Wednesday, September 30, 2009

Water in Mars

Clearly visible on images produced by Martian probes are runoff and outflow channels,
which are believed to be dry river beds, evidence that water once flowed as a liquid
on Mars. Geological evidence dates the Martian highlands to four billion years
ago, the time in which water was apparently sufficiently plentiful to cause widespread
flooding. Recent theories suggest that at the time, Mars had a thicker atmosphere that
allowed water to exist in a liquid state, even at its low surface temperatures.
The Mars Global Surveyor mission, which has established an orbit around the red
planet and is transmitting early data back to the earth, has found further geological
evidence for the presence of liquid and subsurface water. Such evidence has kept alive
hopes that life may have existed—or may even yet exist, perhaps on a microbial
level—on Mars.

Volcanoes, Craters, and a “Grand Canyon”

The Mariner series of planetary probes launched in the 1960s and 1970s revealed a startling difference between the southern and northern hemispheres of Mars. The southern hemisphere is far more cratered than the northern hemisphere, which is covered with wind-blown material as well as volcanic lava. There have even been recent proposals that the smooth northern hemisphere hides a frozen ocean.
Volcanoes and lava plains from ancient volcanic activity abound on Mars. Because the planet’s surface gravity is low (0.38 that of the earth), the volcanoes can rise to spectacular heights. Like Venus, Mars lacks a strong magnetic field, but, in contrast to Venus, it rotates rapidly; therefore, astronomers conclude that the core of Mars is nonmetallic, nonliquid, or both. Astronomers believe that the core of the smaller Mars has cooled and is likely solid, consisting largely of iron sulfide.
Unlike the earth, Mars failed to develop much tectonic activity (instability of the crust), probably because its smaller size meant that the outer layers of the planet cooled rapidly. Instead, volcanic activity was probably quite intense some 2 billion years ago.
Also impressive are Martian canyons, including Valles Marineris, the “Mariner
Valley,” which runs some 2,500 miles (4,025 km) along the Martian equator and is as
much as 75 miles (120 km) wide and, in some places, more than four miles (6.5 km)
deep. The Valles Marineris is not a canyon in the earthly sense, since it was not cut
by flowing water, but is a geological fault feature.

Why Mars Is Red

If we feel any disappointment at the loss of our cherished Martian canals, at least we can still enjoy the image of the “angry red planet.” Yet the source of the reddish hue is not the bloody spirit of the Roman god of war, but simple iron ore. The Martian surface contains large amounts of iron oxide, red and rusting. As Viking 1 and Mars Pathfinder images revealed, even the Martian sky takes on a rust-pink tinge during seasonal dust storms.
The dust is blown about by winds that kick up in the Martian summer. These winds play a prominent role on Mars, forming vast dunes and streaking craters. An especially large dune is found around the north polar cap.