Water on Mars more acidic than previously thought

A new Martian sample taken by NASA's Curiosity rover hints at water that was more acidic than evidenced in its first drill at Mount Sharp - a layered rock record of ancient Martian environment.

The rover used a new, low-percussion-level drilling technique to collect sample powder from a rock target called "Mojave 2."

The first sample of the mountain's base layer came from a target called "Confidence Hills".

"The analysis shows a significant amount of jarosite, an oxidised mineral containing iron and sulfur that forms in acidic environments," NASA said in a statement.

"Our initial assessment of the newest sample indicates that it has much more jarosite than Confidence Hills," said David Vaniman, deputy principal investigator of the Planetary Science Institute, Tucson, Arizona.

The minerals in "Confidence Hills" indicate less acidic conditions of formation.

Curiosity reached the base of Mount Sharp five months ago after two years of examining other sites inside Gale Crater and driving toward the mountain at the crater's centre.

Both target sites lie in a outcrop called "Pahrump Hills," an exposure of the Murray formation that is the basal geological unit of Mount Sharp.

The Curiosity mission team has already proposed a hypothesis that this mountain, the size of Mount Rainier in Washington, began as sediments deposited in a series of lakes filling and drying.

The team chose a target called "Mojave" largely due to an abundance of slender features, slightly smaller than rice grains, visible on the rock surface.

Researchers sought to determine whether these are salt-mineral crystals, such as those that could result from evaporation of a drying lake, or if they have some other composition.

Mojave 2, an alternative drilling target selected at the Mojave site, has the same type of crystal-shaped features.

"This was our first use of low-percussion drilling on Mars, designed to reduce the energy we impart to the rock," said John Michael Morookian, the team's surface science and sampling activity lead for the Pahrump Hills campaign.