Astronomy Picture of the Day Search Results for "Mars Express"

APOD: 2024 September 9 – Mars: Moon, Craters, and Volcanos
Explanation: If you could fly over Mars, what might you see? The featured image shows exactly this in the form of a Mars Express vista captured over a particularly interesting region on Mars in July. The picture's most famous feature is Olympus Mons, the largest volcano in the Solar System, visible on the upper right. Another large Martian volcano is visible on the right horizon: Pavonis Mons. Several circular impact craters can be seen on the surface of the aptly named red planet. Impressively, this image was timed to capture the dark and doomed Martian moon Phobos, visible just left of center. The surface feature on the lower left, known as Orcus Patera, is unusual for its large size and oblong shape, and mysterious because the processes that created it still remain unknown. ESA's robotic Mars Express spacecraft was launched in 2003 and, among many notable science discoveries, bolstered evidence that Mars was once home to large bodies of water.

APOD: 2024 February 26 – Martian Moon Eclipses Martian Moon
Explanation: What if there were two moons in the sky -- and they eclipsed each other? This happens on Mars. The featured video shows a version of this unusual eclipse from space. Pictured are the two moons of Mars: the larger Phobos, which orbits closer to the red planet, and the smaller Deimos, which orbits further out. The sequence was captured last year by the ESA’s Mars Express, a robotic spacecraft that itself orbits Mars. A similar eclipse is visible from the Martian surface, although very rarely. From the surface, though, the closer moon Phobos would appear to pass in front of farther moon Deimos. Most oddly, Phobos orbits Mars so close that it appears to move backwards when compared to Earth's Moon from Earth, rising in west and setting in the east. Phobos, the closer moon, orbits so close and so fast that it passes nearly overhead about three times a day.

APOD: 2023 July 31 – Phobos over Mars
Explanation: Why is Phobos so dark? Phobos, the largest and innermost of the 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 featured assigned-color picture of Phobos near the edge of Mars was captured in late 2021 by ESA's robot spacecraft Mars Express, currently orbiting Mars. Phobos is a heavily cratered and barren moon, with its largest crater located on the far side. From 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, while 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: 2023 April 4 – Olympus Mons: Largest Volcano in the Solar System
Explanation: The largest volcano in our Solar System is on Mars. Although three times higher than Earth's Mount Everest, Olympus Mons will not be difficult for humans to climb because of the volcano's shallow slopes and Mars' low gravity. Covering an area greater than the entire Hawaiian volcano chain, the slopes of Olympus Mons typically rise only a few degrees at a time. Olympus Mons is an immense shield volcano, built long ago by fluid lava. A relatively static surface crust allowed it to build up over time. Its last eruption is thought to have been about 25 million years ago. The featured image was taken by the European Space Agency's robotic Mars Express spacecraft currently orbiting the Red Planet.

APOD: 2022 August 6 - Stereo Phobos
Explanation: Get out your red/blue glasses and float next to Phobos, grooved moon of Mars! Captured in 2004 by the High Resolution Stereo Camera on board ESA's Mars Express spacecraft, the image data was recorded at a distance of about 200 kilometers from the martian moon. This tantalizing stereo anaglyph view shows the Mars-facing side of Phobos. It highlights the asteroid-like moon's cratered and grooved surface. Up to hundreds of meters wide, the mysterious grooves may be related to the impact that created Stickney crater, the large crater at the left. Stickney crater is about 10 kilometers across, while Phobos itself is only around 27 kilometers across at its widest point.

APOD: 2020 November 8 - Martian Moon Phobos from Mars Express
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 featured picture of Phobos near the limb of Mars was captured in 2010 by the robot spacecraft Mars Express currently orbiting Mars. Phobos is a heavily cratered and barren moon, with its largest crater located on the far side. From 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: 2019 April 22 - Mars Methane Mystery Deepens
Explanation: The methane mystery on Mars just got stranger. New results from ESA and Roscosmos' ExoMars Trace Gas Orbiter, has unexpectedly not detected methane in the atmosphere of Mars. This result follows the 2013 detection of methane by NASA's Curiosity rover, a result seemingly confirmed by ESA's orbiting Mars Express the next day. The issue is so interesting because life is a major producer of methane on Earth, leading to intriguing speculation that some sort of life -- possibly microbial life -- is creating methane beneath the surface of Mars. Non-biological sources of methane are also possible. Pictured is a visualization of the first claimed methane plume over Mars as detected from Earth in 2003. The new non-detection of methane by the ExoMars Orbiter could mean that Mars has some unexpected way of destroying methane, or that only some parts of Mars release methane -- and possibly only at certain times. As the mystery has now deepened, humanity's scrutiny of our neighboring planet's atmosphere will deepen as well.

APOD: 2018 July 31 - Layers of the South Pole of Mars
Explanation: What lies beneath the layered south pole of Mars? A recent measurement with ground-penetrating radar from ESA's Mars Express satellite has detected a bright reflection layer consistent with an underground lake of salty water. The reflection comes from about 1.5 kilometers down and covers an area 20 kilometers across. Liquid water evaporates quickly from the surface of Mars, but a briny confined lake, such as implied by the radar reflection, could last much longer and be a candidate to host life such as microbes. Pictured, an infrared, green, and blue image of the south pole of Mars taken by Mars Express in 2012 shows a complex mixture of layers of dirt, frozen carbon dioxide, and frozen water.

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: 2017 May 28 - Collapse in Hebes Chasma on Mars
Explanation: What's happened in Hebes Chasma on Mars? Hebes Chasma is a depression just north of the enormous Valles Marineris canyon. Since the depression is unconnected to other surface features, it is unclear where the internal material went. Inside Hebes Chasma is Hebes Mensa, a 5 kilometer high mesa that appears to have undergone an unusual partial collapse -- a collapse that might be providing clues. The featured image, taken by ESA's robotic Mars Express spacecraft currently orbiting Mars, shows great details of the chasm and the unusual horseshoe shaped indentation in the central mesa. Material from the mesa appears to have flowed onto the floor of the chasm, while a possible dark layer appears to have pooled like ink on a downslope landing. A recent hypothesis holds that salty rock composes some lower layers in Hebes Chasma, with the salt dissolving in melted ice flows that drained through holes into an underground aquifer.

APOD: 2016 July 23 - Summer Planets and Milky Way
Explanation: Lights sprawl toward the horizon in this night skyscape from Uludag National Park, Bursa Province, Turkey, planet Earth. The stars and nebulae of the Milky Way are still visible though, stretching above the lights on the northern summer night while three other planets shine brightly. Jupiter is at the far right, Mars near the center of the frame, and Saturn is just right of the bulging center of our galaxy. Because the panoramic scene was captured on July 6, all three planets pictured were hosting orbiting, operational, robotic spacecraft from Earth. Popular Mars has five (from three different space agencies): MAVEN (NASA), Mars Orbiter Mission (India), Mars Express (ESA), Mars Odyssey (NASA), Mars Reconnaissance Orbiter (NASA). Ringed Saturn hosts the daring Cassini spacecraft. Just arrived, Juno now orbits ruling gas giant Jupiter.

APOD: 2014 October 20 - Comet Siding Spring Passes Mars
Explanation: Yesterday, a comet passed very close to Mars. In fact, Comet C/2013 A1 (Siding Spring) passed closer to the red planet than any comet has ever passed to Earth in recorded history. To take advantage of this unique opportunity to study the close interaction of a comet and a planet, humanity currently has five active spacecraft orbiting Mars: NASA's MAVEN, MRO, Mars Odyssey, as well as ESA's Mars Express, and India's Mars Orbiter. Most of these spacecraft have now sent back information that they have not been damaged by small pieces of the passing comet. These spacecraft, as well as the two active rovers on the Martian surface -- NASA's Opportunity and Curiosity -- have taken data and images that will be downloaded to Earth for weeks to come and likely studied for years to come. The featured image taken yesterday, however, was not taken from Mars but from Earth and shows Comet Siding Spring on the lower left as it passed Mars, on the upper right.

APOD: 2014 August 12 - Collapse in Hebes Chasma on Mars
Explanation: What's happened in Hebes Chasma on Mars? Hebes Chasma is a depression just north of the enormous Valles Marineris canyon. Since the depression is unconnected to other surface features, it is unclear where the internal material went. Inside Hebes Chasma is Hebes Mensa, a 5 kilometer high mesa that appears to have undergone an unusual partial collapse -- a collapse that might be providing clues. The above image, taken by the robotic Mars Express spacecraft currently orbiting Mars, shows great details of the chasm and the unusual horseshoe shaped indentation in the central mesa. Material from the mesa appears to have flowed onto the floor of the chasm, while a possible dark layer appears to have pooled like ink on a downslope landing. A recent hypothesis holds that salty rock composes some lower layers in Hebes Chasma, with the salt dissolving in melted ice flows that drained through holes into an underground aquifer.

APOD: 2013 December 25 - Phobos 360
Explanation: What does the Martian moon Phobos look like? To better visualize this unusual object, images from ESA's Mars Express orbiter have been combined into a virtual rotation movie. The rotation is actually a digital illusion -- tidally-locked Phobos always keeps the same face toward its home planet, as does Earth's moon. The above video highlights Phobos' chunky shape and an unusually dark surface covered with craters and grooves. What lies beneath the surface is a topic of research since the moon is not dense enough to be filled with solid rock. Phobos is losing about of centimeter of altitude a year and is expected to break up and crash onto Mars within the next 50 million years. To better understand this unusual world, Mars Express is on course to make the closest flyby ever on Sunday.

APOD: 2011 August 8 - Seasonal Dark Streaks on Mars
Explanation: What is causing these dark streaks on Mars? A leading hypothesis is flowing -- but quickly evaporating -- water. The streaks, visible in dark brown near the image center, appear in the Martian spring and summer but fade in the winter months, only to reappear again the next summer. These are not the first markings on Mars that have been interpreted as showing the effects of running water, but they are the first to add the clue of a seasonal dependence. The above picture, taken in May, digitally combines several images from the the HiRISE instrument on the Mars Reconnaissance Orbiter (MRO). The image is color-enhanced and depicts a slope inside Newton crater in a mid-southern region of Mars. The streaks bolster evidence that water exists just below the Martian surface in several locations, and therefore fuels speculation that Mars might harbor some sort of water-dependent life. Future observations with robotic spacecraft orbiting Mars, such as MRO, Mars Express, and Mars Odyssey will continue to monitor the situation and possibly confirm -- or refute -- the exciting flowing water hypothesis.

APOD: 2011 August 1 - Shuttle Reentry Streak from Orbit
Explanation: What's that strange bright streak? It is the last image ever of a space shuttle from orbit. A week and a half ago, after decoupling from the International Space Station, the Space Shuttle Atlantis fired its rockets for the last time, lost its orbital speed, and plummeted back to Earth. Within the next hour, however, the sophisticated space machine dropped its landing gear and did what used to be unprecedented -- landed like an airplane on a runway. Although the future of human space flight from the USA will enter a temporary lull, many robotic spacecraft continue to explore our Solar System and peer into our universe, including Cassini, Chandra, Chang'e 2, Dawn, Fermi, Hubble, Kepler, LRO, Mars Express, Messenger, MRO, New Horizons, Opportunity, Planck, Rosetta, SDO, SOHO, Spitzer, STEREO, Swift, Venus-Express, and WISE.

APOD: 2011 January 24 - Phobos South Pole from Mars Express
Explanation: Where on this moon would you land? The moon pictured above is not Earth's moon but Phobos, the closest moon to the planet Mars. Phobos is so close to Mars that it is expected to break up and crash into the red planet within the next 100 million years. Earlier just this year, however, ESA's Mars Express mission took detailed images of the area surrounding Phobos' South Pole. Visible on the small moon's unusually dark surface are many circular craters, long chains of craters, and strange streaks. Large Stickney Crater, which looms on the far right, was also visible in the corresponding North Polar image taken last year. This and other similar images of Phobos are so detailed, resolving items even 10-meters across, that they are useful for examining proposed landing sites of the future Phobos-Grunt mission. The Russian Phobos-Grunt robotic spacecraft is scheduled to launch toward Phobos later this year and return surface samples in 2014.

APOD: 2010 December 1 - Martian Moon Phobos from Mars Express
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 of Phobos near the limb of Mars was captured last month by the robot spacecraft Mars Express currently orbiting Mars. Phobos is a heavily cratered and barren moon, with its largest crater located on the far side. From 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: 2010 March 17 - Phobos from Mars Express
Explanation: Why is this small object orbiting Mars? The origin of Phobos, the larger of the two moons orbiting Mars, remains unknown. Phobos and Deimos appear very similar to C-type asteroids, yet gravitationally capturing such asteroids, circularizing their orbits, and dragging them into Mars' equatorial plane seems unlikely. Pictured above is Phobos as it appeared during last week's flyby of ESA's Mars Express, a robotic spacecraft that began orbiting Mars in 2003. Visible in great detail is Phobos' irregular shape, strangely dark terrain, numerous unusual grooves, and a spectacular chain of craters crossing the image center. Phobos spans only about 25 kilometers in length and does not have enough gravity to compress it into a ball. Phobos orbits so close to Mars that sometime in the next 20 million years, tidal deceleration will break up the rubble moon into a ring whose pieces will slowly spiral down and crash onto the red planet. The Russian mission Phobos-Grunt is scheduled to launch and land on Phobos next year.

APOD: 2008 July 23 - High Cliffs Surrounding Echus Chasma on Mars
Explanation: What created this great cliff on Mars? Did giant waterfalls once plummet through its grooves? With a four-kilometer drop, this high cliff surrounding Echus Chasma, near an impressive impact crater, was carved by either water or lava. A leading hypothesis is that Echus Chasma, at 100-kilometers long and 10-kilometers wide, was once one of the largest water sources on Mars. If true, water once held in Echus Chasma likely ran over the Martian surface to carve the impressive Kasei Valles, which extends over 3,000 kilometers to the north. Even if initially carved by water, lava appears to have later flowed in the valley, leaving an extraordinarily smooth floor. Echus Chasma lies north of tremendous Valles Marineris, the largest canyon in the Solar System. The above image was taken by the robotic Mars Express spacecraft currently orbiting Mars.

APOD: 2008 April 7 - Mysterious White Rock Fingers on Mars
Explanation: What caused this unusual white rock formation on Mars? Intrigued by the possibility that they could be salt deposits left over as an ancient lakebed dried-up, detailed studies of these fingers now indicate that this is not correct. The light material appears to have eroded away from the surrounding area, indicating a very low-density composition, possibly consistent with volcanic ash or windblown dust. The stark contrast between the rocks and the surrounding sand is compounded by the sand's unusual darkness. This picture was taken from the Mars Express spacecraft currently orbiting Mars. Planetary scientist Emily Lakdawalla, among others, has followed her curiosity about this unusual Martian landform into a fascinating investigation that is eloquently described in the Planetary Society Weblog. The mysterious white rock spans about 15 kilometers across inside a larger crater that spans about 100 kilometers.

APOD: 2007 July 1 - Steep Cliffs on Mars
Explanation: Vertical cliffs of nearly two kilometers occur near the North Pole of Mars. Also visible in the above image of the Martian North Polar Cap are red areas of rock and sand, white areas of ice, and dark areas of unknown composition but hypothesized to be volcanic ash. The cliffs are thought to border volcanic caldera. Although the sheer drop of the Martian cliffs is extreme, the drop is not as deep as other areas in our Solar System, including the 3.4-kilometer depth of Colca Canyon on Earth and the 20 kilometer depth of Verona Rupes on Uranus' moon Miranda. The above image, digitally reconstructed into a perspective view, was taken by the High Resolution Stereo Camera on board the ESA's robotic Mars Express spacecraft currently orbiting Mars.

APOD: 2006 December 3 - Phobos: Doomed Moon of Mars
Explanation: This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. The larger moon, Phobos, is indeed seen to be a cratered, asteroid-like object in this stunning color image from the Mars Express spacecraft, recorded at a resolution of about seven meters per pixel. But Phobos orbits so close to Mars - about 5,800 kilometers above the surface compared to 400,000 kilometers for our Moon - that gravitational tidal forces are dragging it down. In 100 million years or so it will likely crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.

APOD: 2006 September 26- Mars Express: Return to Cydonia
Explanation: The unusual stone mesas of the Cydonia region on Mars are quite striking in appearance. Last week, the Mars Express project released a new close-up image of a portion of the Cydonia region on Mars. This new image, taken by the robotic Mars Express spacecraft now orbiting Mars, shows an area about 90 kilometers wide. In the far lower right of the above image, a particularly picturesque mesa can be seen as the upper right of the two mesas visible there. This mesa, when lit from just the right sun angle, can appear similar to a human face and became famous as the Face on Mars in 1976 Viking orbiter images. Better images show it to be just an interesting mesa. Such complex looking landforms in the Cydonia region are thought to be the result of landslides and erosion of the ancient Martian crust.

APOD: 2006 September 25 - Mars Express Close Up of the Face on Mars
Explanation: Wouldn't it be fun if clouds were turtles? Wouldn't it be fun if the laundry on the bedroom chair was a friendly monster? Wouldn't it be fun if rock mesas on Mars were faces or interplanetary monuments? Clouds, though, are small water droplets, floating on air. Laundry is cotton, wool, or plastic, woven into garments. Famous Martian rock mesas known by names like the Face on Mars appear quite natural when seen more clearly, as the above recently-released digital-perspective image shows. Is reality boring?

APOD: 2005 July 20 - Water Ice in a Maritan Crater
Explanation: What lies on the floor of this Martian crater? A frozen patch of water ice. The robotic Mars Express spacecraft took the above image in early February. The ice pocket was found in a 35-kilometer wide crater that resides 70 degrees north of the Martian equator. There, sunlight is blocked by the 300-meter tall crater wall from vaporizing the water-ice on the crater floor into the thin Martian atmosphere. The ice pocket may be as deep as 200 meters thick. Frost can be seen around the inner edge on the upper right part of the crater, while part of the lower left crater wall is bathed in sunlight. The existence of water-ice pockets inside craters near the Martian North Pole, like that pictured above and others noted previously, give clues not only about surface conditions in the Martian past but also possible places where future water-based astronauts might do well to land.

APOD: 2005 March 15 - Steep Cliffs on Mars
Explanation: Vertical cliffs of nearly two kilometers occur near the North Pole of Mars. Also visible in the above image of the Martian North Polar Cap are red areas of rock and sand, white areas of ice, and dark areas of unknown composition but hypothesized to be volcanic ash. The cliffs are thought to border volcanic caldera. Although the sheer drop of the Martian cliffs is extreme, the drop is not as deep as other areas in our Solar System, including the 3.4-kilometer depth of Colca Canyon on Earth and the 20 kilometer depth of Verona Rupes on Uranus' moon Miranda. The above image, digitally reconstructed into a perspective view, was taken by the High Resolution Stereo Camera on board the ESA's robotic Mars Express spacecraft currently orbiting Mars.

APOD: 2005 February 28 - Unusual Plates on Mars
Explanation: What are those unusual plates on Mars? A leading current interpretation holds that they are blocks of ice floating on a recently frozen sea covered by dust. The unusual plates were photographed recently by the European Space Agency's Mars Express spacecraft currently orbiting Mars. Oddly, the region lies near the Martian equator and not near either of Mars' frozen polar caps. Without being covered by dust, any water or ice near away from the poles would quickly evaporate right into the atmosphere. Evidence that the above-imaged plates really are dust-covered water-ice includes a similarity in appearance to ice blocks off Earth's Antarctica, nearby surface fractures from which underground water could have flowed, and the shallow depth of the craters indicating that something is filling them in. If correct, the low abundance of craters indicates that water may have flowed on Mars as recently as five million years ago.

APOD: 2005 February 17 - Melas, Candor, and Ophir: Valleys of Mariner
Explanation: First imaged by the Mariner 9 spacecraft, Valles Marineris, the grand canyon of Mars, is a system of enormous depressions or chasmas that stretch some 4,000 kilometers along the Martian equator. Looking north over the canyon's central regions, dark Melas Chasma lies in the foreground of this spectacular perspective view. Behind it are Candor Chasma and the steep walls of Ophir Chasma near the horizon. Faulting, surface collapse and landslides are seen to be part of the complex geologic history of these dramatic features, with layered deposits also found within the canyon system. Recorded in 2004, the image represents data from the High Resolution Stereo Camera (HRSC) on board ESA's Mars Express spacecraft. Melas, Candor and Ophir are about 200 kilometers wide and 5 to 7 kilometers deep.

APOD: 2004 November 20 - Stereo Phobos
Explanation: Get out your red/blue glasses and float next to Phobos, grooved moon of Mars! Also featured in yesterday's episode, the image data from the Mars Express High Resolution Stereo Camera was recorded at a distance of about 200 kilometers. This tantalizing stereo anaglyph view shows the Mars-facing side of the asteroid-like moon's cratered and grooved surface. Up to hundreds of meters wide, the mysterious grooves may be fractures related to the impact which created 10 kilometer wide Stickney crater, the large crater at the left.

APOD: 2004 November 19 - Phobos: Doomed Moon of Mars
Explanation: This moon is doomed. Mars, the red planet named for the Roman god of war, has two tiny moons, Phobos and Deimos, whose names are derived from the Greek for Fear and Panic. These martian moons may well be captured asteroids originating in the main asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. The largest moon, Phobos, is indeed seen to be a cratered, asteroid-like object in this stunning new color image from the Mars Express spacecraft, recorded at a resolution of about seven meters per pixel. But Phobos orbits so close to Mars - about 5,800 kilometers above the surface compared to 400,000 kilometers for our Moon - that gravitational tidal forces are dragging it down. In 100 million years or so it will likely crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.

APOD: 2004 September 30 - Crater Wall on Solis Planum
Explanation: This dramatic perspective view looks south-east along the wall of a large eroded impact crater on Solis Planum, bordering the mountainous Thaumasia region of Mars. Stretching for about 50 kilometers into the scene, the crater wall is around 800 meters high. Located just south and west of the Red Planet's grand Valles Marineris, this area features mountains and fault lines that are seen as evidence of surface plate motions or plate tectonics. The process of plate tectonics has long been shaping the surface of planet Earth but is thought to have been only briefly active on Mars. The image was constructed using color image data from the High Resolution Stereo Camera onboard ESA's Mars Express spacecraft.

APOD: 2004 July 29 - Melas Chasma
Explanation: Steep cliffs drop into the rugged terrain of Melas Chasma in this stunning view from the Mars Express spacecraft orbiting the Red Planet. At a scale of 16 meters per pixel, the image data from the orbiter's High Resolution Stereo Camera offers evidence that volcanic activity, water, wind erosion and marsquakes may all have shaped the region. Melas Chasma lies along the central southern edge of the large Valles Marineris, the grand canyon of Mars. While the Valles Marineris is itself over 4,000 kilometers long and up to 10 kilometers deep, the region pictured spans about 70 kilometers. The floor of Melas Chasma seen here is several kilometers below the surrounding plateau.

APOD: 2004 May 26 - At the Summit of Olympus Mons
Explanation: From martian orbit, the Mars Express cameras looked down on the largest volcano in the solar system. The result was this stunningly detailed overhead view of the caldera or summit crater region of Olympus Mons. Fittingly named for the lofty abode of the gods of Greek mythology, Olympus Mons rises 21 kilometers above the surrounding plain or to about 3 times the height of Mt. Everest. The area pictured is 102 kilometers across and the caldera pits are up to 3 kilometers deep. For comparison, hawaiian volcanic calderas range up to 18 kilometers in diameter. Outlined by steep cliffs, Olympus Mons itself is about 600 kilometers in diameter.

APOD: 2004 January 29 - Valles Marineris Perspective from Mars Express
Explanation: Europe's Mars Express satellite has started returning detailed color images of the red planet. The first of the current armada to arrive at Mars, the orbiting satellite will photograph the entire Martian surface to a resolution of 10 meters or higher, map the mineral composition to 100 meter resolution, and investigate the global circulation of the atmosphere. Pictured above is a 3D perspective of the first image released from this satellite -- a stunning computer reconstruction of part of the Valles Marineris region, a canyon nicknamed the Grand Canyon of Mars. In reality, Valles Marineris is four times longer and five times deeper than its Arizona counterpart. The above image shows a portion of Valles Marineris roughly 65 kilometers across, detailing many ridges and valleys. Mars Express is scheduled to continue to send back images for at least a full Martian year.

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: 2003 December 18 - Express to Mars
Explanation: Hurtling toward its destination, the high resolution camera on board ESA's Mars Express spacecraft recorded this tantalizing view of the Red Planet earlier this month on December 3rd. Seen from a distance of 5.5 million kilometers, features across part of Mars' western hemisphere are bathed in sunlight. The Martian night side is also prominent from the spacecraft's perspective, a view not possible for Earthbound telescopes. Launched on an interplanetary voyage of exploration in early June, Mars Express carries with it the Beagle 2 lander, scheduled to be released from Mars Express tomorrow, December 19th. Mars Express and Beagle 2 will then continue the journey separately, but both are scheduled to reach Mars on December 25th, with Mars Express entering an elliptical orbit and Beagle 2 descending to the Martian surface. Two more invaders from Earth, NASA's Mars Exploration Rovers, will arrive in January.

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 May 2 - Five to Mars
Explanation: Come December 2003 - January 2004, an armada of five new invaders from Earth should arrive on the shores of the Red Planet -- the Japanese ( ISAS) Nozomi orbiter, the European Space Agency's Mars Express orbiter carrying the Beagle 2 lander, and NASA's own two Mars Exploration Rovers. While Nozomi began its interplanetary voyage in 1998, the other spacecraft are scheduled for launch windows beginning this June. Clearly, earthdwellers remain intensely curious about Mars and the tantalizing possibility of past or present martian life, with these robotic missions focussing on investigating the planet's atmosphere and the search for water. This mosaic of over 100 Viking 1 orbiter images of Mars was recorded in 1980 and is projected to show the perspective seen from an approaching spacecraft at a distance of 2,000 kilometers. Exceptional views of Mars will be possible from earthbound telescopes in August and September.