The Martian rock, a form of basalt, has a composition very similar to volcanic rocks found in ocean-island settings such as Hawaii and the Azores, as well as in rift zones – regions where Earth's continents split and begin separating into separate land masses.
The rock, named Jake Matijevic for a key member of the rover engineering team who passed away shortly after Curiosity arrived on the red planet, can form in a number of ways, says Edward Stolper, provost of the California Institute of Technology in Pasadena and a member of Curiosity's science team.
On Earth, this kind of rock forms as magma cools and crystallizes under relatively high pressure and with relatively high concentrations of water dissolved in the magma, he explains, adding that when the molten leftovers erupt, they tend to erupt explosively.
The release, during volcanic eruptions, of water dissolved in magma is one pathway for water vapor – a greenhouse gas – to enrich and warm a planet's atmosphere. Indeed, Curiosity's mission aims to see if Gale Crater ever could have hosted microbial life – a prospect that would have required the presence of liquid water in the crater.
On Mars, the process that formed “Jake” is unclear.
"We have one rock," Dr. Stolper said at a briefing Thursday. Sitting on the floor of Gale Crater, where fine soils and layered, sedimentary rocks seem to be the norm, Jake appears to be an interloper, removed from its original geologic setting.
If Curiosity finds more rocks like Jake in its travels to Mt. Sharp, the crater's central summit and the rover's ultimate destination, "we'll be able to evaluate the differences between them and what processes seem to relate them," he said. But if Jake is "a one-off,” he added, “we're not going to find out the details" of how it formed.
The analysis of Jake's chemical composition comes from data gathered in late September by two tools mounted on Curiosity: ChemCam and an X-ray spectrometer on an instrument turret at the end of the rover’s seven-foot-long arm.
ChemCam, which sits atop Curiosity's mast, consists of a laser that sends a thin, pulsed beam to vaporize tiny patches of rock, each pulse generating what looks like a brief spark on the rock surface. ChemCam's mini-telescope captures the light from the sparks – light whose spectrum carries the signatures of the chemical elements the rock contains.
ChemCam examined two small areas of the football-sized rock. In one, it laid down a short track of five strike marks, each about a third of a millimeter across. In the second, the laser put down a grid of nine spots. Each got 30 pulses – the first four of which clear the rock surface of dust.
The X-ray spectrometer, known as APXS, uses a radioactive source to expose the rock sample in question to X-rays. When the X-rays interact with atoms in the rock, those atoms release X-rays of their own, which carry the element's signature. APXS detects these back-atchya X-rays to tease out information about the sample's composition.
Each instrument detects some chemical elements better than others, but together, they form a powerful team while crosschecking each other's results. The time spent zapping Jake was APXS's first live-fire exercise on Mars and the first time the two were used to analyze the same rock.
Because other rovers and landers have carried X-ray spectrometers, researchers were able to determine that Jake was unique among the basaltic rocks scientists have analyzed so far on the red planet.
While researchers analyzed the results from Jake, engineers have started to clean out the hardware needed to feed rock and soil samples into two key instruments housed in Curiosity's chassis. On Mars, it seems, clean hardware is dusty hardware.
Essentially, engineers used Martian soil scooped, vibrated, and sieved, to clean unavoidable terrestrial residue from the inside walls of the sample-delivery system.
"We don't want to measure something we brought with us, we want to measure something that came from Mars," says Luther Beegle, the rover's sampling-system scientist as NASA's Jet Propulsion Laboratory in Pasadena.
The way to tell that the scrub-down is working? Dust clings to the inside surfaces of the sample-delivery system, known as CHIMRA.
Where else but on Mars would a custodian's nightmare turn into an engineer’s dream?