Gray cuttings from Curiosity's drilling into a target called "Mojave 2" are visible surrounding the sample-collection hole in this Jan. 31, 2015, image from the rover's MAHLI camera. This site in the "Pahrump Hills" outcrop provided the mission's second drilled sample of Mars' Mount Sharp. Credit: NASA/JPL-Caltech/MSSS

Curiosity Drilling on Mars Reveals Ancient Acidic Conditions But No Mineral Traces

The second drilling on Martian mountain surface by NASA’s Curiosity Mars rover hints at ancient effects of water that was more acidic than any evidenced in the rover’s first taste of Mount Sharp, said NASA.

The Curiosity 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 toward the mountain at the crater’s center. The first sample of the mountain’s base layer came from a target called “Confidence Hills,” drilled in September.

NASA's curisoity Rover is all set to dig for crystals in rock on evaporated lake in Gale crater on Mars.(Photo: NASA)

NASA’s curisoity Rover is all set to dig for crystals in rock on evaporated lake in Gale crater on Mars.(Photo: NASA)

A preliminary check of the minerals in the Mojave 2 sample comes from analyzing it with the Chemistry and Mineralogy (CheMin) instrument inside Curiosity. The still-partial analysis shows a significant amount of jarosite, an oxidized mineral containing iron and sulfur 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.

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.

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-ton 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. One goal was to select which targets, if any, to drill for samples to be delivered into the rover’s internal analytical instruments.

The preliminary look at CheMin data from the drilled sample material did not identify any mineral source, said NASA. Possibly, minerals that originally formed the crystals may have been replaced by other minerals during later periods of wet environmental conditions, it added.

The drilling to collect Mojave 2 sample material might not have succeeded if the rover team had not recently expanded its options for operating the drill.

“This was our first use of low-percussion drilling on Mars, designed to reduce the energy we impart to the rock,” said JPL’s John Michael Morookian, the team’s surface science and sampling activity lead for the Pahrump Hills campaign. “Curiosity’s drill is essentially a hammer and chisel, and this gives us a way not to hammer as hard.”

NASA’s Mars Science Laboratory Project is using Curiosity to assess ancient habitable environments and major changes in Martian environmental conditions. JPL, a division of the California Institute of Technology in Pasadena, which has built the rover is managing the project for NASA’s Science Mission Directorate in Washington.

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