condition of the martian atmosphere is also important to the aerobraking Mars Odyssey spacecraft, scheduled to arrive at the Red Planet next week.

APOD: 2001 October 1 - A Global Dust Storm on Mars
Explanation: A dust storm on Mars can involve nearly the entire planet. As spring descended on the southern hemisphere of the red planet this June and July, a global dust storm raged. Pictured above is the storm on July 8 as it spread up from the south, oriented on the lower right. The image was captured by the robot Mars Global Surveyor spacecraft which continues to orbit the red planet. A smaller dust storm is visible in the north to the left of the dark giant volcano Ascraeus Mons. Far-reaching dust storms also occur on planet Earth.

APOD: 2001 August 15 - Mars: 3-D Dunes
Explanation: Get out your red/blue glasses and treat yourself to this dramatic 3-D view of sand dunes on Mars! The field of undulating dunes is found in Nili Patera, a volcanic depression in central Syrtis Major, the most prominent dark feature on the Red Planet. Two different images from the orbiting Mars Global Surveyor spacecraft were combined to make this stereo picture, one taken in March 1999 and the other recorded in April 2001. Sculpted by winds like the sand dunes of Earth, these particular Martian dunes show no change in shape over the time separating the two images, a period equivalent to about one Martian year. This cropped version of the 3-D picture spans an area around 2 kilometers across. Walking, you might cover that distance in about 20 minutes.

APOD: 2001 July 27 - Martian Dust Storm
Explanation: If you've been unhappy with the weather on Earth, check out Mars, now in the grip of a planet-wide dust storm. Above, observations from the orbiting Mars Global Surveyor (MGS) spacecraft illustrate the storm's progress through July 21. The series of dated frames show measurements from the MGS Thermal Emission Spectrometer which can determine both temperature and amount of atmospheric dust. Dust data has been plotted on maps of the martian surface with blue representing relatively clear atmosphere and red colors indicating increasing concentrations of dust. In mid June, scientists first noticed the beginnings of the storm in Mars' southern hemisphere and have watched it grow to obscure most of the planet. Unfortunately for Mars-watchers, the timing of the storm has hidden the Red Planet's surface from view during its period of close approach to planet Earth.

APOD: 2001 June 28 - The Topography of Mars
Explanation: Mars has its ups and downs. Visible on the above interactive topographic map of the surface of Mars are giant volcanoes, deep valleys, impact craters, and terrain considered unusual and even mysterious. Particularly notable are the volcanoes of the Tharsis province, visible on the left in (false-color) red and white, which are taller than any mountains on Earth. Just to the left of center is Valles Marineris, a canyon much longer and deeper than Earth's Grand Canyon. On the right in blue is the Hellas Planitia, a basin over 2000 kilometers wide that was likely created by a collision with an asteroid. Mars has many smooth lowlands in the north, and many rough highlands in the south. This map was created by the Mars Orbital Laser Altimeter (MOLA) on board the robot Mars Global Surveyor currently orbiting Mars. MOLA measures heights on Mars by precisely determining the time it takes for a low power laser beam to bounce off the surface. Zoom in by clicking anywhere on the above map.

APOD: 2001 June 26 - All of Mars
Explanation: From pole to pole, from east to west, this is all of Mars. The above picture was digitally reconstructed from over 200 million laser altimeter measurements taken by the Mars Global Surveyor spacecraft currently orbiting Mars. The image strips Mars of its clouds and dust, and renders the whole surface visible simultaneously in its true daytime color. Particularly notable are the volcanoes of the Tharsis province, visible on the left, which are taller than any mountains on Earth. Just to the left of center is Valles Marineris, a canyon much longer and deeper Earth's Grand Canyon. On the right, south of the center, is the Hellas Planitia, a basin over 2000 kilometers wide that was likely created by a collision with an asteroid. Mars has many smooth lowlands in the north, and many rough highlands in the south. Mars has just passed its closest approach to Earth since 1988 and can be seen shining brightly in the evening sky.

APOD: 2001 March 27 - Swiss Cheese Like Landscape on Mars
Explanation: Why do parts of the south pole of Mars look like swiss cheese? This little-understood landscape features flat-topped mesas nearly 4 meters high and circular indentations over 100 meters across. Since this swiss-cheese topography is unique to the polar cap covering southern Mars, exogeologists speculate that mesa composition might be high in frozen carbon dioxide (dry ice). Additionally, dry ice might have had a role in this strange landscape's creation. In the above picture, the Martian surface is illuminated by sunlight from the upper right. The above picture was taken in August 1999 by the robot Mars Global Surveyor spacecraft currently orbiting Mars.

APOD: 2001 February 26 - Sand Dunes on Mars
Explanation: Sand dunes on Mars can appear exotic. The dark dunes above might be compared to shark's teeth or chocolate confections. In reality, they arise from the complex relationship between the sandy surface and high winds on Mars. These particular dunes are located in Proctor Crater, a 170 kilometer wide crater first seen to house sand dunes by Mariner 9 more than 25 years ago. The above picture was taken by Mars Global Surveyor (MGS), a robot spacecraft currently in orbit around Mars. MGS has recently completed a primary goal of taking and transmitting detailed survey images of the red planet over an entire Martian year (669 Earth days). MGS will now be deployed to study particularly interesting regions of Mars in more detail.

APOD: 2000 December 5 - Layered Mars: An Ancient Water World
Explanation: Pictured above, layers upon layers stretch across the floor of West Candor Chasma within the immense martian Valles Marineris. Covering an area 1.5 by 2.9 kilometers, the full image from the Mars Global Surveyor spacecraft shows over 100 individual beds. Each strikingly uniform layer is smooth, hard enough to form steep edges, and is 10 to 11 meters thick. In a press conference yesterday scientists Michael Malin and Ken Edgett presented this and other new images which show that the layered patterns exist at widespread locations near the martian equator. Their results indicate that some of the layered regions may be 3.5 billion years old. On planet Earth, layered patterns like these are formed from sediment deposited over time by large bodies of water. Likewise, the layered beds on Mars may be sedimentary rock formed in ancient lakes and seas. The researchers caution, however, that other uniquely martian processes may be responsible for the layering. Did life arise on ancient Mars? Because of their possible association with water, a prime location for future searches for fossil remains of martian life would be within these layers of Mars.

APOD: 2000 December 1 - A Frosty Crater On Mars
Explanation: In the martian southern hemisphere, autumn has arrived. As on planet Earth, the cooler temperatures bring a seasonal frost to the landscape. Of course on Mars, the surface temperatures can be really cool, reaching below minus 100 degrees C. This detailed Mars Global Surveyor synthesized color image of Lowell crater at 52 degrees south martian latitude was recorded on October 17. Whitish frost has begun to accumulate on floor of the 201 kilometer wide crater. The crater's weathered walls suggest Lowell is relatively old. In striking contrast, two smaller, sharp-rimmed young craters are clearly superimposed on the older features near Lowell's outer rim.

APOD: 2000 November 14 - The Yardangs Of Mars
Explanation: OK, fans of classic science fiction might be disappointed. The yardangs are not barsoomian warriors in a newly discovered Edgar Rice Burroughs tale of adventure and conquest on the Red Planet. In fact yardangs, geologists' term for narrow, wind-eroded ridges, are common land features in the desert regions of planet Earth. Such Eolian (wind related) landforms are common on Mars too, and this recently released Mars Global Surveyor picture shows long, sculpted yardangs in the eastern Aeolis region of southern Elysium Planitia. These martian yardangs may have formed in deposits of volcanic ash. Covering a swath of the martian surface 2.5 kilometers high, this composite image does offer special effects, though. If you have red/blue glasses (red for the left eye) you can view the yardangs of Mars in astounding 3-D!

APOD: 2000 October 9 - A Polar Martian Dust Storm
Explanation: On August 29, a large dust storm was photographed erupting out from the north polar cap of Mars. Such dust storms are not uncommon as summer advances in the north. In the above picture taken by the Mars Global Surveyor spacecraft currently orbiting Mars, the white material is frozen carbon dioxide that covers much of the extreme north. As the north polar cap region begins to thaw, a temperature difference occurs between the cold frost region and recently thawed surface, resulting in swirling winds between the adjacent regions. Visible in the storm is a strong central jet about 900 kilometers long that is creating symmetric swirling vortices. Although winds can reach 100 km/hour, the thin atmosphere of Mars usually makes such storms less destructive than similar storms on Earth.

APOD: 2000 June 26 - Newton Crater: Evidence for Recent Water on Mars
Explanation: What could have formed these unusual channels? Inside a small crater that lies inside large Newton Crater on Mars, numerous narrow channels run from the top down to the crater floor. The above picture covers a region spanning about 3000 meters across. These and other gullies have been found on Mars in recent high-resolution pictures taken by the orbiting Mars Global Surveyor robot spacecraft. Similar channels on Earth are formed by flowing water, but on Mars the temperature is normally too cold and the atmosphere too thin to sustain liquid water. Nevertheless, many scientists now hypothesize that liquid water did burst out here from underground Mars, eroded the gullies, and pooled at the bottom as it froze and evaporated. If so, life-sustaining ice and water might exist even today below the Martian surface -- water that could potentially support a human mission to Mars. Research into this exciting possibility is sure to continue!

APOD: 2000 June 23 - The Gullies Of Mars
Explanation: The recently revealed gullies on Mars are rare. But they may prove to be sites of present day, near surface, liquid water, holding out the tantalizing possibility of martian life. Too small to have been seen by past Mars orbiters, these disconcerting landforms were found in only about 250 out of more than 20,000 high resolution images from the operating Mars Global Surveyor spacecraft. Gullies found so far are located away from the martian equatorial region at middle and high latitudes (predominately in the south) and on poleward facing slopes. They are disconcerting because researchers have a compelling body of evidence that the martian gullies are related to groundwater seepage and, like their terrestrial counterparts, liquid water runoff -- on a planet whose surface is thought to be too cold and atmosphere too thin for liquid water to exist. The gullies in the three kilometer wide area pictured above are in the south facing wall of a crater in southern Noachis Terra. Unblemished by craters and overlaying young surface features, these and other gullies are inescapably young themselves. In fact, future monitoring of the martian gullies for changes could demonstrate whether the flows that formed them are still active today.

APOD: 2000 May 29 - Olympus Mons Volcano on Mars
Explanation: Scroll right to virtually climb the largest volcano in the Solar System. Olympus Mons on Mars measures three times higher than Earth's highest mountain, and has a volume over fifty times greater than Earth's largest volcano. The caldera at the top is over 70 kilometers wide. The low gravity and relatively static surface crust on Mars allows structures as large as Olympus Mons to form. Surrounding the volcano is a cliff that ranges up to 10 kilometers high. This black & white image is one of over 20,000 just-released images taken by the robot spacecraft Mars Global Surveyor that continues to orbit Mars.

APOD: 2000 April 25 - Layers of the Martian South Polar Cap
Explanation: The South Pole of Mars is stranger than was previously thought. Pictured above are unexpectedly complex layers photographed recently by the Mars Global Surveyor spacecraft currently orbiting Mars. The layers probably include carbon dioxide ice, water ice, rock and dust. The intricate structures might indicate erosion patterns that hold clues to the history of the Martian climate over the past 100 million years. The above image covers a region five kilometers across, resolving details as small as 25 meters across.

APOD: 2000 March 23 - Inside Mars
Explanation: What's inside Mars? From orbit, the Mars Global Surveyor (MGS) spacecraft has recorded detailed images of the red planet since July 1997. Still, its cameras can not look beneath the surface. But minute changes in the spacecraft's orbital velocity are produced by variations in the planet's gravitational field, and these changes are related to interior density fluctuations. When the subtle orbital changes were measured using MGS radio science experiments and combined with the accurate Mars Orbiter Laser Altimeter topographical data, researchers were able to produce a map of the thickness of the martian crust. In this color cut-away diagram of the results, red colors correspond to thin and blue to thick areas of the crust which rides above the martian mantle. From the global map, the crust is seen to range from about 20 to 50 miles thick and shows a dramatic difference between the generally thinner northern hemisphere to thicker southern hemisphere crust. For the newly formed planet, the thin crust would have promoted rapid cooling and may have given rise to a large northern ocean on early Mars.

APOD: 2000 March 17 - Martian Dust Devil Trails
Explanation: Who's been marking up Mars? This portion of a recent high-resolution picture from the orbiting Mars Global Surveyor spacecraft shows twisting dark trails criss-crossing a relatively flat rippled region about 3 kilometers wide on the martian surface. Newly formed trails like these presented researchers with a tantalizing martian mystery but have now been identified as likely the work of miniature wind vortices known to occur on the red planet - martian dust devils. Another example of wind processes on an active Mars, dust devils had been detected passing near the Viking and Mars Pathfinder landers. Such spinning columns of rising air heated by the warm surface are common in dry and desert areas on planet Earth. Typically lasting only a few minutes, they becoming visible as they pick up loose dust. On Mars, dust devils can be up to 8 kilometers high and leave dark trails as they disturb the bright, reflective surface dust.

APOD: 2000 February 2 - Aeolian Mars
Explanation: Mars' atmosphere is relatively thin, still when martian winds blow they weather and shape its surface. Like familiar aeolian features on Earth, this field of dunes within Mars' Rabe crater exhibits graceful undulating ridges which can shift as windblown material is deposited on the dunes' windward face and falls away down the steeper leeward slopes. Indicated by the arrow, the dark trails are signs that the martian sand has avalanched down the steep slopes in the recent past. Rippling patterns of smaller dunes are also visible in this sharp high-resolution view along with criss-crossing dark trails which may be evidence of local dust-devil windstorms. The image is about 3 kilometers across and was recorded in March of 1999 by the orbiting Mars Global Surveyor spacecraft.

APOD: 2000 January 6 - Mars in the New Year
Explanation: Many will long remember where they were and what they were doing when the calendar rolled over to the year 2000. On Mars, of course, that date was nothing special and the Mars Global Surveyor spacecraft continued with business as usual - systematically recording images of the Red Planet from orbit. In fact, this striking high-resolution picture was taken less than 7 hours after the new year began for planet Earth's "Universal Time" zone. The area seen is about 3 kilometers across at a maximum resolution of 4.5 meters per pixel. It shows a wonderful variety of surface features and textures in the Martian northern hemisphere region Nilosyrtis Mensae.

APOD: December 4, 1999 - Mars Polar Lander Target Ellipse
Explanation: South is up in this recent composite color picture of Mars Polar Lander's target region near the Martian South Pole taken on November 28. Imaged by the orbiting Mars Global Surveyor's wide angle camera, the area covered is 105 kilometers across with the expected landing ellipse superposed. It is late spring in Mars' southern hemisphere and white patches near the top are what remains of the area's winter frost while dark areas are likely sand and fields of sand dunes. The Mars Polar Lander spacecraft reached the Red Planet yesterday at 20:00 UTC and earthbound controllers are still trying to establish contact with the lander during the available communication windows. From orbit, the Mars Global Surveyor spacecraft will try to contact the two basketball-sized microprobes jettisoned during the lander's descent.

APOD: December 3, 1999 - Southern Mars
Explanation: This topographical map of the southern hemisphere of Mars was generated using data from the Mars Orbiter Laser Altimeter (MOLA). Flying on the Mars Global Surveyor spacecraft, MOLA has bounced a laser beam off the Martian surface over 200,000,000 times producing a wealth of detailed elevation measurements. The MOLA measurements have been color-coded so, for example, the white areas at left are the highest elevations in the southern Tharsis region and not snow-covered peaks. These areas are more than 6 kilometers above the hypothetical Martian "sea-level". Likewise, deep blues and purples are not water oceans but correspond to the lowest elevations (more than 4 kilometers below "sea-level"), like those found within the giant Hellas impact basin at right. In fact, liquid water is not present on Mars' surface today, but may have been in the past. NASA's Mars Polar Lander spacecraft is scheduled to embark on an investigation of the role of water in the climate history of the Red Planet. The lander is targeted to touch down within the long, thin ellipse indicated here just below the Martian South Pole today at 20:00 UTC.

APOD: November 5, 1999 - Shadow Of Phobos
Explanation: Hurtling through space above the Red Planet, potato-shaped Phobos completes an orbit of Mars in less than eight hours. In fact, since its orbital period is shorter than the planet's rotation period, Mars-based observers see Phobos rise in the west and set in the east - traveling from horizon to horizon in about 5 1/2 hours. These three images from the Mars Global Surveyor (MGS) spacecraft record the oval shadow of Phobos racing over western Xanthe Terra on August 26, 1999. The area imaged is about 250 kilometers across and is seen in panels from left to right as red filter, blue filter, and combined color composite views from the MGS wide-angle camera system. The three dark spots most easily seen in the red image are likely small fields of dark sand dunes on crater floors. Standing in the shadow of Phobos, you would see the Martian version of a solar eclipse!

APOD: August 16, 1999 - Mars Weather Watch
Explanation: Mars may be a cold, dry planet but its weather is dynamic. On June 30, wide angle cameras on board the Mars Global Surveyor (MGS) spacecraft watched the development of this large scale storm system above Mars' north polar area. These frames were recorded on successive mapping orbits at intervals of about 2 hours, with the white north polar cap near the center of each. High winds seem to mix the brownish dust clouds and white water-ice clouds as the curling storm front churns over the extreme northern martain landscape. The MGS cameras have watched similar storms in this region during the months of July and August revealing surprisingly complex weather. Mars Climate Orbiter will join the MGS spacecraft in martian orbit in late September, and in December Mars Polar Lander is scheduled to touch down near the Red Planet's south pole.

APOD: August 9, 1999 - A Martian Dust Storm Approaches
Explanation: Batten down the hatches, here comes another Martian dust storm. The thin soil on Mars can be picked up by high winds to create dust storms that sweep down plains and can sometimes envelop most of the planet. The Mars Global Surveyor spacecraft currently orbiting Mars recently photographed such a dust storm raging on Mars' northern plains. The advancing storm front can be seen dividing clear and obscured areas on the photograph on the left. Even away from dust storms, isolated tornado like swirls called dust devils can reach 8-kilometers high and also be created by Martian winds. Studying wind phenomena on Mars provides valuable insight towards understand similar phenomena here on Earth.

APOD: July 23, 1999 - A Martian Valley
Explanation: This tantalizing close-up detail of a network of martian valleys was recorded from orbit this April by Mars Global Surveyor's camera. Water may once have flowed here but now sand dunes stripe the windswept valley floor. The Mars Global Surveyor spacecraft arrived in orbit in September of 1997 and has been exploring the red planet since. Three other spacecraft, Mars Climate Orbiter, Mars Polar Lander, and Nozomi are presently en route.

APOD: July 5, 1999 - Four Faces of Mars
Explanation: As Mars rotates, most of its surface becomes visible. During Earth's recent pass between Mars and the Sun, the Hubble Space Telescope was able to capture the most detailed time-lapse pictures ever from the Earth. Dark and light sand and gravel create an unusual blotted appearance for the red planet. Winds cause sand-tinted features on the Martian surface to shift over time. Visible in the above pictures are the north polar cap, made of water ice and dry ice, clouds including an unusual cyclone, and huge volcanoes leftover from ancient times. The Mars Global Surveyor satellite orbiting Mars continues to scan the surface for good places to land future robot explorers.

APOD: June 18, 1999 - Tharsis Volcanos
Explanation: Ice crystal clouds float above the immense Tharsis volcanos of Mars in this recently released picture from NASA's Mars Global Surveyor spacecraft. Olympus Mons at the upper left is 340 miles across and almost 15 miles high - the largest volcano in the solar system. In this sunny afternoon scene, the clouds are formed as warm martian air containing water vapour rises up the volcanic slopes. The water vapour cools and condenses into ice crystals. These reflective clouds are common in the Tharsis region, together creating a bright feature visible in earth-bound telescopes.

APOD: June 2, 1999 - Thermal Mars
Explanation: It's 2 AM on Mars and surface temperatures range from -65C to -120C, as measured by the Thermal Emission Spectrometer (TES) onboard the Mars Global Surveyor spacecraft. TES data used to make this detailed temperature map were acquired while passing over the night side of the Red Planet during 500 mapping orbits of Mars. With the warmest temperatures shown in white, progressing through red, yellow, and green colors to the coldest temperatures in blue, the map reveals the northern hemisphere during summer while the south experiences the cold martian winter. Near Mars' equator, the variations in nighttime temperatures are related to surface materials. Cold blue areas are covered with fine dust particles and the warmer regions are covered with coarser sand and rocks.

APOD: May 28, 1999 - Topographical Mars
Explanation: Contrasting colors trace changing elevations in this new high-resolution topographic map of Mars. Just released, the data were gathered in 1998 and 1999 by the Mars Orbiter Laser Altimeter (MOLA) onboard the Mars Global Surveyor spacecraft. The martian topography is seen to range over 19 miles between the highest volcanic peaks (white) and the lowest regions (purple). Along with the striking difference between the Red Planet's low northern hemisphere (top) and high southern regions, one of the most noticeable features on the map is the large blue-purple southern depression corresponding to the Hellas basin. Likely the result of an asteroid impact, Mars' deepest basin is about 1300 miles across making it one of the largest impact features in the Solar System. Explorations of MOLA's rich topographic database are expected to produce insights into water flows and the geologic history of Mars.

APOD: May 13, 1999 - Mars Volcano Apollinaris Patera
Explanation: Dwarfed by Olympus Mons and the other immense shield volcanos on Mars, Apollinaris Patera rises only 3 miles or so into the thin martian atmosphere, but bright water-ice clouds can be still be seen hovering around its summit. Mars' volcanic structures known as "paterae" are not only smaller than its shield volcanos but older as well, with ages estimated to be around 3 billion years. Like Apollinaris Patera, narrow furrows typically extend from their central craters or calderas. It is thought that the paterae represent broad piles of easily eroded volcanic ash. This wide angle view of Apollinaris Patera was recorded last month by the Mars Global Surveyor spacecraft. The large central crater is about 50 miles across.

APOD: May 4, 1999 - Magnetic Mars
Explanation: Mapping Mars from orbit, instruments on the Mars Global Surveyor (MGS) spacecraft have recently revealed banded magnetic field patterns - a startling and unanticipated suggestion that the Red Planet was more Earth-like in its distant past. The red and blue regions within the MGS orbital tracks across this portion of southern Mars indicate adjacent areas of crust where magnetic fields point in opposite directions. The bands seem to run east-west and are about 100 miles wide and 600 miles long. Such patterns are known to be produced on Earth by plate tectonics. As the crustal plates spread apart along the mid-ocean ridges, they carry a progressive banded record of Earth's changing magnetic field. The similar patterns on Mars are seen as evidence that it too once had moving crustal plates and a changing magnetic field, although both processes - still active on the larger planet Earth - are thought to have long since died away. These high resolution measurements of martian magnetism were made possible by the revised, close aerobraking orbits of the MGS spacecraft and not originally planned.

APOD: April 1, 1999 - Ski Mars
Explanation: These brightly reflecting fields of snow or frost are on the slopes of a crater rim in the northern hemisphere of Mars. They are 500 meters or so long and have lasted through about eight months of the Red Planet's spring and summer weather. Recently imaged by the Mars Global Surveyor spacecraft, they also seem to be relatively uncrowded ... suggesting to some on April 1st, that lift tickets on Mars are extremely expensive. Of course, a vacation on the Red Planet could still offer some advantages to skiing and snowboarding enthusiasts. For example, Mars' low gravity - only about 3/8ths Earth's gravity - would definitely tend to reduce sore muscles and fall-related injuries. Happy April Fools day from APOD.

APOD: March 19, 1999 - Mapping Mars
Explanation: This month, the Mars Global Surveyor (MGS) spacecraft began its primary mission to the red planet. Orbiting about once every two hours at an altitude of over 200 miles, instruments onboard MGS now regularly explore the Martian surface and atmosphere. This MGS polar mapping orbit was set up to achieve a favorable "afternoon" sun-angle for imaging as the spacecraft crosses over the day side of the planet. Mars' rotation will allow complete coverage of the surface roughly once every week with mapping operations planned for one Martian year (687 Earth days). These two opposite hemisphere views of Mars were pieced together from MGS wide-angle camera scans made in early March (blue and red lines mark the scan edges). Water-ice clouds can be seen hovering over the surface while the north polar cap is visible at the top of each image.

APOD: March 15, 1999 - Happy Face Crater on Mars
Explanation: Even Mars can put on a happy face. The Martian crater Galle has internal markings reminiscent of a smiley face symbol. Such markings were originally discovered in the late 1970s in pictures taken by the Viking Orbiter. A large meteor impacted the Martian surface to form the crater. Conventional wisdom holds that the markings inside the crater are placed by chance by natural processes. The Mars Global Surveyor (MGS) spacecraft currently orbiting Mars took the above picture. MGS recently started the global surveying phase of its mission.

APOD: December 16, 1998 - 3-D Mars North Pole
Explanation: This dramatic premier three-dimensional visualization of Mars' north pole is based on elevation measurements made by an orbiting laser. During the Spring and Summer of 1998 the Mars Orbiter Laser Altimeter (MOLA) flashed laser pulses toward the Martian surface from the Global Surveyor spacecraft and recorded the time it took to detect the reflection. This timing data has now been translated to a detailed topographic map of Mars' north polar terrain. The map indicates that the ice cap is is about 1,200 kilometers across, a maximum of 3 kilometers thick, and cut by canyons and troughs up to 1 kilometer deep. The measurements also indicate that the cap is composed primarily of water ice with a total volume of only about four percent of planet Earth's Antarctic ice sheet. In all it represents at most a tenth of the amount of water some scientists believe once existed on ancient Mars. Where did all the water go?

APOD: October 19, 1998 - Olympus Mons From Orbit
Explanation: Olympus Mons on Mars is the largest volcano in the Solar System. Although three times higher than Earth's Mount Everest, Olympus Mons would not be difficult to climb because of the volcano's great breadth. Covering an area greater than the entire Hawaiian volcano chain, the slopes of Olympus Mons typically rise only a few degrees at a time. The low gravity of Mars combined with a relatively static surface crust allow volcanoes this large to build up over time. This representative-color image was taken last April by the Mars Global Surveyor spacecraft currently orbiting Mars.

APOD: September 24, 1998 - The North Pole Of Mars
Explanation: The North Pole of Mars is capped by layers likely consisting of ice and dust deposited over millions of years. Imaged on September 12 - early Spring for Northern Mars - by the Mars Global Surveyor's camera, this synthesized wide-angle color view shows the rippled, eroded polar terrain covered with pinkish seasonal carbon dioxide frost. Dark areas bordering the polar cap are fields of sand dunes. This is the last picture scheduled to be taken by Surveyor's camera until it resumes operation in late March 1999. Over the past year of operation, the camera has taken about 2,000 pictures of Mars. Meanwhile, the spacecraft will begin its second round of aerobraking to achieve a circularized martian mapping orbit.

APOD: September 14, 1998 - Dust Hip Deep on Phobos
Explanation: Landing on the Martian Moon Phobos might be harder than previously thought. The reason: Moon dust. Recent photographs of Phobos have indicated that a layer of fine powder estimated to be a meter deep covers the whole surface. Evidence comes from infrared pictures that indicate the rapid speed that Phobos' surface cools after sunset. The above high-resolution picture of Phobos was taken last month by the Mars Global Surveyor spacecraft now orbiting Mars. The larger of two Martian moons, measures about 20 kilometers across, and orbits so close that Mars' gravity should rip it apart in another 50 million years.

APOD: August 14, 1998 - The Dunes Of Mars
Explanation: The North Pole of Mars is ringed by a "sea of sand dunes". For Mars' Northern Hemisphere, Spring began in mid July and increased sunlight is now shrinking the polar cap revealing the wind-swept dunes to the cameras onboard the Mars Global Surveyor spacecraft. North is up in this recently released close-up which covers a region about 1.2 miles across at 77 degrees Northern Martian Latitude. These dunes have been formed by winds generally blowing from the Southwest and are still covered with scattered white patches of carbon dioxide frost. Near the end of January 1999 Summer will begin and offer even clearer views of Northern dunes of Mars.

APOD: July 30, 1998 - Volcanos on Mars: Elysium Region
Explanation: This "synthetic color" image swath of the Elysium Volcanic Region of Mars was recorded by Mars Global Surveyor's wide angle camera on July 2. North is up and the sun illuminates the scene from the lower right. Bright clouds hover near the northern most dome-shaped volcano Hecates Tholus. The shield volcano Elysium Mons lies about 250 miles south near the image center, and farther south lies another dome-shaped volcano, Albor Tholus, with a broad summit basin or caldera. Even though Mars is just half the size of planet Earth, it is known for its volcanos - the largest of which dwarf their terrestrial counterparts.

APOD: June 19, 1998 - Good Morning Mars
Explanation: Looking down on the Northern Hemisphere of Mars on June 1, the Mars Global Surveyor spacecraft's wide angle camera recorded this morning image of the red planet. Mars Global Surveyor's orbit is now oriented to view the planet's surface during the morning hours and the night/day shadow boundary or terminator arcs across the left side of the picture. Two large volcanos, Olympus Mons (left of center) and Ascraeus Mons (lower right) peer upward through seasonal haze and water-ice clouds of the Northern Martian Winter. The color image was synthesized from red and blue band pictures and only approximates a "true color" picture of Mars.

APOD: June 8, 1998 - A Mars Glint
Explanation: If aligned just right, even a planet can produce a glint. The above combined pictures of Mars make the red planet appear unusually elongated - Mars is really almost spherical. However, these pictures were taken when the Sun was nearly directly behind the Mars Global Surveyor (MGS) spacecraft. This created a view for MGS where every part of Mars that was visible was also illuminated by the Sun. From this vantage point, though, sunlight reflects off the Martian surface and atmosphere producing a bright spot in the center - a glint. The brightness, color, and extent of the glint carry valuable information about the composition and physical properties of Mars.

APOD: June 3, 1998 - Martian Crater Shows Evidence of Dried Pond
Explanation: Did a pond once exist in this Martian crater? Recent photographs by the spacecraft Mars Global Surveyor, currently in orbit around Mars, show features unusual for Mars yet similar to a dried pond on Earth. Previously, much evidence suggested the effects of ancient channels of flowing water on Mars, but less evidence had been found for dried pools of water. Islands and bays on this crater floor indicate an accumulation of some liquid, however, a hypothesis consistent with channels found on the (inset) crater walls. As it is also possible the features were formed by other mechanisms including flowing lava, future observations and analysis will be needed to say for sure.

APOD: April 30, 1998 - Mars: Big Crater in Stereo
Explanation: Get out your red/blue glasses and check out this stereo picture of "Big Crater" on Mars! (Pieces of red and blue or green clear plastic will do. Your right eye should look through the red piece.) The stereo perspective was created by combining images from the Mars Global Surveyor spacecraft taken on two different orbits, each with a slightly different viewing angle. At just under a mile in diameter, Big Crater is not all that big but it is an important landmark in the vicinity of the Mars Pathfinder landing site on an ancient flood plain in Ares Vallis. Identifying corresponding smaller scale features in Pathfinder and Surveyor images will help to precisely locate the lander. Meanwhile, the line of sight between the Earth and Mars is approaching the Sun. During this period, known as solar conjunction, communicating with Mars Global Surveyor will be difficult.

APOD: April 17, 1998 - Mars: Looking For Viking
Explanation: On July 20, 1976, the Viking 1 lander touched down on the Martian Chryse Planitia. Its exact landing site is somewhere in the white rectangle above. Unfortunately, this wide angle Mars Global Surveyor image taken on April 12 reveals a substantial dust storm in the area with light colored plumes apparently blowing toward the upper right of the picture. Attempts to find the first spacecraft to land on Mars in the corresponding high resolution narrow field images have not been successful due in part to the increased atmospheric haze. The region shown here is about 100 miles across.

APOD: April 16, 1998 - Mars: Cydonia Close Up
Explanation: The Mars Global Surveyor spacecraft has returned another close-up of the Cydonia region on Mars. Orbiting over clear Martian skies at a range of about 200 miles, the Mars Orbiter Camera looked down on features known as the "City" on Mars and produced a high resolution image covering a swath around 1.5 by 15 miles at a pixel size of about 8.2 feet. This cropped portion of the processed image shows an area approximately 1.5 miles wide. Heavily weathered hills and pocked surfaces suggest the erosion of layers of the ancient Martian crust.

APOD: April 7, 1998 - Return To Cydonia
Explanation: Yesterday the Mars Global Surveyor project released a new close-up image of a portion of the Cydonia region on Mars. This cropped and processed version shows an area about 2 miles wide (the full version covers a strip nearly 2.6 miles wide by 25 miles long) and at full resolution has a pixel size of about 14 feet. The rock formation visible is the famous feature seen as the "Face on Mars" in 1976 Viking orbiter images. Such complex looking landforms in the Cydonia region are thought to be the result of erosion and weathering of ancient crust by Martian winds, frost, and possibly surface water. Mars Global Surveyor is scheduled to take other images of the Cydonia region and the Mars Pathfinder and Viking landing sites this month.

APOD: April 6, 1998 - A Face On Mars
Explanation: This image, showing what looks to be a human face (above center) and other features of the Cydonia region on the Martian surface, was produced using data from NASA's Viking 1 orbiter in 1976. Described in a NASA press release as a "rock formation which resembles a human head", some have since offered the extraordinary explanation that the face is an artificial construct built by a civilization on Mars! However, most scientists have a more conventional view - that this feature is indeed a natural Martian hill whose illusory face-like appearance depends on illumination and viewing angle. This month, the Mars Global Surveyor satellite will be in position to take new pictures of this region of controversial Martian features along with areas around the Mars Pathfinder and Viking landing sites.

APOD: March 20, 1998 - Mars: Ridges Near the South Pole
Explanation: No, it's not breakfast ... but looking down from an orbiting spacecraft, the odd intersecting ridges covering this area of Mars do present a waffle-like appearance. The cause of the ridge pattern is unknown but it suggests that more complex layered deposits lie below. The south polar region in this Mars Global Surveyor image measures about 8.5 by 12 miles and is spread with a layer of bright, seasonal carbon dioxide frost. Mysterious dark spots which pepper some of the interridge areas are 60 to 300 feet across. Their exact nature is also unknown, but these spots have apparently defrosted early and lack the bright layer of frozen carbon dioxide.

APOD: March 19, 1998 - Mars: A Canyon's Edge
Explanation: High resolution Mars Global Surveyor images were combined with Viking Orbiter color data to produce this stunning, detailed view of a Martian canyon's edge. The area pictured is about 6 miles wide and represents a tiny part of the northern edge of the canyon Valles Marineris, whose total length is about 2,500 miles. Details 20 to 30 feet across can be seen in the high resolution data. The composition of the thin, well-defined layers in the steep canyon walls is unknown, but their presence points to a complex and active Martian geologic history. In the later half of the 1970s, NASA's Viking Orbiters photographed Mars extensively, yet Surveyor's sharp new images have produced some striking and unanticipated results.

APOD: March 17, 1998 - Clouds Over Tharsis on Mars
Explanation: When and where do clouds form on Mars? The Mars Global Surveyor spacecraft currently orbiting Mars is finding out. Photographs released last week showed clouds forming above Tharsis, a huge bulge on Mars about 4000 kilometers across and 7 kilometers high containing several large volcanoes. These clouds temporarily disappeared as a large dust storm emerged from the South, the first developing dust storm to be tracked by an orbiting spacecraft. Mars Global Surveyor continues to aerobrake during on its ongoing mission to survey the planet Mars.

APOD: February 12, 1998 - In A Grand Canyon On Mars
Explanation: In a grand canyon on Mars, steep slopes fall away from a smooth plateau revealing striking layered rock formations. The canyon is part of the Valles Marineris, a 2,500 mile long system of canyons cutting across the Martian equator. This view, recorded on January 1 by the orbiting Mars Global Surveyor shows a small portion of Valles Marineris in amazing detail. The image is about 6 miles wide and high resolution versions show features as small as 20 feet across. What processes caused the layering? In the Grand Canyon on planet Earth, sedimentary processes have resulted in spectacular rock layers. But similar layers of rock in canyons of the Hawaiian Islands were created by volcanoes. Regardless of the origin of layering on Mars, its extent suggests that early Mars was geologically active and complex.

APOD: February 10, 1998 - All of Mars
Explanation: Mars Global Surveyor is photographing Mars. The robot spacecraft arrived last September and continues to use solar panel aerobraking to help maneuver it to a better orbit to survey all of Mars The above image is a reconstruction of several photographs digitally combined to simulate a single vantage point 2700 kilometers above the Martian surface. The images were taken by the Mars Orbital Camera in wide angle mode in late December 1997. Visible features include the Valles Marineris canyon across the top, and the South Polar Cap of frozen carbon dioxide at the bottom. Many finer features that would normally be visible are hidden by dust remaining from a planet-wide storm that subsided only three weeks before these images were recorded.

APOD: February 5, 1998 - A Martian River Bed
Explanation: This canyon on the surface of Mars appears to have been carved by flowing water. Known as Nanedi Vallis, the terraces and channels visible within the canyon strongly suggest that a river of water once ran here. But the lack of smaller surface channels and other features argue that the valley was formed by a surface collapse. Further images of Martian valley systems will help distinguish the degree to which these processes affected the Martian surface. This image was recorded on January 8th by the Mars Global Surveyor's camera during its 87th orbit of the red planet. The area pictured is about 6 miles wide. High resolution versions of the image show features that are as small as 40 feet across.

APOD: December 11, 1997 - A Martian Lake Bed
Explanation: Look closely. In this Mars Global Surveyor image of the Martian surface just south of Schiaparelli crater, dark lines appear to criss-cross light colored depressions. One tantalizing possibility is simply that the feature near the center is similar to a dried-up lake bed on planet Earth, where light colored mineral deposits are left as water evaporates and cracks are produced as the ground dries. This potential Martian lake bed is roughly 3/4 miles across and may provide further evidence that Mars once possessed surface water. Recently announced results from the Mars Pathfinder mission also point to a Martian past which included a denser atmosphere and surface water - conditions which could have supported life.

APOD: November 13, 1997 - Mars: A Sheer Close Up
Explanation: As the Mars Global Surveyor spacecraft maneuvers toward its final mapping orbit, its cameras have been producing some sharp views of Mars. At a resolution of better than 30 feet per pixel, this image of a portion of the immense canyon, Valles Marineris, highlights the sheer mountain cliffs over 3200 feet tall near the canyon walls. The striking and extensive layering clearly apparent in the triangular mountain face was totally unanticipated. This exciting new result challenges common theories about the surface of Mars and argues that a complex early geological history is responsible for the current Martian landscape.

APOD: October 31, 1997 - Haunting Mars
Explanation: This Halloween, the news about Mars is good news - Mars Global Surveyor will resume aerobraking into a mapping orbit around the haunting red planet. Wide angle cameras onboard the spacecraft recently recorded this shadowy image of Olympus Mons, the Solar System's largest volcano, from an altitude of over 100 miles. The summit depression or caldera of Olympus Mons is about 40 miles across and 15 miles above the Martian surface. On Halloween Night in 1938, Mars also made the news when Orson Welles' radio theatre adaptation of H.G. Wells' "War of the Worlds" - a fictional account of invaders from Mars - was dramatized as a live news report. The performance was so convincing it tricked some listeners, but most who heard the broadcast felt it was a treat. Have a happy and safe Halloween!

APOD: October 17, 1997 - Mars: A Mist In Mariner Valley
Explanation: An icy mist and late afternoon clouds cover much of this section of Valles Marineris on Mars. The Valles Marineris or Mariner Valley is a huge canyon system about 2,000 miles long and up to 5 miles deep. This test image was produced using data from Mars Global Surveyor's wide angle cameras viewing the canyon from a distance of 360-600 miles. Color was synthesized using images recorded through blue and red filters. Mission controllers have recently raised the spacecraft's aerobraking orbit to study the unexpected motion of one of the Surveyor's solar panels.

APOD: October 6, 1997 - Surveyor At Mars
Explanation: Mars Global Surveyor achieved Martian orbit on September 11 and began aerobraking into its final mapping orbit, a process that will take until March next year. Anticipating the labors ahead, Mars Orbital Camera operators have begun acquiring test images. This dramatic detail of a recent image shows a 10 mile wide swath of a highland valley, part of the Nirgal Vallis system. The original image was recorded from an altitude of 250 miles at a resolution of about 30 feet per pixel and has been rotated to represent the camera's perspective view. Were these valleys formed by flowing water or did collapse and erosion caused by ground water produced the channel? What other processes were important? Time will tell. From its planned mapping orbit, with four times better resolution, Mars Global Surveyor's images should provide answers to these and other questions about Mars.

APOD: September 23, 1997 - A Martian Autumn Begins
Explanation: Today is the first day of Autumn in the Northern Hemisphere of Planet Earth. The Autumnal Equinox occured yesterday at 7:56 pm EDT as the Sun crossed the celestial equator from North to South. Mars has seasons too and for the same reason that Earth does -- like Earth, Mars' axis of rotation is tilted with respect to the plane of its orbit around the sun. Eleven days ago Autumn also came to Mars' Northern Hemisphere and the Hubble Space Telescope recorded this image of the red planet to look for seasonal changes in the Martian weather. Clouds appear to cover the north polar regions while a dust storm rages in the south. The subject of weather on Mars is important to the just arrived Mars Global Surveyor spacecraft as it uses the innovative technique of aerobraking to establish a suitable mapping orbit around Mars.

APOD: September 15, 1997 - Olympus Mons on Mars: The Largest Volcano
Explanation: The largest volcano in the Solar System is on Mars. Olympus Mons rises 24 kilometers high and measures 550 km across. By comparison, Earth's largest volcano, Mauna Loa in Hawaii, rises 9 km high and measures 120 km across. Such large volcanoes can exist on Mars because of the low gravity and lack of surface tectonic motion. Olympus Mons is a shield volcano, built by fluid lava. Over the next three years, Mars Global Surveyor, which arrived at Mars last week, will photograph the planet at such high resolution that objects only 100 meters across will be visible. The above image was taken by Mariner 9, which orbited and photographed Mars during 1971 and 1972.

APOD: September 11, 1997 - Mars Global Surveyor: Aerobraking
Explanation: Completing a 10 month journey, another spacecraft from Earth arrives at Mars today. The Mars Global Surveyor (MGS) is scheduled to fire its main rocket engine for 22 minutes at 6:17 p.m. PDT and enter a highly elliptical orbit, with a low point 186 miles and a high point 34,800 miles above the surface of Mars. This robot spacecraft is aptly named. Its mission is to undertake a detailed planetwide survey of Mars. But first MGS must circularize its orbit, lowering the high point to about 250 miles. Instead of relying solely on its rocket engine, MGS mission controllers will use a fuel-saving technique known as aerobraking - dipping the spacecraft into the Martian atmosphere where it will encounter increased atmospheric drag. This early artist's conception emphasizes the drag created by the wing-like solar panels. The cumulative effect should find MGS in a more circular mapping orbit by March 1998. To successfully use aerobraking, mission controllers must achieve an exact orbit and will be handicapped by a limited knowledge of the thickness of the Martian atmosphere. They may even need to alter the spacecraft's course to compensate for changes in Martian weather.

APOD: August 16, 1997 - Pictured: An Ancient Martian
Explanation: Alien! Alien? Is this what an ancient Martian looked like? The tube-like form on the above highly magnified image is now believed by many to be a fossil of a simple Martian organism that lived over 3.6 billion years ago. If this extraordinary claim is true, this alien could hardly have been less intimidating as its fossil measures less than 1/100th the width of a human hair. A reconstruction of events indicates that the meteorite that housed this potential fossil was catapulted from Mars during a huge impact 16 million years ago and fell to Earth's Antarctica only 13,000 years ago. Evidence supporting this claim of early Martian life includes organic molecules and mineral features characteristic of biological activity found in the meteorite. NASA's current missions to Mars are Mars Global Surveyor and Mars Pathfinder. Though not designed to look for martian fossils, these missions may reveal information about conditions on early Mars which might have been more favorable for life.

APOD: May 22, 1997 - Bound For Mars
Explanation: Two NASA spacecraft, Mars Global Surveyor and Mars Pathfinder, are presently approaching the red planet. Pathfinder is scheduled to land on July 4th and Global Surveyor due to enter orbit in September. Recent studies of the Martian climate, motivated by this impending invasion of spacecraft from Earth, have indicate that Mars weather is more chaotic than previously thought - showing abrupt swings between "hot and dusty" and "cold and cloudy". These Hubble Space Telescope images from March 1997 show the Northern Hemisphere in early Martian summer, with a receding polar cap and whitish water-ice clouds. The left image is centered on Ares Valles, Pathfinder's landing site, while in the right image, towering Tharsis mountains (massive extinct volcanoes) can be seen poking through the clouds. Stretching to the eastern edge of the righthand image (at lower right) is the Valles Marineris, an immense canyon system. Martian weather reports will play an important role in mission planning. Both spacecraft rely on the Martian atmosphere for braking maneuvers and Pathfinder's lander and rover are solar powered.

APOD: March 24, 1997 - The Weather on Mars
Explanation: Would Mars be a nice place to visit? Sometimes. Much of Mars undergoes severe changes in climate during its orbit around the Sun, ranging from extreme cold to temperatures enjoyable by humans. But Mars is usually a nice place to visit for hardy spacecraft, and in fact the Mars Pathfinder and Mars Global Surveyor missions are currently headed for the "Red Planet." In preparation for the scheduled Mars Pathfinder landing on July 4^th, 1997, the Earth-Orbiting Hubble Space Telescope recently took the above high resolution photograph. The picture shows the onset of Martian summer (northern hemisphere) when, apparently, the northern polar cap recedes to uncover dark sand dunes.

APOD: August 8, 1996 - Pictured: An Ancient Martian?
Explanation: Alien! Alien? Is this what an ancient Martian looked like? The tube-like form on the above highly magnified image is now believed by many to be a fossil of a simple Martian organism that lived over 3.6 billion years ago. If this extraordinary claim is true, this alien could hardly have been less intimidating as its fossil measures less than 1/100th the width of a human hair. A reconstruction of events indicates that the meteorite that housed this potential fossil was catapulted from Mars during a huge impact 16 million years ago and fell to Earth's Antarctica only 13,000 years ago. Evidence supporting this claim of early Martian life includes organic molecules and mineral features characteristic of biological activity found in the meteorite. NASA missions to Mars in the next few years include Mars Global Surveyor and Mars Pathfinder, which may uncover data that help confirm or refute this exciting claim.

APOD: July 20, 1996 - 20 Years Ago: Vikings on Mars
Explanation: On July 20, 1976, NASA's Viking 1 lander become the first spacecraft to land on Mars, followed weeks later by its twin robot explorer, the Viking 2 lander. Operating on the Martian surface into the early 1980s, the Vikings took thousands of pictures, conducted sophisticated chemical searches for life and studied the Martian weather and geology. In the dramatically detailed image above, a field of rocks and boulders is viewed from the Viking 1 landing sight on Chryse Planitia (the Plain of Chryse). Viking 1's dusty foot pad is just visible at the lower right. The image was created by combining high resolution black and white images with lower resolution color images of the same area. NASA is planning to continue its extremely productive and well chronicled exploration of the mysterious Red Planet with the Mars Global Surveyor and the Mars Pathfinder missions. What's Mars like today?