Space is dangerous. Asteroids and comets zoom through the solar system, occasionally smashing into the planets and moons. But things were a lot worse four billion years ago, when the solar system was filled with many more asteroids and comets.
Because Earth is so active, its scars have mostly healed. Not so for its neighbor, the planet Mars, which climbs into view by mid-evening and looks like a brilliant orange star. It has one of the largest impact basins in the solar system, created when a huge asteroid hit the planet. It's called Hellas Basin, and it might once have contained an ice-covered lake.
Hellas measures 1400 miles across, so it's bigger than Texas. It's deep, too -- several miles below the equivalent of sea level.
Four billion years ago, when Hellas formed, Mars had a thicker atmosphere, and the planet was probably warmer and wetter. If Hellas filled with water, the lake would have been larger than any on present-day Earth.
As evidence for such a lake, scientists cite two channels east of Hellas that probably were carved by flowing water. These channels fed into Hellas, and probably carried water into the basin.
Mars may have been so cold that the lake was covered with ice. But it's possible that life gained a foothold beneath the ice. So Hellas Basin preserves not only a record of our solar system's violent past -- but also signs that, billions of years ago, the Red Planet was a friendlier place for life.
Script by Ken Croswell, Copyright 2009
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