(Sen) - When Mars Curiosity fired radioactive particles at a rock for the first time, it was supposed to be a calibration – a way for scientists to ensure that an instrument on the £1.3 billion (US$2.1 billion) rover was working correctly.
Not only is Curiosity's Alpha Particle X-Ray Spectrometer in fine shape, but the rover also made a surprising finding with it: Curiosity discovered a type of igneous rock never seen before on Mars.
Results from the APXS and another instrument, presented to reporters Thursday, show that the rock is an alkaline basalt. It's a rare kind of rock on Earth, but the type is well-studied.
On Earth, this type of rock is formed when water-rich magma crystallizes at high pressure. Scientists are not sure exactly where alkaline basalts originate, but theories are that perhaps it comes from oceanic crust, or water-enriched rocks found on the Earth's lithosphere (crust and upper mantle). How the process works on Mars is unknown, scientists cautioned.
"It was a bit of a surprise, what we found," said Ralf Gellert, the principal investigator for Curiosity's APXS instrument, in a conference call with reporters.
Specifically, NASA found that the rock is high in elements such as sodium, alumnium, silicon and potassium - called "feldspar" minerals. It also has little magnesium and iron in it, which are elements that have been found commonly in other Martian landing sites.
It's not known how old the rock is or where exactly it came from.
Edward Stolper, a co-investigator on the Curiosity science team, compared the rock's formation to how applejack liquor is made.
"You take hard cider, and the way it was made in colonial times, they would put it in big barrels in the winter. It would freeze, but not fully," he explained.
Mars Curiosity makes a footprint in the Martian soil. Credit: NASA/JPL-Caltech
As the cider crystallized, the pioneers would remove the ice from the top of the barrel, leaving the unfrozen alcohol behind.
On a planet, Stolper explained, a similar process happens when you generate water-rich magma. It melts on the interior of the Earth, then crystallizes as it cools, "just like the liquid applejack."
The rock was also analyzed with a laser from Curiosity's chemical camera. ChemCam has been used on about 30 rocks already, but this was the first time scientists could compare its findings with that of APXS.
Additionally, Curiosity picked up its first handful of Martian soil on Mars and put it into the rover for further analysis. The rover has a laboratory inside of it that, as an example, can sniff the gases from Martian rocks to get a sense of their composition.