Mars From Afar

The Planet
This is Mars as it appeared in May 2002. It's early spring in the Northern Hemisphere, whose seasonal carbon-dioxide frost cap has begun its annual retreat. Other white areas in this composite are clouds, some seen hovering over volcanoes such as Olympus Mons, the dark round spot in the far left of the image. The huge canyon system known as Valles Marineris is visible as a thick horizontal line in the lower right. All told, Mars is about 4,200 miles in diameter, a little over half as big across as the Earth.

Canyon
In the center of this mosaic of Mars lies the Valles Marineris, the largest known chasm in the solar system. It stretches over 1,860 miles from west to east, and in places reaches five miles in depth. (The Grand Canyon, at its deepest, is just over a mile from rim to river.) Huge rivers once flowed north from the chasm's north-central canyons to a vast basin called Acidalia Planitia (the dark area in the top right of the image). To the west of the Valles Marineris you can see three ancient volcanoes (dark brown circles), each about 15 miles high. This mosaic consists of 102 images from the Viking Orbiter, and the viewer's distance is 1,550 miles above the surface.

Volcano
This mosaic of images taken by Viking 1 on June 22, 1978, shows Olympus Mons, the highest known volcano in the solar system. Its summit caldera lies over 78,500 feet above the surrounding plains, making it over two and a half times the height of Mt. Everest. The volcano proper, defined by the roughly circular cone visible in the center of the image, is about 340 miles in diameter, revealing just how gradual a slope the mountain's flanks display. Encircling the volcano is a moat of lava thought to have come from Olympus Mons.

Volcanic Vent
This deep trough lies in the Tharsis region of Mars, home to several of the largest shield volcanoes in the solar system. It is a volcanic vent, where lava erupted long ago. The shallow, scalloped depressions in the middle and left (west) of the image may have been lava lakes that emptied into the vent at the end of the eruption that created the vent. To the right (east) are two channels that once likely drained the vent. Once deeper and narrower, the vent became more trough-like as material eroded from its sides and fell to its floor. The image was taken on December 6, 2006, by the High Resolution Imaging Science Experiment.

Sand Dunes
Resembling a group of horseshoe crabs coming ashore, windblown sand dunes grace the floor of Wirtz Crater. The shape of the dunes indicates that the wind has blown the sand from the southwest toward the northeast (lower left to upper right in the image). Illuminated by sunlight streaming in from the northwest, the scene comprises an area less than two miles in width.

Crater
Looking like it might have been blasted out yesterday, this impressive meteor impact crater lies in the northern Elysium Planitia, the second largest volcanic region on Mars. The crater's diameter is a little over twice that of Meteor Crater in Arizona (which is three quarters of a mile wide and our planet's best preserved impact crater). Darkening more than half the crater, the shadow gives an idea of just how deep the basin is.

Ice Cap
Dubbed martian "Swiss cheese," these raised sections of ice in the south polar ice cap and the circular depressions within them may be a combination of water ice and frozen carbon dioxide, or "dry ice." The area covered in this image is 1.9 by 5.6 miles, and the tallest portions of the raised ice mesas are about 14 feet high.

Polar Gas Channels
Known informally as a "spider," the topographic feature seen in this image of Mars' south polar region represents a process not found on Earth. The branching tendrils contain carbon dioxide gas, which flows through the channels until it reaches a vent; it then escapes to the atmosphere, carrying dust with it. The tendrils, appearing bright-white with the carbon dioxide ice that covers the poles during winter, weave into the surrounding icy terrain, which, in turn, is blanketed by the region's characteristic reddish-brown dust. The image was taken on March 24, 2007, by the High Resolution Imaging Science Experiment.

Faulting
The deep trough slashing diagonally across the center of this image resulted from faulting and down-dropping of the land. Boulders the size of small buildings can be seen on the slopes of this depression, which is sunlit from the left. Dark streaks on the trough's slopes are the paths of small landslides. This trough and the shallower one in the lower part of the image cut across lava flows, suggesting that the trenches formed after the lava had cooled and hardened. Short, parallel ridges in the valley floors are probably dunes.

Layered Rocks
Water or wind deposited the sediments that are thought to make up these layered rock outcroppings. Wind later shaped and exposed the layers, which on close inspection resemble those on a topographical map. Note the dark drifts of sand in the lower center of the image, which is illuminated by sunlight coming from the upper left. The scene is in the bottom of an impact crater near the martian equator.

Gullies
Not dramatically different from a mountainside in, say, the American Southwest, this weathered wall of a crater displays gullies that might have been carved by groundwater flowing downhill. Wintertime frost dusts the wall, while below on the crater floor you can see dunes sculpted by the wind. The Mars Global Surveyor's narrow-angle camera took the shot, which was then "colorized" using actual colors of the surface obtained by the spacecraft's wide-angle cameras.

Clouds
One early martian afternoon in April 1999, the Mars Orbiter Camera (MOC) captured this view of diaphanous clouds floating over the summit of Apollinaris Patera, a volcano near the planet's equator. The various impact craters pockmarking its crater and flanks indicate how ancient the volcano is. It is also enormous: An estimated three miles high, its summit caldera alone is about 50 miles across. The color in this image was derived from the MOC's red and blue wide-angle camera systems and does not represent true color as you would see it with the naked eye.

Mesas
To some viewers, the spaghetti-like forms captured in this image may at first glance appear raised from the surface, but they are actually troughs separating layered mesas. Pitting and erosion fashioned the mesas, which are lit by the sun from the lower left. Dust cloaks the landscape, and large, wind-crafted ripples can be seen on the trough floors. The image is slightly less than two miles wide.

Landslide
Sometime in the distant past, a large portion of this slope in the Kasei Valles region gave way and slid down into the valley below. Scientists know it was a long time ago because of the impact craters apparent in both the landslide's scar and its resulting deposit. At the base of the scar, just below the slightly oval-shaped impact crater, you can see numerous black dots. These are house-sized boulders that have tumbled down from higher up the 660-foot slope. Near the cornice, you can just make out layers in the bedrock revealed by the landslide.

Plains
Like certain high-latitude areas in the Northern Hemisphere on Earth, the northern plains of Mars often show patterned ground. Whether this stippled surface indicates ground ice, as similar-looking surfaces do in parts of Alaska, Canada, and Siberia, is unknown. In this image, taken at a latitude of 72.4°N, the dark dots and lines are low mounds and chains of mounds, respectively. Note the buried impact crater in the center of the image, which is about 1.9 miles across.

Dust Storms
In late June 2001, as the martian southern winter gave way to spring, dust storms began to kick up as cold air from the south polar ice cap moved north toward warmer air at the equator. By early July, dust storms had cropped up all over the planet, whose surface, by the end of the month, had become almost entirely obscured, as if by a single, global storm. By late September, the storms had largely abated, though the atmosphere remained hazy into November.

Terrain
Mars Pathfinder's stereo imaging system took a series of photographs that were used to create this 360-degree "geometrically improved, color-enhanced" panorama of the surface of Mars. The images were made over the course of three martian days to ensure consistent lighting and shadows across the panorama. In the lower portion of the image, you can see the lander, with its opened petals, deflated airbags, and pair of ramps. The Sojourner rover descended the rear (right) ramp to the surface, then made its way to the large rock, dubbed "Yogi," where it is using its Alpha Proton X-Ray Spectrometer to study the rock's composition. The "Twin Peaks" visible on the horizon are less than a mile and a quarter away.

Frozen Water
Use the slider (in enlarged version) to compare these two color images from the Phoenix Mars Lander, which touched down on the Red Planet on May 25, 2008. The lander's Surface Stereo Imager took these pictures on June 15 and June 19, respectively. The pictures show sublimation—the passing of a substance, in this case ice, directly from a solid to a gas—in a lander-dug trench over the course of four days. In the lower left of the lefthand image, a group of white lumps is visible within the shadow; in the righthand image, they're gone. Look closely also at the white patches in full sun—other loss of ice can be seen there. These images confirmed the presence of water ice in the subsoil of the martian arctic.

The Planet, Again
This QuickTime VR, or full-round panorama, was created from a photo-mosaic of images captured over a five-year period by the Viking orbiters in the 1970s. The smooth areas of the globe are geologically younger than the cratered areas, which are ancient. In places, cliffs of up to a mile and a quarter in height separate the two areas. Some Mars experts speculate that water may have once covered the Northern Hemisphere, which is smoother and younger than the Southern. Note bright and dark streaks on the martian surface; these point to active wind processes on Mars.

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