The surface (panoramas) of Mars would be a harsh place for
humans, but it is more like the surface of Earth than any other planet. The
temperature on Mars does not get much cooler than the temperature at Antarctica. At
the surface it ranges from about -140° C to 15° C (about -225° F to 60° F).
During most of the year wind speeds are fairly low—about 7.0 km/h (about 4.5
mph)—but during dust storms they can approach 70 to 80 km/h (40 to 50 mph).
These winds often originate in large basins in the southern hemisphere and carry large
volumes of dust from the basins to other regions, sometimes covering the entire planet in
the storm. The dust is not sandy, as in a sandstorm on the earth, but has the
consistency of flour.
The northern and southern hemispheres of Mars have different
characteristics concerning their geology. The
southern hemisphere of Mars is predominantly ancient
cratered highlands (left) somewhat similar to the Moon.
The southern highlands are probably the oldest terrain
(video) on Mars. In contrast, most of the northern hemisphere consists of
plains which are much younger, lower in elevation and have a much more complex history. The northern hemisphere of Mars contains a much wider variety of geologic
features, including large volcanoes, a great rift valley, craters
and plains, and a variety of channels. The northern hemisphere also contains
large expanses of relatively featureless plains. An abrupt elevation change
of several kilometers seems to occur at the boundary. The reasons for this global
dichotomy and abrupt boundary are unknown (some speculate that they are due to a very
large impact shortly after Mars' accretion). Recently, some scientists have begun
to question whether the abrupt elevation is real in the first place. Mars Global Surveyor should resolve the issue.
Mars has the largest volcano in the solar system, Olympus Mons. It is 26 km (16 miles) high (almost twice as high as the earth’s Mount Everest) and covers an area comparable to the state of Arizona. Near it, three other volcanoes almost as large—Arsia Mons, Pavonis Mons, and Ascraeus Mons—form a line running from southwest to northeast. These four volcanoes are the most noticeable features of a large bulge in the surface of Mars, called Tharsis. Another volcano, Alba Patera, is also part of the Tharsis bulge, but is quite different in appearance. It is probably less than 6 km (4 mi) high, but has a diameter of 1600 km (1000 mi). None of Mars’s volcanoes appear to be active.
The Tharsis bulge has had a profound effect on the appearance of the surface of
Mars. The Tharsis bulge includes many smaller volcanoes and stress fractures, in
addition to the large volcanoes. Its presence affects the weather on Mars and may
have changed the climate by changing the rotation of the planet. Valles Marineris (named for the U.S. Mariner spacecraft that
discovered it) is the most notable stress feature associated with the Tharsis bulge.
It is a great rift valley extending from the Tharsis region away to the
east-southeast. It is about the same length as the distance from New York to California.
This canyon system reaches widths of 700 km (440 mi) and depths of 7 km (4 mi).
Hellas Planitia is a giant impact basin in the southern hemisphere. The impact of a large meteorite formed the basin long ago. With a diameter of about 2000 km (about 1250 mi), it is the largest such basin on Mars.
Three types of channels on Mars may have been formed by the action of water. These channels are unrelated to the "canals" thought to be seen in early telescopic views of Mars. Channel networks are similar in appearance to streambeds on the earth and occur in the southern highlands. These channels may date from a time early in Mars’s history when the atmosphere was thicker and liquid water could flow on the surface. Outflow channels, which giant floods may have formed, occur on the boundary between the southern highlands and the northern plains regions. Ares Vallis, where the Mars Pathfinder spacecraft was scheduled to land, is one of these outflow channels. Landslides and other erosion probably formed fretted channels by enlarging preexisting channels.
Mars has small, permanent ice caps at its north and south poles. The caps increase in size in the winter of each hemisphere. The caps in the north and south are quite different from one another. The northern permanent cap is composed of water ice and is about 1000 km (about 620 miles) across. A seasonal cap of frozen carbon dioxide adds to the northern ice cap in the northern winter. The southern permanent cap is one-third the diameter of the northern cap because summer in the southern hemisphere is warmer than in the north. The southern seasonal cap is larger than the northern cap—more carbon dioxide is frozen out in the south than the north because Mars is farthest from the sun, and therefore coldest, in the southern winter. Carbon dioxide may also make up the southern permanent cap.
Regions of striped-looking terrain, probably formed of layers of dust and ice, occur at the edges of both polar caps. Climate cycles almost like the ice ages on the earth may have caused this layering.