In the first inventory of minerals on another planet, NASA's Mars rover Curiosity found soil that bears a striking resemblance to weathered, volcanic sand in Hawaii, scientists say.
The rover uses an X-ray imager to reveal the atomic structures of crystals in the Martian soil, the first time the technology, known as X-ray diffraction, has been used to analyse soil beyond Earth.
"This was a 22-year journey and a magical moment for me," NASA's David Blake, lead scientist for the rover's mineralogical instrument, told reporters on Tuesday.
Curiosity found the Martian sand grains have crystals similar to basaltic soils found in volcanic regions on Earth, like Hawaii.
Scientists plan to use the information about Mars' minerals to figure out if the planet most like Earth in the solar system could have supported and preserved microbial life.
"The mineralogy of Mars' soil has been a source of conjecture until now," said Curiosity scientist David Vaniman of the Planetary Science Institute in Tucson, Arizona.
"This interest isn't just academic," he added. "Soils on planets' surfaces are a reflection of surface exposure processes and history, with information on present and past climates."
Specifically, scientists want to understand what conditions existed to allow the particular minerals to form. The first Martian soil scoop is similar to basaltic materials and comprised primarily of feldspar, pyroxene and olivine.
About half the soil is non-crystalline materials, like volcanic glass, that form from the breakdown of rocks.
Several processes can account for this weathering, including interaction with water or oxygen, similar to how rust forms on iron-metal surfaces.
Brute force, such as sandstorms or meteorite impacts, also could account for the soil's weathered components, said chemist Douglas Ming of NASA's Johnson Space Center in Houston.
The Curiosity rover landed inside a giant impact crater near the Martian equator in August for a two-year, $2.5bn mission, NASA's first astrobiology expedition since the 1970s-era Viking probes.
The rover is scouting a site where three types of rock intersect. Next year, scientists plan to drive it over to a five-kilometre mound of sediment, named Mount Sharp, rising from the floor of the crater.
"We're hopeful that once we get into the truly ancient materials on Mount Sharp, we will find minerals that suggest there was a habitable environment of some kind there. We haven't had that happen yet, but we have a lot of time left," Blake said.
While X-ray diffraction has been around for a century, using the technology on Mars required years of work to scale down refrigerator-sized equipment into something that would fit into the space of a shoe box.
The miniaturised, low-power instrument is used in the mining, oil and gas industries and is being evaluated by the US Food and Drug Administration to screen for counterfeit pharmaceuticals.