A new sample from a Martian mountain by NASA Curiosity rover hints at water that was more acidic than any evidenced in the rover's first taste of Mount Sharp, a layered rock record of ancient Martian environments.
The rover used a new, low-percussion-level drilling technique to collect sample powder last week from a rock target called "Mojave 2."
Curiosity reached the base of Mount Sharp five months ago after two years of examining other sites inside Gale Crater and driving towards the mountain at the crater's centre.
The first sample of the mountain's base layer came from a target called "Confidence Hills," drilled in September, last year.
A preliminary check of the minerals in the Mojave 2 sample comes from analysing it with the Chemistry and Mineralogy (CheMin) instrument inside Curiosity.
The still-partial analysis shows a significant amount of jarosite, an oxidised mineral containing iron and sulphur that forms in acidic environments.
"Our initial assessment of the newest sample indicates that it has much more jarosite than Confidence Hills," said CheMin Deputy Principal Investigator David Vaniman, of the Planetary Science Institute, Tucson, Arizona.
The minerals in Confidence Hills indicate less acidic conditions of formation.
Open questions include whether the more acidic water evident at Mojave 2 was part of environmental conditions when sediments building the mountain were first deposited, or fluid that soaked the site later.
The Curiosity mission team has already proposed a hypothesis that this mountain began as sediments deposited in a series of lakes filling and drying.
In the months between Curiosity's drilling of these two targets, the rover team based at NASA's Jet Propulsion Laboratory, Pasadena, California, directed the vehicle through an intensive campaign at Pahrump Hills.
The one-tonne roving laboratory zig-zagged up and down the outcrop's slope, using cameras and spectrometer instruments to study features of interest at increasing levels of detail.
