The lower slopes of Mount Sharp can be seen at the top of this image, taken on July 9. Also visible are the turret of tools at the end of Curiosity's robotic arm and the rover's rock-sampling drill (lower left). NASA/JPL-Caltech

The rover's main science target, Mount Sharp, looms in the distance in this photo, taken shortly after Curiosity landed. The peak is 3.4 miles high, taller than Mount Whitney in California. NASA/JPL-Caltech

This photo, taken by a camera aboard NASA's Mars Reconnaissance Orbiter on June 27, shows Curiosity as a bluish dot near the lower right corner of the frame. Also visible are Rover's tracks. NASA/JPL-Caltech/Univ. of Arizona

A close-up view, taken on June 13, 2013, of rocks with holes that appear to contain material different from the main rock. NASA scientists are very curious about what this finer-grained, slightly darker material could be. NASA/JPL-Caltech/MSSS

A patch of rock cleaned by the rover's Dust Removal Tool, the first time the tool was deployed, Jan. 6, 2013. NASA/JPL-Caltech/MSSS

This full-circle view combines nearly 900 images taken by Curiosity, creating a virtual panorama of the Martian surface. The rover used three cameras to take the images on several different days between Oct. 5 and Nov. 16, 2012. NASA/JPL-Caltech/MSSS

This image, taken at the "Sheepbed" locality on Dec. 13, 2012, shows well-defined veins filled with whitish minerals, interpreted as calcium sulfate. The veins form when water circulates through a fracture, depositing minerals along the sides of the fracture. NASA/JPL-Caltech/MSSS

A map showing Curiosity's progress as of Aug. 1, 2013, almost a full year since it landed on Mars. NASA/JPL-Caltech/Univ. of Arizona

A self-portrait of NASA's Mars rover Curiosity combines dozens of exposures taken by its Mars Hand Lens Imager on one day in February and one in May 2013. The image also shows gray powder and two holes where Curiosity used its drill on the rock target "John Klein." NASA/JPL-Caltech/MSSS

Scientists have discovered that soil on Mars contains about 2 percent water, according to research being hailed as a major breakthrough in the quest to discover if the red planet is, or ever has been, habitable for living organisms.

A paper published today in the journal Science confirms earlier studies finding that ice is present under the Martian surface -- and the new report goes further, concluding that water can be extracted from soil samples.

It is the latest discovery using the Mars Science Laboratory mission’s Curiosity rover, which was launched from Cape Canaveral in 2011 and touched down on Mars’ Gale Crater in August 2012. The rover is tasked, in part, with finding out if Mars has ever hosted life.

Part of that mission entails looking for organic compounds in Martian soil. Curiosity -- a vehicle about the size of a Mini Cooper car, according to NASA’s website -- is equipped with 17 cameras and a robotic arm that allows it to collect and analyze soil samples, among other things.

The research published Thursday is among five different studies scientists have conducted with Curiosity and is based on results from the rover’s first-ever solid soil analysis. Curiosity collected a scoop of Martian soil into its belly and sieved it a bit at a time.

The rover used a microwave-oven-size instrument called SAM, for Sample Analysis at Mars, to heat the soil to about 815 degrees C (1,500 degrees F) to see what kinds of gases it released and get an idea of its composition.

What the scientists found was that the soil, when it reached a temperature between 200 and 300 C, was made up of about 2 percent water -- “which is kind of a lot,” according to Laurie Leshin, dean of the School of Science at Rensselaer Polytechnic Institute and lead author of the study.

The numbers mean that a cubic foot of Martian soil would have a few pints of water chemically bound into it.

“It’s likely that if astronauts went to Mars, anywhere you go, the dirt beneath your feet contains water that you could get out pretty easily,” Leshin said in a telephone interview.

Previous analyses of Martian soil by the Viking landers, as well as by the Pathfinder and the Spirit and Opportunity rovers, have shown that the soil’s chemical composition is relatively constant at different locations on the planet, so “the finer-grained fractions, in particular, may provide information about the average composition of the Martian crust,” the authors wrote in the study.

Martian water might not be immediately drinkable for humans, however. Curiosity also found in the planet’s soil a chemical called perchlorate, which can damage the proper functioning of the human thyroid. The chemical made up only about 0.5 percent of the soil sample, but as Leshin said, “This is why we send robotic explorers first, so we can understand the lay of the land … and understand what risks are there to be managed.”

This is not the first time scientists have found water or evidence of water on Mars. In 2004, the Mars Opportunity rover found minerals in the soil that are usually present only when water is, too. The shape and size of the layered rock formations were another indication that water had once been there.

And in 2008, the robotic arm of the Phoenix Mars lander dug into Martian soil and discovered the presence of ice.

Still, as Leshin says, this discovery is significant because "this is the best bulk measurement of water that we’ve done in any of the dirt."

Leshin, who previously held various roles at NASA planning human space missions, used an instrument similar to SAM back when she was a graduate student at the California Institute of Technology. In what she calls “a tiny little lab under the stairs,” she was heating up samples of rocks and analyzing their contents.

“Now we’re literally doing the same thing” on Mars, she said.

So what’s next for Curiosity? The rover will head toward the base of Mount Sharp, traveling at a rate of about 100 yards a day. When it arrives in a few months, Curiosity will drill into and examine the layers of rock there, looking for more clues.

“We’re just waiting to see what the planet wants to tell us about it,” Leshin said.