How did Mars get its water?

NASA scientists say that questions about the origin of water on Mars are among the many unsolved mysteries of the Red Planet.

Mars has been on a bit of a press junket the past couple of weeks. But instead of promoting a blockbuster movie, the Red Planet is settling a centuries-old debate: Is there liquid water on Mars?

A new study from NASA's Mars Science Laboratory and the team operating the Curiosity rover – which has been gathering data on Mars since it landed three years ago – confirmed that the planet, billions of years ago, had lakes of water over an extended period of time.

"Observations from the rover suggest that a series of long-lived streams and lakes existed at some point between about 3.8 to 3.3 billion years ago,” said Ashwin Vasavada, Mars Science Laboratory project scientist at NASA's Jet Propulsion Laboratory in Pasadena, California, and co-author of the new Science article (paywall) published Friday, adding that the presence of water long ago allowed sediment, “delivered” by rivers and lakes, to slowly build the lower layers of Mount Sharp, the central peak located in Gale Crater, where the Curiosity rover is focusing its data-mining.

Two millennia after Babylonians first spotted Mars moving against the backdrop of stars, theologian and scientist William Whewell concluded in 1854, with little evidence, that Mars had green seas and red land, and wondered if there might be life there.

The findings published Friday support the idea of Martian life, and confirm the conjecture about a year ago by NASA that ancient lakes may be found on Mars, and add to the developing story of a watery Mars. Last month, NASA scientists confirmed that water currently flows on Mars.

"What we thought we knew about water on Mars is constantly being put to the test,” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program at NASA Headquarters in Washington. "It’s clear that the Mars of billions of years ago more closely resembled Earth than it does today. Our challenge is to figure out how this more clement Mars was even possible, and what happened to that wetter Mars."  

Prior to Curiosity landing on Mars in 2012, scientists had already postulated that Gale Crater had been filled with layers of sediments. Some hypotheses were "dry," suggesting that sediment accumulated from wind-blown dust and sand, according to NASA. Others held firm to the possibility that layers of sediment were created in ancient lakes.

The latest data from Curiosity indicate that the wet theories were indeed correct for the lower portions of Mount Sharp. Based on the new analysis, the filling of at least the bottom layers of the mountain was caused mostly by ancient rivers and lakes over a period of less than 500 million years, NASA reports, with evidence in the geology of fast-moving streams, and the possibility that those streams emptied into bodies of standing water.

Still unknown is the original source of the water. For flowing water to have existed on the surface, Mars must have had a thicker atmosphere and warmer climate than has been theorized for the ancient era when Gale Crater experienced the intense geological activity, according to NASA.

Some of the water may have been supplied to the lakes by snowfall and rain in the highlands of the Gale Crater rim, the space agency theorizes, but scientific models have so far only maintained the mystery.

"We have tended to think of Mars as being simple," said John Grotzinger, the lead author of the new research. "We once thought of the Earth as being simple too. But the more you look into it, questions come up because you're beginning to fathom the real complexity of what we see on Mars. This is a good time to go back to reevaluate all our assumptions. Something is missing somewhere."