Mars Only Briefly Wet, Study Says

A new study is throwing cold water on the idea that Mars was once a warm, wet planet.

Because Mars’ surface is carved by major river channels and covered by huge lake or ocean shores, many scientists have long believed that the Red Planet was once warmer and wetter, and basked in Earth-like conditions that could have allowed the evolution of life.

But an analysis suggests that water occurred for only a short time in the early history of Mars, when the planet was being bombarded by asteroids and comets.

These impacts, which occurred about 3.5 billion years ago, probably brought with them scalding rains and higher temperatures that melted some of the ice at the planet’s poles. Such activity could have created temporary lakes and rivers. The new work, published in this week’s issue of Science, shows that Mars’ river channels are about the same age as the craters.

“We believe that through most of its history, Mars has been a cold, dry planet,” said Teresa Segura, a scientist at the University of Colorado at Boulder who conducted the study with scientists from NASA Ames Research Center. The team describes the planet’s weather as “an almost endless winter broken by episodes of scalding rains followed by flash floods.”