Water on Mars: A Brief (and Extremely Long) History

The surface of Mars, new research suggests, is 2 percent water -- yet another reminder that the Red Planet may once have been blue.

A map of a region known as Deuteronilus Mensae, in the northern hemisphere of Mars, shows the locations of ice deposits that have been detected by the Shallow Radar instrument of NASA's Mars Reconnaissance Orbiter. The deposits are depicted in blue. (NASA/JPL-Caltech/ASI/University of Rome/Southwest Research Institute)

The Curiosity rover has found water in the soil of Mars. Which is, on the one hand, big news: Water! Right in the soil of the seemingly barren planet! On the other hand, though, it's news that isn't terribly surprising: Scientists have long speculated that Mars was once Earth-like in its capacity to host water. And the planet, of course, is already known to host both ice and snow at its poles.

Still, though, the water detected in the soil (in this case, of the Gale Crater, the area the rover is exploring) is a big deal -- a confirmation of yet another way that Mars and Earth are more similar than it may appear to the naked eye. The news came via a series of five papers published in the journal Science -- the first set, The Guardian's Alok Jha notes, "of formal, peer-reviewed results from the Curiosity mission." The papers offer details of the scientific experiments Curiosity carried out during the first four months it spent tooling around on the Martian surface. And investigations into the planet's water content were among them.

How much water, actually, is present in the soil of Mars? A decent amount, it seems. According to Laurie Leshin, the dean of science at Rensselaer Polytechnic Institute and the lead author of the Science paper that confirmed the existence of water in the soil"If you took about a cubic foot of the dirt and heated it up, you'd get a couple of pints of water out of that." Which is, she notes, "a couple of water bottles' worth that you would take to the gym." (NB: Don't take Martian water to the gym.) Overall, Leshin and her colleagues estimate, the Martian soil contains about 2 percent water by weight. Which is still arid by Earth standards ... but moister than nothing. It means that if you're looking for water on Mars, as Leshin puts it, "You don't need to go to the polar caps. You don't need to dig way down deep."

So: Let's celebrate the newly detected Martian Moisture! With photos! Below, culled from Space.com's wonderfully lengthy image collection, a retrospective: Water on Mars -- as we've witnessed it, as we think it to be, and as we imagine it once was. For more, see the full (and amazing) 34-image slideshow.

This image of a slope inside Mars' Newton crater, combines orbital imagery with 3-D modeling to depict water flows that may have appeared during Martian springs and summers. (NASA/JPL-Caltech/University of Arizona)
A look at Mars's McLaughlin Crater, annotated to show the locations of minerals and clays created by water in the ancient past. Billions of years ago, the region may have been a groundwater lake. (NASA/JPL-Caltech/University of Arizona)
The HiRISE camera also imaged a gully that may have been carved by flowing water.(NASA/JPL/University of Arizona)
An artist's rendering of the ancient oceans thought to have covered ancient Mars 3 billion years ago. The image is based on the actual topography of Mars, as measured by NASA's Mars Orbiter Laser Altimeter. (G. diAchille via Space.com)
An artist's rendering of Mars as it might have appeared more than 2 billion years ago. The ocean fills the lowland basin that now occupies the north polar region. (Taylor Perron/UC Berkeley)

Update: I neglected to include, in the series above, the most detailed and definitive water-on-Mars image -- created by Ellen Roper, archived by NASA's Astronomy Picture of the Day, and sent to me by reader Paula Naughtin:

Ellen Roper via NASA/APOD