Arabia Terra is a large upland region in the north of Mars that lies mostly in the Arabia quadrangle, but a small part is in the Mare Acidalium quadrangle. It is densely cratered and heavily eroded. This battered topography indicates great age, and Arabia Terra is presumed to be one of the oldest terrains on the planet. It covers as much as 4,500 km (2,800 mi) at its longest extent, centered roughly at 21°N 6°E with its eastern and southern regions rising 4 km (13,000 ft) above the north-west. Alongside its many craters, canyons wind through the Arabia Terra, many emptying into the large northern lowlands of the planet, which borders Arabia Terra to the north.
THEMIS daytime infrared image mosaic showing Eden Patera (at center), one of the proposed volcanic caldera complexes in Arabia Terra, and its surroundings
Ice sheet in Oxus Patera, a caldera in Arabia Terra. The scalloped nicks along the spines of the caldera's ridges are likely cracks caused by the expansion and contraction of ice.
Layers in Tikhonravov Crater in Arabia, as seen by Mars Global Surveyor (MGS). Layers may form from volcanoes, the wind, or by deposition under water. The craters on the left are pedestal craters. Some researchers believe this crater once held a massive lake.
Tikhonravov Crater floor, as seen by Mars Global Surveyor. Click on image to see dark slope streaks and layers.
Mars is the fourth planet from the Sun. The surface of Mars is orange-red because it is covered in iron(III) oxide dust, giving it the nickname "the Red Planet". Mars is among the brightest objects in Earth's sky and its high-contrast albedo features have made it a common subject for telescope viewing. It is classified as a terrestrial planet and is the second smallest of the Solar System's planets with a diameter of 6,779 km (4,212 mi). In terms of orbital motion, a Martian solar day (sol) is equal to 24.5 hours and a Martian solar year is equal to 1.88 Earth years. Mars has two natural satellites that are small and irregular in shape: Phobos and Deimos.
Comparison: Earth and Mars
Curiosity's view of Martian soil and boulders after crossing the "Dingo Gap" sand dune
Valles Marineris, taken by the Viking 1 probe
Edge-on view of Mars atmosphere by Viking 1 probe