Astronomy Picture of the Day Search Results for "Viking AND Mars"

APOD: 2021 July 4 - The Face on Mars
Explanation: Wouldn't it be fun if clouds were castles? Wouldn't it be fun if the laundry on the bedroom chair was a superhero? Wouldn't it be fun if rock mesas on Mars were interplanetary monuments to the human face? Clouds, though, are floating droplets of water and ice. 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 on better images. Is reality boring? Nobody knows why some clouds make rain. Nobody knows if life ever developed on Mars. Nobody knows why the laundry on the bedroom chair smells like root beer. Scientific exploration can not only resolve mysteries, but uncover new knowledge, greater mysteries, and yet deeper questions. As humanity explores our universe, perhaps fun -- through discovery -- is just beginning.

APOD: 2021 May 21 - Utopia on Mars
Explanation: Expansive Utopia Planitia on Mars is strewn with rocks and boulders in this 1976 image. Constructed from the Viking 2 lander's color and black and white image data, the scene approximates the appearance of the high northern martian plain to the human eye. For scale, the prominent rounded rock near center is about 20 centimeters (just under 8 inches) across. Farther back on the right side of the frame the a dark angular boulder spans about 1.5 meters (5 feet). Also in view are two trenches dug by the lander's sampler arm, the ejected protective shroud that covered the soil collector head, and one of the lander's dust covered footpads at the lower right. On May 14, China’s Zhurong Mars rover successfully touchdown on Mars and has returned the first images of` its landing site in Utopia Planitia.

APOD: 2020 May 24 - Valles Marineris: The Grand Canyon of Mars
Explanation: The largest canyon in the Solar System cuts a wide swath across the face of Mars. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Several geologic processes have been identified in the canyon. The featured mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s.

APOD: 2019 January 21 - InSight Lander Takes Selfie on Mars
Explanation: This is what NASA's Insight lander looks like on Mars. With its solar panels, InSight is about the size of a small bus. Insight successfully landed on Mars in November with a main objective to detect seismic activity. The featured selfie is a compilation of several images taken of different parts of the InSight lander, by the lander's arm, at different times. SEIS, the orange-domed seismometer seen near the image center last month, has now been placed on the Martian surface. With this selfie, Mars InSight continues a long tradition of robotic spacecraft on Mars taking and returning images of themselves, including Viking, Sojourner, Pathfinder, Spirit, Opportunity, Phoenix, and Curiosity. Data taken by Mars Insight is expected to give humanity unprecedented data involving the interior of Mars, a region thought to harbor formation clues not only about Mars, but Earth.

APOD: 2018 November 25 - 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. The origin of the Martian moons is unknown, though, with a leading hypothesis holding that they are captured asteroids. The larger moon, at 25-kilometers across, is Phobos, and is indeed seen to be a cratered, asteroid-like object in this false-colored image mosaic taken by the robotic Viking 1 mission in 1978. A recent analysis of the unusual long grooves seen on Phobos indicates that they may result from boulders rolling away from the giant impact that created the crater on the upper left: Stickney Crater. 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. The ultimate result will be for Phobos to break up in orbit and then crash down onto the Martian surface in about 50 million years. Well before that -- tomorrow, in fact, if everything goes according to plan -- NASA's robotic InSight lander will touch down on Mars and begin investigating its internal structure.

APOD: 2016 July 20 - Dark Dunes on Mars
Explanation: How does wind affect sand on Mars? To help find out if it differs significantly from Earth, the robotic Curiosity rover on Mars was directed to investigate the dark Namib Dune in the Bagnold Dune Field in Gale Crater. Namib is the first active sand dune investigated up close outside of planet Earth. Wind-created ripples on Earth-bound sand dunes appear similar to ripples on Mars, with one exception. The larger peaks visible on dark Namib dune, averaging about 3 meters apart, are of a type seen only underwater on Earth. They appear to arise on Mars because of the way the thin Martian wind drags dark sand particles. The featured image was taken last December and is horizontally compressed to show context. In the distance, a normal dusty Martian landscape slopes up in light orange, while a rock-strewn landscape is visible on the far right. Curiosity unexpectedly went into safe mode in early July, but it was brought out last week and has now resumed exploring the once lake-filled interior of Gale Crater for further signs that it was once habitable by microbial life.

APOD: 2016 May 29 - Valles Marineris: The Grand Canyon of Mars
Explanation: Mars will look good in Earth's skies over the next few days -- but not this good. To get a view this amazing, a spacecraft had to actually visit the red planet. Running across the image center, though, is one the largest canyons in the Solar System. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Several geologic processes have been identified in the canyon. The featured mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s. Tomorrow, Mars and Earth will pass the closest in 11 years, resulting in the red planet being quite noticeable toward the southeast after sunset.

APOD: 2014 May 11 - Valles Marineris: The Grand Canyon of Mars
Explanation: The largest canyon in the Solar System cuts a wide swath across the face of Mars. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Several geologic processes have been identified in the canyon. The above mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s.

APOD: 2011 March 27 - Valles Marineris: The Grand Canyon of Mars
Explanation: The largest canyon in the Solar System cuts a wide swath across the face of Mars. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Several geologic processes have been identified in the canyon. The above mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s.

APOD: 2010 May 25 - Looking Back Across Mars
Explanation: It's been a long trip for the Martian rover Opportunity. Last week Opportunity surpassed Viking 1 as the longest running mission on Mars, now extending well over six years. Pictured above, Opportunity's tire tracks cross a nearly featureless Martian desert, emanating from a distant horizon. Landing in 2004 in Meridiani Planum, the robotic Opportunity has embarked on its longest and most dangerous trek yet, now aiming to reach large Endeavor Crater sometime next year. Endeavor, it is hoped, holds new clues to the ancient geology of Mars and whether Mars could once have harbored life.

APOD: 2008 May 26 - A New Horizon for Phoenix
Explanation: This flat horizon stretches across the red planet as seen by the Phoenix spacecraft after yesterday's landing on Mars. Touching down shortly after 7:30pm Eastern Time, Phoenix made the first successful soft landing on Mars, using rockets to control its final speed, since the Viking landers in 1976. Launched in August of 2007, Phoenix has now made the northernmost landing and is intended to explore the Martian arctic's potentially ice-rich soil. The lander has returned images and data initially indicating that it is in excellent shape after a nearly flawless descent. News updates will be available throughout the day.

APOD: 2007 August 28 - Could Hydrogen Peroxide Life Survive on Mars
Explanation: Is there life on Mars? Although no unambiguous evidence for indigenous life on Mars has ever been found, a more speculative question -- could some life forms survive on Mars -- has taken on a new twist. Two planetary scientists recently speculated that were extremophile microbes to involve a mixture of hydrogen peroxide (H2O2) and water (H2O), these microbes might well be able survive the thin, cold, dry atmosphere on Mars. Life that involves hydrogen peroxide does exist here on Earth, they note, and such life would be better able to absorb water on Mars. They also claim that such life would be consistent with the ambiguous results coming out from the life-detecting experiments aboard the old Viking Landers. Although such speculation is not definitive, debating possibilities for life on Mars has again proven to be fun and a magnet for media attention. Pictured above, the Viking Lander 2 captured an unusual image of the Martian surface in 1979 sporting a thin layer of seasonal water ice.

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 July 30 - Valles Marineris: The Grand Canyon of Mars
Explanation: The largest canyon in the Solar System cuts a wide swath across the face of Mars. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Recently, several geologic processes have been identified in the canyon. The above mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s.

APOD: 2005 October 27 - The Last Titan
Explanation: On October 19th, a rocket blasted off from Vandenberg Air Force Base - the last Titan rocket. Carrying a payload for the US National Reconnaissance Office, the successful Titan IV B launch brings to a close the Titan program whose first launch was in 1959. Originally designed as an intercontinental ballistic missile, the Titan rocket ultimately evolved into a heavy lift workhorse, launching defense, commercial, and scientific payloads to Earth orbit and beyond. In fact, many historic space explorations began with Titan launches, including manned Gemini missions, the Viking missions to Mars, the Voyager tours of the outer solar system, and the Cassini spacecraft now orbiting Saturn. Cassini's probe Huygens accomplished the most distant landing on another world, while Voyager 1 is now humanity's most distant spacecraft.

APOD: 2003 December 30 - A Dust Devil Crater on Mars
Explanation: What caused the streaks in this Martian crater? Since the above image shows streaks occurring both inside and outside the crater, they were surely created after the crater-causing impact. 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: 2003 November 29 - Phobos Over Mars
Explanation: Hurtling through space a mere 3,000 miles above the Martian surface, the diminutive moon Phobos (below and left of center) was imaged against the backdrop of a large shield volcano by the Viking 2 Orbiter in 1977. This dramatic picture looks down from the Orbiter's viewpoint about 8,000 miles above the volcano, Ascraeus Mons. Phobos itself is 5,000 miles below the Orbiter. North is toward the top with the Sun illuminating the scene from the South (black dots are reference marks). For scale, Ascraeus Mons is about 200 miles across at its base while asteroid sized Phobos is about 15 miles in diameter. In this spectacular moon-planet image, volcanic calderas (craters) are visible at the summit of Ascraeus Mons -- while impact craters on the sunlit side of Phobos' surface can also be seen!

APOD: 2003 August 24 - Valles Marineris: The Grand Canyon of Mars
Explanation: The largest canyon in the Solar System cuts a wide swath across the face of Mars. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Recently, several geologic processes have been identified in the canyon. The above mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s.

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.

APOD: 2003 April 6 - 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. In this 1978 Viking 1 orbiter image, the largest moon, Phobos, is indeed seen to be a heavily cratered asteroid-like object. About 17 miles across, Phobos really zips through the Martian sky. Actually rising above Mars' western horizon and setting in the east, it completes an orbit in less than 8 hours. But Phobos 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: 2003 February 18 - Candor and Ophir Chasmata
Explanation: First imaged by the Mariner 9 spacecraft, Valles Marineris, the grand canyon of Mars, is a system of enormous depressions called chasmata that stretch some 4,000 kilometers along the Martian equator. Looking north over the canyon's central regions, Candor chasma lies in the foreground of this spectacular view with the steep walls of Ophir chasma near the top. Surface collapse and landslides are seen to be part of the complex geologic history of these dramatic features but recent high resolution images have also revealed layered deposits within the canyon system. This picture represents a mosaic of images recorded in 1978 from Martian orbit by the Viking 1 and 2 spacecraft. The full width of the picture covers about 800 kilometers.

APOD: 2002 August 27 - Valles Marineris: The Grand Canyon of Mars
Explanation: The largest canyon in the Solar System cuts a wide swath across the face of Mars. Named Valles Marineris, the grand valley extends over 3,000 kilometers long, spans as much as 600 kilometers across, and delves as much as 8 kilometers deep. By comparison, the Earth's Grand Canyon in Arizona, USA is 800 kilometers long, 30 kilometers across, and 1.8 kilometers deep. The origin of the Valles Marineris remains unknown, although a leading hypothesis holds that it started as a crack billions of years ago as the planet cooled. Recently, several geologic processes have been identified in the canyon. The above mosaic was created from over 100 images of Mars taken by Viking Orbiters in the 1970s.

APOD: 2001 September 2 - Deimos: A Small Martian Moon
Explanation: Mars has two tiny moons, Phobos and Deimos. Pictured above is Deimos, the smaller moon of Mars. In fact, Deimos is one of the smallest known moons in the Solar System measuring only nine miles across. The diminutive Martian moons were discovered in 1877 by Asaph Hall, an American astronomer working at the US Naval Observatory in Washington D.C. The existence of two Martian moons was predicted around 1610 by Johannes Kepler, the astronomer who derived the laws of planetary motion. In this case, Kepler's prediction was not based on scientific principles, but his writings and ideas were so influential that the two Martian moons are discussed in works of fiction such as Jonathan Swift's Gulliver's Travels, written in 1726, over 150 years before their actual discovery.

APOD: 2001 August 18 - Phobos: Doomed Moon of Mars
Explanation: 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. In this 1978 Viking 1 orbiter image, the largest moon, Phobos, is indeed seen to be a heavily cratered asteroid-like object. About 17 miles across, Phobos really zips through the Martian sky. Actually rising above Mars' western horizon and setting in the east, it completes an orbit in less than 8 hours. But Phobos is doomed. Phobos orbits so close to Mars, (about 3,600 miles above the surface compared to 250,000 miles for our Moon) 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: 2001 July 21 - 25 Years Ago: Vikings on Mars
Explanation: On July 20, 1976, NASA's Viking 1 lander became the first U.S. 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 site 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 continuing its well chronicled martian exploration program as the Mars Odyssey spacecraft is scheduled to arrive at the mysterious Red Planet on October 24th. What's Mars like today?

APOD: 2001 April 17 - Colorful Water Clouds Over Mars
Explanation: One place where water can be found on Mars is in clouds. In the above picture colorful water clouds are visible just after sunrise in and around a maze of canyons known as Noctis Labyrinthus (the labyrinth of the night). Scientists don't yet know, however, why these clouds formed, and why some stick to the canyons. One exciting possibility is that water sometimes condenses in shaded regions of the canyons, only to evaporate into clouds when exposed to the morning Sun. Water in any form on the Martian surface might be important to sustaining life and possible future human exploration. Viking Orbiter 1, which visited Mars in 1976, took the above picture. The region shown is about 100 kilometers across.

APOD: 2001 March 31 - Barsoom
Explanation: "Yes, I have been to Barsoom again ..." begins John Carter in Edgar Rice Burroughs' 1913 science fiction classic "The Gods of Mars". In Burroughs' novels describing Carter's adventures on Mars, "Barsoom" is the local inhabitants' name for the Red Planet. Long after Burroughs' stories were published, Mars continues to inspire Earthdwellers' interests and imagination. Soon it will again be invaded by spacecraft from Earth. This dramatic picture of a crescent Mars was taken by NASA's Viking 2 spacecraft as it approached Barsoom in 1976.

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: May 20, 1999 - Cyclone on Mars
Explanation: Late last month a team of Mars-watching astronomers sighted an immense cyclonic storm system raging near the Red Planet's north pole. Their discovery picture, made with the Hubble Space Telescope on April 27, is seen at left while the projected insets (right) show closeups of the storm and surrounding areas. Shrunken to its martian midsummer state, Mars' north polar cap appears at the top of the discovery picture. The polar cap is clearly smaller than the storm just below it and farther left. Similar to the "spiral storms" detected on Mars over 20 years ago by the Viking spacecraft, this storm was marked by a system of swirling bright water-ice clouds instead of the billowing dust of a more typical martian wind storm. Measuring roughly 1,000 miles across, with a cloud-free central eye spanning about 200 miles, it was comparable in size to cyclones seen in planet Earth's polar regions. The storm system was imaged once more, hours later, but then was not seen again and may have had a lifetime of only a few days.

APOD: April 24, 1999 - Barsoom
Explanation: "Yes, I have been to Barsoom again ..." begins John Carter in Edgar Rice Burroughs' 1913 science fiction classic "The Gods of Mars". In Burroughs' novels describing Carter's adventures on Mars, "Barsoom" is the local inhabitants' name for the Red Planet. Long after Burroughs' stories were published, Mars continues to inspire Earthdwellers' interests and imagination. Soon it will again be invaded by spacecraft from Earth. This dramatic picture of a crescent Mars was taken by NASA's Viking 2 spacecraft in 1976.

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: March 13, 1999 - Phobos Over Mars
Explanation: Hurtling through space a mere 3,000 miles above the Martian surface, the diminutive moon Phobos (below and left of center) was imaged against the backdrop of a large shield volcano by the Viking 2 Orbiter in 1977. This dramatic picture looks down from the Orbiter's viewpoint about 8,000 miles above the volcano, Ascraeus Mons. Phobos itself is 5,000 miles below the Orbiter. North is toward the top with the Sun illuminating the scene from the South (black dots are reference marks). For scale, Ascraeus Mons is about 200 miles across at its base while asteroid sized Phobos is about 15 miles in diameter. In this spectacular moon-planet image, volcanic calderas (craters) are visible at the summit of Ascraeus Mons -- while impact craters on the sunlit side of Phobos' surface can also be seen!

APOD: November 15, 1998 - Deimos: A Small Martian Moon
Explanation: Mars has two tiny moons, Phobos and Deimos. Pictured above is Deimos, the smaller moon of Mars. In fact, Deimos is one of the smallest known moons in the Solar System measuring only 9 miles across. The diminutive Martian moons were discovered in 1877 by Asaph Hall, an American astronomer working at the US Naval Observatory in Washington D.C. The existence of two Martian moons was predicted around 1610 by Johannes Kepler, the astronomer who derived the laws of planetary motion. In this case, Kepler's prediction was not based on scientific principles, but his writings and ideas were so influential that the two Martian moons are discussed in works of fiction such as Jonathan Swift's "Gulliver's Travels", written in 1726, over 150 years before their actual discovery.

APOD: September 19, 1998 - 18 Miles From Deimos
Explanation: Diminutive Deimos is the smallest of the two tiny Moons of Mars. Potato-shaped and barely 6 miles wide this asteroid-like body was visited by the Viking 2 orbiter in 1977. This image was made when the spacecraft approached to within 18 miles of Deimos' surface. One of the most detailed pictures of a celestial body ever taken by an orbiting spacecraft, the field of view is less than a square mile and features just under 10 feet across are visible. Craters and large chunks of rock are seen scattered on the surface while some of the craters appear to be covered by a layer of powdery soil or "regolith".

APOD: May 31, 1998 - Phobos: Doomed Moon of Mars
Explanation: Phobos 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 asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. In this 1977 Viking orbiter image, the largest moon, Phobos, is seen to be a heavily cratered asteroid-like object. It is about 17 miles across and zips through the Martian sky completing an orbit in less than 8 hours. Phobos orbits so close to Mars, (about 3,600 miles above the surface compared to 250,000 miles for our Moon) that gravitational tidal forces are dragging it down. In 100 million years or so it should crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.

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 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 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: July 24, 1997 - Mars Pathfinder's Landing Site
Explanation: Where is Mars Pathfinder? Follow the arrow in the above picture taken by the Viking Orbiter in 1976. From the surface Mars appears covered with rocks, but from orbit Mars appears covered with craters. However, several familiar features are visible in this photograph. To the left (west) of Sagan Memorial Station are the now-familiar twin peaks that dominate the horizon of many Pathfinder photographs. These hills are about one kilometer from the landing site, twice the planned range of Sojourner. Two craters loom nearby: a small one to the east not easily visible here, and a big one to the south of Pathfinder. The landing site is in the dry flood channel named Ares Vallis.

APOD: July 3, 1997 - Mars: A Journey's End
Explanation: Mars Pathfinder is nearing the end of its 7 month journey. The robot spacecraft is scheduled to use parachutes, rockets, and airbags to "bouncedown" on the red planet tomorrow - July 4th. This Hubble Space Telescope image of Mars was taken a few days ago to check on the weather. The pathfinder landing site, on the ancient floodplain Ares Vallis, is just right of center - 500 miles southeast of where Viking 1 landed in 1976. Along with the martian north polar cap, some water ice clouds are visible in both the northern and southern hemisphere. About 600 miles south of the landing site a dust storm can be seen as a brownish ribbon stretching through the the Valles Marineris, a continent sized canyon system. Fortunately, the dust storm is not expected to seriously affect operations at the landing site.

APOD: June 28, 1997 - Barsoom
Explanation: "Yes, I have been to Barsoom again ..." begins John Carter in Edgar Rice Burroughs' 1913 science fiction classic "The Gods of Mars". In Burroughs' novels describing Carter's adventures on Mars, "Barsoom" is the local name for the red planet. Mars continues to inspire Earthdwellers' interests and imagination. Soon it will again be invaded by spacecraft from Earth. This dramatic picture of a crescent Mars was taken by NASA's Viking 2 spacecraft in 1976.

APOD: June 27, 1997 - Mars: Just The Facts
Explanation: Mars, the freeze-dried planet, orbits 137 million miles from the Sun or at about 1.5 times the Earth-Sun distance. It has two diminutive moons, towering extinct volcanos, an immense canyon system, a thin atmosphere chiefly composed of carbon dioxide (CO2), a frigid average surface temperature of -63 degrees Celsius, and permanent frozen CO2 polar caps which contain some water ice. Mars' surface presently lacks liquid water and has a reddish color because of an abundance of oxidized iron compounds (rust). A small terrestrial planet, fourth from the Sun, Mars has only about 3/8 the surface gravity of Earth. So for example, if you tip the scale at a hefty 200 pounds on Earth you'd be a 75 pound featherweight on Mars. The low martian gravity will be good for NASA's Mars Pathfinder spacecraft scheduled to land on Mars next Friday, July 4th. Using rockets, parachutes, and airbags, Mars Pathfinder will be the first spacecraft to touchdown on the planet since the Viking landers in 1976. Pathfinder is also scheduled to begin the first ever mobile surface exploration by releasing the robot rover, "Mars Sojourner".

APOD: May 28, 1997 - Mars: Just The Fiction
Explanation: For centuries, astronomers have observed Mars, patiently compiling many facts and theories. Like a distant mirror of Earth dwellers' hopes and fears for the future, Mars, the fourth planet from the sun, has inspired profound works of fiction as well. Classics of the science fiction genre with visions of Earth's alluring planetary neighbor include H.G. Wells' terrifying "War of the Worlds", Edgar Rice Buroughs' John Carter adventure series (Thuvia, Maid of Mars, The Gods of Mars, A Princess of Mars, The Warlord of Mars), Robert Heinlein's youthful "Podkayne of Mars", and Ray Bradbury's reflective and philosophical "The Martian Chronicles". Through the years scientific theories about Mars have been disproven, but the sense of wonder and adventure embodied in these works of fiction remain with us. As two spacecraft from Earth now draw close to the red planet- in dreams, desires, and a quest for knowledge - we are once again bound for Mars.

APOD: December 22, 1996 - 18 Miles From Deimos
Explanation: Diminutive Deimos is the smallest of the two tiny Moons of Mars. Potato shaped and barely 6 miles wide this asteroid-like body was visited by the Viking 2 orbiter in 1977. This image was made when the spacecraft approached to within 18 miles of Deimos' surface. It is one of the most detailed pictures of a celestial body ever taken by an orbiting spacecraft - the field of view is less than a square mile and features just under 10 feet across are visible. Craters and large chunks of rock are seen scattered on the surface. Some of the craters appear to have been covered by a layer of regolith (soil and broken rock).

APOD: October 15, 1996 - Phobos Over Mars
Explanation: Hurtling through space a mere 3,000 miles above the Martian surface, the diminutive moon Phobos (below and left of center) was imaged against the backdrop of a large shield volcano by the Viking 2 Orbiter in 1977. This dramatic picture looks down from the Orbiter's viewpoint about 8,000 miles above the volcano, Ascraeus Mons. Phobos itself is 5,000 miles below the Orbiter. North is toward the top with the Sun illuminating the scene from the South (black dots are reference marks). For scale, Ascraeus Mons is about 200 miles across at its base while asteroid sized Phobos is about 15 miles in diameter. In this spectacular moon-planet image, volcanic calderas (craters) are visible at the summit of Ascraeus Mons -- while impact craters on the sunlit side of Phobos' surface can also be seen!

APOD: August 17, 1996 - A Meteorite From Mars
Explanation: The famous Martian meteorite pictured above houses microscopic structures interpreted by many as fossils of ancient Martian life. How do you find a meteorite from Mars here on Earth? On a typical day, several large rocks fall to Earth from space, usually winding up in the oceans. If they do not burn up in the Earth's atmosphere they are called meteorites. (Danger from falling meteorites is rare: the average person would have to repair meteorite damage to their home about every 100 million years.) Most meteorites falling on land are never located or identified - appearing similar to other rocks to the untrained eye. In certain places in Antarctica, however, meteorites stand out from the white frozen ice and snow beneath them, as if they were just left yesterday. When the above meteorite was found in Antarctica, it was considered unusual because of its grey color. So far, about 12 Martian meteorites of similar mineral compostion have been found. One of these contains minute pockets of gases identical in isotopic composition to the Martian atmosphere as determined from the Viking measurements - implying the rocks indeed originated on Mars. These Martian meteorites are typically 1.3 billion years old or less, however, the one containing the potential microfossils appears to have an age of about 4.5 billion years.

APOD: July 22, 1996 - Utopia on Mars
Explanation: The Viking 2 spacecraft was launched on the Road to Utopia in September of 1975 (30 years after Bing, Dotty, and Bob). In August of 1976, after making the second successful Martian landing, Viking 2's lander began recording data used to produce this exquisitely detailed image of the Martian surface in the area of Utopia Planitia (the Plain of Utopia). Visible at the lower right are the protective shroud that covered the lander's soil collector head, ejected after the descent, along with one of the lander's dust covered footpads. Seen near the center are shallow trenches dug by the sampler arm. Mars looks red because its surface is covered with reddish iron oxide dust (rust). This dust, suspended in the thin carbon dioxide atmosphere, also filters the sunlight causing surface views to take on a reddish tinge. The Vikings made the first successful landings on Mars 20 years ago. What does Mars look like today?

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?

APOD: February 7, 1996 - If You Could Stand on Mars
Explanation: If you could stand on Mars - what would you see? Viking 1 robot landers answered this question in 1976 with pictures like the one shown above. The dark rocks, red soil, and green-tinged sky grace this rendition of a normal Martian afternoon. At the bottom corners of the picture are portions of Viking spacecraft. The red color of the rocks is caused by an abundance of iron in the soil. The Martian surface is covered by rocks, huge craters, fantastic canyons, and gigantic volcanoes that dwarf any on Earth. No life has been found, but some speculate that since not all spacecraft reaching Mars from Earth had been fully decontaminated, Earth born microbes might live there now.

APOD: February 3, 1996 - A Huge Impact Crater on Mars
Explanation: What hit Mars? The impact crater Schiparelli near the center of the above image was likely caused by a collision with an object the size of an asteroid. Also evident in this full face mosaic of Mars are numerous craters from many other impacts with smaller objects over billions of years. At the lower right, white carbon dioxide frost can be seen in the Hellas basin. The frost forms because temperatures can drop as low as -140 degrees Celsius on Mars. Some Martian regions, however, occasionally reach as high as 20 degrees Celsius - a typical room temperature here on Earth.

APOD: December 14, 1995 - An Atlas Centaur Rocket Launches
Explanation: Atlas Centaur rockets have launched over 75 successful unmanned missions. These missions included the Surveyor series - the first vehicles to make soft landings on the Moon, Pioneer 10 and 11 - the first missions to fly by Jupiter and Saturn and the first man-made objects able to leave our Solar System, the Viking missions which landed on Mars, several satellites in the High Energy Astrophysics Observatory (HEAO) series, Pioneer Venus which circled and mapped the surface of Venus, and numerous Intelsat satellites. Of recent scientific interest was the Atlas launched SOHO mission which will continually observe the Sun. Atlas rockets are manufactured by Lockheed Martin Co.

APOD: October 3, 1995 - Deimos: Small Martian Moon
Explanation: Mars has two tiny moons, Phobos and Deimos. Pictured above is Deimos, the smallest moon of Mars. In fact, Deimos is the smallest known moon in the Solar System measuring only 9 miles across. The diminutive Martian moons were discovered in 1877 by Asaph Hall, an American astronomer working at the US Naval Observatory in Washington D.C. The existence of two Martian moons was predicted around 1610 by Johannes Kepler, the astronomer who derived the laws of planetary motion. In this case, Kepler's prediction was not based on scientific principles, but his writings and ideas were so influential that the two Martian moons are discussed in works of fiction such as Jonathan Swift's "Gulliver's Travels", written in 1726, over 150 years before their actual discovery.

APOD: October 2, 1995 - Phobos: Doomed Moon of Mars
Explanation: 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 asteroid belt between Mars and Jupiter or perhaps from even more distant reaches of the Solar System. In this 1977 Viking orbiter image, the largest moon, Phobos, is seen to be a heavily cratered asteroid-like object. It is about 17 miles across and zips through the Martian sky completing an orbit in less than 8 hours. Phobos is doomed. It orbits so close to Mars, (about 3,600 miles above the surface compared to 250,000 miles for our Moon) that gravitational tidal forces are dragging it down. In 100 million years or so it could crash into the surface or be shattered by stress caused by the relentless tidal forces, the debris forming a ring around Mars.

APOD: July 22, 1995 - The Face on Mars
Explanation: This image, showing what looks to be a human face sculpted on the martian surface, was produced using data from NASA's Viking 1 orbiter in 1976. Described in a press release as a "face-like hill" it caused some to offer the sensational speculation that it was an artificial construct built by an intelligent civilization on Mars! As a result, this image was splashed across the covers of many grocery store tabloids at the time. A detailed analysis of multiple images of this feature reveals a natural looking martian hill whose illusory face-like appearance depends on viewing angle and angle of illumination.

APOD: July 21, 1995 - The Search for Life on Mars
Explanation: Although images of Mars taken from space revealed the planet to have a barren and cratered surface, scientists did not give up the search for martian life. In 1976 NASA's Viking project succeeded in landing two robot probes on the surface of Mars. These landers were able to carry out sophisticated chemical experiments to look for signs of microscopic life in the martian soil. However, the experiments failed to produce any convincing evidence for life on Mars. Cameras onboard the Viking Landers also returned spectacular photos of the rocky martian landscape, like the one above, which showed no sign of martian animal or plant life.

APOD: July 20, 1995 - The Grand Canyon of Mars
Explanation: The Mariner Valley, also known as the Valles Marineris canyon system, appears in this mosaic of images from NASA's Viking spacecraft as a huge gouge across the red planet. This "Grand Canyon" of Mars is about 2500 miles long and up to 4 miles deep. By comparison, the Earth's Grand Canyon is less than 500 miles long and 1 mile deep.

APOD: July 19, 1995 - The Mountains of Mars
Explanation: Volcanic activity on Mars has produced towering mountains. The largest one, Olympus Mons, is pictured here in this Viking Orbiter image. Olympus Mons is a shield volcano nearly 15 miles high and over 300 miles wide at its base. By comparison, Earth's largest volcano, Mauna Loa in Hawaii, is just over 5 miles high and about 12 miles wide.

APOD: July 17, 1995 - Barsoom
Explanation: "Yes, I have been to Barsoom again ..." begins John Carter in Edgar Rice Burroughs' 1913 science fiction classic "The Gods of Mars". In Burroughs' novels describing Carter's adventures on Mars, "Barsoom" is the local name for the red planet. Long after Burroughs' stories were published, Mars has continued to capture the imagination of science fiction writers as a popular location for extraterrestrial adventures. This dramatic picture of a crescent Mars was taken by NASA's Viking 2 spacecraft in 1976.

APOD: July 16, 1995 - The Exploration of Mars
Explanation: Thirty years ago NASA's exploration of Mars began. In July of 1965 the Mariner 4 spacecraft flew within 6,000 miles of Mars and returned 21 pictures of the mysterious red planet. NASA's continued exploration of Mars has produced detailed views of the red tinged Martian surface like the one shown above which is a composite of 102 images from the Viking missions to Mars . The composite was constructed by the US Geological Survey.