US: NASA’s Mars rover Spirit has found more evidence that water trickled beneath the Red Planet’s surface in the past perhaps within the last few hundred thousand years. The sandy spot where Spirit got bogged down last year harbors stratified layers of dirt with different compositions close to the surface, a new study reveals. Researchers suspect these layers were caused by seepage of thin films of water on Mars, perhaps from melting frost or snow.
This seepage could have occurred during cyclical climate changes when Mars was tilted more on its axis, researchers said. The water may have moved down into the sand, carrying soluble minerals deeper than less-soluble ones, they added.
The axis tilt of Mars varies over time scales of hundreds of thousands of years. The fact that Spirit found these layers in the dirt rather than locked away in rock further suggests the water was seeping relatively recently, rather than billions of years ago, researchers said.
“Once you freeze that evidence in a rock, it can stay there for a long time,” said Bruce Banerdt, a project scientist for the Mars Exploration Rovers project at NASA’s Jet Propulsion Laboratory in Pasadena, California. “But you don’t expect to maintain evidence in loose dirt for long periods of time.”
The new study, which appears in the Journal of Geophysical Research, is based on observations made by Spirit before it stopped communicating with Earth in March this year. The findings contribute to an accumulating set of evidence that Mars may harbour small amounts of liquid water at some periods during ongoing climate cycles.
Spirit, its rover twin Opportunity and other NASA Mars missions have found evidence of wet Martian environments billions of years ago that may have been favourable for life. Observations by the Phoenix Mars Lander in 2008 and various orbiters since 2002 have identified buried layers of water ice at high and middle latitudes and frozen water in polar ice caps.