One of the primary science objectives of the Curiosity mission is to assess the habitability of ancient and modern martian environments. Curiosity is not searching for evidence for life, but is looking for the conditions necessary for life to survive, namely liquid water and the chemical building blocks for life. Curiosity discovered an ancient habitable environment near its landing site in a place called Yellowknife Bay. The rocks in Yellowknife Bay are made up of very fine grained sediments, indicating that they were deposited in a tranquil lake environment. Data from CheMin helped scientists identify minerals that formed in fresh water under near-neutral conditions. Data returned from SAM, the Alpha Particle X-ray Spectrometer (APXS), and the Chemistry and Camera (ChemCam) showed the presence of the chemical building blocks for life: C, H, N, O, P, and S. If life was present on Mars over 3.5 billion years ago, it could have thrived in Yellowknife Bay.
Read more about Yellowknife Bay from ARES scientists' research published in Science:
D. W. Ming et al., including P. D. Archer, Jr., B. Sutter, P. B. Niles, and R. V. Morris (2014) Volatile and organic compositions of sedimentary rocks in Yellowknife Bay, Gale crater, Mars, Science, 343, doi:10.1126/science.1245267.
D. T. Vaniman et al., including D. W. Ming, R. V. Morris, and E. B. Rampe (2014) Mineralogy of a mudstone at Yellowknife Bay, Gale crater, Mars, Science, 343, doi:10.1126/science.1243480.
Curiosity landed on the flat plains of Gale crater because it would not be safe for the rover to land on the steep slopes of Mount Sharp. For the first two years of the mission, Curiosity studied the rocks and soils on the plains as the rover drove toward Mount Sharp. Curiosity arrived at the base of Mount Sharp on September 2014 and studied the rocks in a location called the Pahrump Hills. These rocks are made up of fine-grained sediments with thin mm-scale laminations, suggesting these sediments were deposited in a lake environment. The discovery of lake sediments at Yellowknife Bay and the Pahrump Hills indicates that lake environments were persistent in ancient Gale crater. Unlike the rocks in Yellowknife Bay, the rocks of the Pahrump Hills contain some minerals that are characteristic of acidic environments, including an iron-sulfate mineral called jarosite. ARES scientists Doug Ming and Dick Morris have studied these minerals extensively on The Big Island of Hawaii and Rio Tinto, Spain. The discovery of jarosite in the Pahrump Hills may indicate that acidic, iron- and sulfate-bearing fluids moved through these sediments after they had been deposited.
Beyond the Pahrump Hills in a location called Marias Pass, Curiosity discovered rocks that were enriched in SiO2. This discovery is particularly exciting because SiO2 (or silica) can be enriched through aqueous processes from fluids depositing silica or from fluids stripping away mobile elements and leaving silica behind. Curiosity drilled a sample called Buckskin and delivered it to CheMin. In Buckskin, CheMin discovered a mineral that had never before been detected on Mars: tridymite. Tridymite is a SiO2 polymorph that forms under low pressure and high temperature (>800 °C). It is rare on Earth and is generally found in rhyolitic tuff deposits, where explosive, silicic volcanic eruptions deposited tons of hot ash. However, the rocks in Marias Pass were part of the same unit as those studied at the Pahrump Hills and were also deposited in a lake environment. It is possible that the tridymite is evidence for silicic volcanism on Mars and was eroded from a rhyolitic tuff deposit, but ARES scientists are exploring other processes that could have formed the tridymite discovered at Marias Pass.
MSL Press Releases: https://mars.nasa.gov/msl/news/whatsnew/
Raw Images from MSL Cameras: http://mars.nasa.gov/msl/multimedia/raw/
Information about CheMin: https://msl-scicorner.jpl.nasa.gov/Instruments/CheMin/
Information about SAM: https://msl-scicorner.jpl.nasa.gov/Instruments/SAM/