On January 3, Spirit, NASA's 400-pound rover, landed on what may be a dried-up lake bed on Mars. "There's not much doubt: this site contained a body of liquid water, at least for some amount of time," says Jim Garvin, NASA's Lead Scientist for Mars Exploration.
The site is Gusev Crater, a 90-mile wide hole in the ground that probably formed three to four billion years ago when an asteroid crashed just south of Mars' equator. There's a channel system that drains into it, which probably carried liquid water, or water and ice, into the crater. "It's hard to imagine the landscape looking this way unless water was somehow involved," adds Garvin.
Right: A Mars Global Surveyor image of Gusev Crater. The arrow indicates the direction of possible water flow into the crater. [More]
Right now, inside the crater, researchers expect to find sediments, which may be nearly 3,000 feet thick. These sediments, which, researchers hope were deposited by water, may have been covered by dust and sand that's blown into the crater over the past two billion years.
But if there was once water in Gusev, its signature should still be there.
Water, of course, is important because it could signal an environment once-friendly to life. The landscape seen from orbit is very persuasive. But, Garvin says, researchers can't be certain that Gusev contained liquid water until they examine the site up close.
"The Gusev landscape we see today could have been modified by lava, ice, and winds," he notes. "Aspects of it could have been formed by standing water, or by intermittent floods." Spirit carries a suite of tools that will find out.
The rover will be able to grind away the surface cover on rocks and analyze minerals inside. It will be able to view its surroundings with unprecedented detail and precision. It can scoot over to the most interesting rocks it finds in order to examine them more closely.
With these tools and others, Spirit will work to find out what really happened.
One clear sign of past water will be in the rocks. For example, if indeed Gusev once held a giant lake (more than 10 times the size of the famous Crater Lake here in the US) certain key minerals are likely to be found in its rocks. Spirit might find evaporites--minerals formed as water dries up. Salt or gypsum are familiar ones here on Earth. Salt's component parts--sodium and chloride--are separated, dissolved in sea water, but as the water dries up, the sodium and chloride join together to form the mineral "halite."
Above: An artist's concept of the Mars rover Spirit approaching an interesting rock. [More]
On Mars, Spirit might find evaporites like gypsum, or calcium magnesian sulfate. It might also find minerals involving carbonates (i.e., calcium carbonate). These are sometimes, although not always, produced by or from living organisms. But they are almost always a sign of water--"at least here on Earth," notes Garvin.
Another sign will be in the way the sediments are organized. For example, if the sediments were blown in by winds, the layers may be more erratic, to reflect the changing directions of airflow (as in fossil dunes here on Earth). If they were deposited by water, they are more likely to be layered evenly, one on top of the other in rhythmic stacks.
The most exciting result, says Garvin, would be proving that liquid water existed at the surface of this site for a long time. "Persistent standing bodies of water are possible habitats for life," he explains.
But whatever information Gusev yields will be important. Water or not. Life or not. Whatever it tells us will help determine the course of future explorations on Mars.
Mars Exploration -- (JPL) NASA's home page for exploration of the red planet
Carbonated Mars -- (Science@NASA) Here on Earth the only way to make carbonate rocks is with the aid of liquid water. Finding such rocks on Mars might prove, once and for all, that the barren Red Planet was once warm and wet.
The Case of the Missing Mars Water -- (Science@NASA) Plenty of clues suggest that liquid water once flowed on Mars --raising hopes that life could have arisen there-- but the evidence remains inconclusive and sometimes contradictory
Making a Splash on Mars -- (Science@NASA) On a planet that's colder than Antarctica and where water boils at ten degrees above freezing, how could liquid water ever exist? Scientists say a dash of salt might help.
Sedimentary Mars -- (Science@NASA) Mars Global Surveyor images reveal sedimentary rock layers on the Red Planet that may have formed
Layers of Mars -- (Science@NASA) Mars Global Surveyor has spotted terrains on Mars that look like sedimentary rock deposits. If the mysterious layers formed underwater, as some scientists suspect, they may be a good place to hunt for Martian fossils.