SETI Institute NAI team reports findings on Martian carbonates that reveal potential habitable environments on early Mars

The fate of water on Mars has been hotly debated by scientists because the planet is currently dry and cold, in contrast to the widespread fluvial features that carve much of the planet’s surface. Scientists believe that if water did once flow on the surface of Mars, the planet’s bedrock should be full of carbonates and clays. Such minerals could provide further evidence that Mars once hosted habitable environments with liquid water. Researchers have struggled to find physical evidence for carbonate-rich bedrock, which may have formed when paleoatmospheric carbon dioxide was trapped in ancient surface waters.

A new study by Wray et al. provides evidence for widespread buried deposits of Fe- and Ca-rich carbonates on Mars. The researchers, supported by the SETI Institute NASA Astrobiology Institute (NAI) team, identified carbonates on the planet using data from CRISM and HiRISE on the Mars Reconnaissance Orbiter.

“Outcrops in the 450-km wide Huygens basin contain both iron- and calcium-rich carbonate-bearing rocks” according to study lead Dr. James Wray of Georgia Tech and NAI team Co-Investigator. The Huygens basin is an ideal site to investigate carbonates because multiple impact craters and troughs expose ancient, subsurface materials where carbonates are detected across a broad region. The study highlights evidence of carbonate-bearing rocks in multiple sites across the Red Planet, including Lucaya crater, where the ancient 3.8 Ga year old carbonates and clays were buried by as much as 5 km of lava and caprock. Study co-author Dr. Janice Bishop of the SETI Institute and also a NAI Co-Investigator says that “identification of these ancient carbonates and clays on Mars represents a window into the past when the climate on Mars was very different from the cold and dry desert of today”. The extent of the global distribution of Martian carbonates is not yet resolved and the early climate on Mars remains under debate. However, this study moves us forward in our understanding of potential Martian habitability.

Aeolian bed forms overlie ancient layered, ridged carbonate-rich outcrop exposed in the central pit of Lucaya crater, northwest Huygens basin, Mars. The image was taken by the High Resolution Imaging Science Experiment (HiRISE) instrument aboard the Mars Reconnaissance Orbiter. Credit: NASA/JPL/University of Arizona.

Martian Carbonates Spotted by the Orbiter

The minerals identified by the Mars Reconnaissance Orbiter provide more evidence that the planet may have once been habitable.

The search for life on Mars has been fueled by findings that suggest the Red Planet may have once been a wet one, with ancient lakes, rivers, and oceans flowing over its surface. Where there is water, there can be life, if Earth is any example. Scientists believe that if water did once flow on the surface of Mars, the planet’s bedrock should be full of carbonates—minerals that would have formed when paleoatmospheric carbon dioxide was trapped in ancient surface waters. Such minerals could provide further evidence that Mars was once host to habitable, watery environments, but researchers have struggled to find physical evidence for a carbonate-rich bedrock.

Now Wray et al. provide new evidence for the existence of buried deposits of iron- and calcium-rich Martian carbonates. The researchers identified carbonates on the planet with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard the Mars Reconnaissance Orbiter. The tool picks up on the unique spectral signatures carbonate ions give off during vibrational transitions. The team paired CRISM data with images from the High Resolution Imaging Science Experiment (HiRISE) and Context Camera (CTX) on the orbiter and the Mars Orbiter Laser Altimeter (MOLA) on the Mars Global Surveyor to gain insights into the geologic features associated with carbonate-bearing rocks.

The researchers detected iron- and calcium-rich carbonate-bearing rocks in the Huygens basin, a basin greater than 450 kilometers wide that is rimmed with impact craters and troughs that expose ancient, subsurface materials. The widespread detection of carbonate-bearing rocks in the basin suggests that at least regionally, conditions were once suitable for carbonate formation.

The strong carbonate signals in impact craters such as the Lucaya crater suggest that the minerals may have been previously buried up to 5 kilometers below the surface in ancient rock more than 3.8 gigayears old. Thus, they represent a window into a time when the climate on Mars was very different than today. The depth and age of these rocks may partially explain why researchers failed to find large areas of carbonate-loaded bedrock in the past. Without a plate tectonic system like that of Earth to push buried materials to the surface, impacts may be one of the only ways to excavate deposits of carbonate-rich rocks.

The global distribution of Martian carbonates has yet to be resolved. Still, the authors note, the ancient carbonates could serve as a point of comparison for organics found on Mars in order to identify biosignatures of ancient life on the Red Planet. (Journal of Geophysical Research: Planets, doi:10.1002/2015JE004972, 2016)

—Kate Wheeling, Freelance Writer

Citation: Wheeling, K. (2016), Martian carbonates spotted by the Orbiter, Eos, 97, doi:10.1029/2016EO051551. Published on 3 May 2016.

Ancient layered clay-bearing bedrock (top left) and carbonate bedrock (bottom right) are exposed in the central uplift of an unnamed crater approximately 42 kilometers in diameter in eastern Hesperia Planum, Mars. The image was taken by the High Resolution Imaging Science Experiment (HiRISE) instrument aboard the Mars Reconnaissance Orbiter. Credit: NASA/JPL/University of Arizona.