In January 2004, Spirit and Opportunity, two identical robotic rovers, entered the martian atmosphere and landed after a seven-month journey from Earth. By the time "Is There Life on Mars?" ...

"We found evidence for wind, waves, no shortage of sand—a proper, vacation-style beach," said geologist Benjamin Cardenas.

"Shorelines are great locations to look for evidence of past life." Today, Mars is a chilly desert of rock and dust — but 4 billion years ago, the planet had rivers, lakes and even oceans with ...