Why is Mars So Dry?

[Lionel]

The MER rovers Spirit and Opportunity, now traveling on the surface of Mars, are exploring a geography drier than the driest desert on Earth. Despite the polar ice caps and suspected pockets of liquid water beneath the martian surface, the amount of water on Mars is but a teaspoon compared to the vast watery reserves of Earth. Why is Mars so dry?The inner planets of our solar system - Mars, Earth, Venus and Mercury - formed by the accumulation of small rocks and dust that swirled around the sun in its earliest years. If the Earth and Mars are made of the same stardust, they should have been born with about the same ratio of water. Many scientists think Mars once was very watery, but lost its oceans due to the low mass of the planet. This, combined with a thin atmosphere, allowed most of the water on Mars to evaporate out into space.But according to a study by Jonathan Lunine of the Lunar and Planetary Laboratory at the University of Arizona, the Red Planet was dry from the very beginning.

Lunine, writing in the journal Icarus in 2003 with colleagues John Chambers, Alessandro Morbidelli, and Laurie Leshin, says that Mars was originally a planetary embryo. In essence, a planetary embryo is a very large asteroid that can be as massive as Mercury or Mars. This pre-Mars embryo existed in the asteroid belt, which at the time was more widely dispersed in the solar system, spread out between 0.5 to 4 AU from the sun. Today the main asteroid belt is roughly at 2 to 4 AU, located between Mars (1.5 AU) and Jupiter (5.2 AU).

View: Full Article | Source: Astrobiology Magazine