Early Mars: Oceans Away? |Even the youngest craters on Mars
display lobate ejecta patterns that may indicate subsurface
water or ice. Credit: National Air and Space Museum During the
1970s, photos from the first Mars orbiters showed dry river
channels that were apparently quite ancient - dating from the
first 500 million years of the planet's existence. The river
valleys implied liquid water, raising the possibility that life
might have developed. Today, the Martian surface is cold and
dry, and astronomers and climate modelers have struggled to
explain such warm conditions in the early years, when the sun
was considerably weaker. The leading theory is that early Mars
had a thicker atmosphere, which generated a potent greenhouse
effect. But to some researchers, this idea seems insufficient to
account for above-freezing temperatures. Owen Toon, of the
laboratory for atmospheric and space physics at the University
of Colorado, says greenhouse gases cannot explain the presence
of liquid water on early Mars. "Ther