MARS

Mars Mars imaged by the Hubble Space Telescope.
Oppositions Illustration of some recent Martian oppositions.
Valles Marineris The giant canyon Valles Marineris stretches across the globe of Mars.
Martian Scenes Some beautiful renderings of the Martian surface by Kees Veenenbos using the Mars Orbital Laser Altimeter data from the Mars Global Surveyor and the landscape generator Terragen.
Mars1 3D The Martian Moon Phobos from the Viking Orbiter, 1977.
Mars2 3D Acheron Fossae. A set of parallel fault-bounded valleys. Uplift caused the crust to fracture.
Mars3 3D Ma'adum Vallis. This is an channel probably formed by a large water flow 3.5 billion years ago.
Mars4 3D Valles Marineris. A huge rift formed by uplift.
Mars5 3D Tithonium Chasma. One portion of Valles Marineris. It is 50 km wide and 6 km deep.
Mars6 3D Rahe Crater. A degraded old crater with a sand dune field in the center.
Mars7 3D Protonilus Mensae. A crater that has been eroded right down the middle.
Mars8 3D A 220 degree panorama of the Viking I landing site.
Mars9 3D A 220 degree panorama of the Viking 2 landing site.
Olympus The giant Martian volcano, Mt. Olympus.
Surface1 An image of the Martian surface from the Viking 2 lander.
Surface2 The Martian surface on May 18, 1979 from the Viking 2 lander. A thin coating of water ice can be seen.
Surface3 Images of the Martian surface taken by the Pathfinder mission.
Surface4 A collection of images of the Martian surface taken by the Viking landers.
Surface5 A collection of images taken by the Spirit Rover.
Surface6 A collection of images taken by the Mars Opportunity Rover.
Sky1 The Martian twilight sky seen from the Pathfinder Lander.
Dunes1 Dark streaks on the steep, down-wind slopes of sand dunes in Rabe Crater are seen at several locations in this Mars Global Surveyor image. These streaks indicate relatively recent (i.e., in the past few years or less) movement of sand down these slopes.

Sand dunes move forward by the combined action of wind that drives sand up the shallow slope on the windward side of the dune (in this case, the slopes that face toward the lower right) and the avalanching of this sand down the steeper, lee-side slope. The steep slope is also known as the slip face. The dark streaks indicated by arrows are evidence for sand avalanches that occurred within a few months or years of the time when the picture was taken in March 1999. Other streaks which are seen criss-crossing the dunes may be the result of passing dust devils. 
Dunes2 Sand dunes in the Martian crater Herschel.
DustDevil1 Many Mars Global Surveyor images of the middle latitudes of the northern and southern hemispheres of Mars show wild patterns of criss-crossing dark streaks. Many of these streaks are straight and narrow, others exhibit curly arcs, twists, and loops. They often cross over hills, run straight across dunes and ripples, and go through fields of house-sized boulders. This picture covers an area 3 km by 5 km (1.9 by 3.1 miles). 
DustDevil2 For many months scientists were seeing streaks such as these, but were uncertain how they formed. One speculation was that they might result from the passage of dust devils. Each dust devil would leave a dark streak by removing bright dust from the terrain in its path, revealing a darker surface underneath.
DustDevil3 A dust devil was caught in the act of creating a swirly, dark streak! The dust devil was traveling from right (east) to left (west). A columnar shadow was cast by sunlight coming from the upper left. This shadow indicates the true shape of the dust devil. The bright dust devil itself does not look like a column because the picture was taken from a camera looking straight down on it. The dust devil is less than 100 meters (less than 100 yards) wide and the picture covers an area approximately 1.5 by 1.7 kilometers (about 1 by 1 mile).

Dust devils are spinning, columnar vortices of wind that move across the landscape, pick up dust, and look somewhat like miniature tornadoes. Dust devils are a common occurrence in dry and desert landscapes on Earth as well as Mars. They form when the ground heats up during the day, warming the air immediately above the surface. As the warmed air nearest the surface begins to rise, it spins. The spinning column begins to move across the surface and picks up loose dust (if any is present). The dust makes the vortex visible and gives it the "dust devil" or tornado-like appearance. On Earth, dust devils
typically last for only a few minutes.
Dust Storm1 In this figure a dust storm on Mars is compared with one that occurred on Earth. The top image shows a martian north polar dust storm observed on 29 August 2000. The storm is moving as a front, outward from a central "jet," and marginal "vortices" can be seen. In this image it extends about 900 km (560 mi) out from the north polar seasonal frost cap. The region on the right side of the Mars picture includes the north pole. The bottom image shows a terrestrial dust storm seen on 26 February 2000. This storm extends about 1800 km (1100 mi) off the coast of northwest Africa near the Earth's equator. Both images are shown at the same scale; 4 km (2.5 mi) per pixel.
PolarCaps1 This is a wide angle view of the martian north polar cap as it appeared to the Mars Global Surveyor in early northern summer. The picture was acquired on March 13, 1999. The light-toned surfaces are residual water ice that remains through the summer season. The nearly circular band of dark material surrounding the cap consists mainly of sand dunes formed and shaped by wind. The north polar cap is roughly 1100 kilometers (680 miles) across.
PolarCaps2 This is the south polar cap of Mars as it appeared to the Mars Global Surveyor on April 17, 2000. In winter and early spring, this entire scene would be covered by frost. In summer, the cap shrinks to its minimum size, as shown here. Even though it is summer, observations made by the Viking orbiters in the 1970s showed that the south polar cap remains cold enough that the polar frost (seen here as white) consists of carbon dioxide. Carbon dioxide freezes at temperatures around -125 degrees C (-193 degrees F). The south polar cap from left to right is about 420 km (260 mi) across.
PolarCaps3 The edge of the northern Martian polar cap meets a dune field.
PolarCaps4 Vertical cliffs about 2 KM high near Mars' North Pole.
Shadow The images show a wide angle red (left), blue (middle), and color composite (right) view of the shadow of Phobos (elliptical feature at center of each frame) as it was cast upon western Xanthe Terra on August 26, 1999, at about 2 p.m. local time on Mars. The image covers an area about 250 kilometers (155 miles) across and is illuminated from the left. Note the dark spots on three crater floors--these appear dark in the red camera image (left) but are barely distinguished in the blue image (middle) while the shadow is dark in both images. The spots on the crater floors are probably small fields of dark sand dunes.

If you could stand on Mars and watch Phobos passing overhead, you would notice that this moon appears to be only about half the size of what Earth's Moon looks like when viewed from the ground. In addition, the Sun would seem to have shrunk to about 2/3 (or nearly 1/2) of its size as seen from Earth. Martian eclipses are therefore dark but not as spectacular as total solar eclipses on Earth can be. In compensation, the Martian eclipses are thousands of times more common, occurring a few times a day somewhere on Mars whenever Phobos passes over the planet's sunlit side.

Phobos Spectacular close-up images of the giant crater on the Martian moon Phobos.
Deimos The Martian moon Deimos images by Viking 2.
Water Various images showing evidence that water once existed on Mars.
Clouds Water clouds visible at sunrise in a canyon area called Noctis Labyrinthus. (Viking1)