Looking for life on Mars — in Chile
ASU scientists make discovery at South American hot springs that could spur revisiting a Red Planet location already explored
Two geoscientists at Arizona State University have made a discovery among hot springs in Chile that may spur scientists to revisit a location on Mars explored several years ago by NASA's Spirit rover. The discovery involves fingerlike structures that form in the hot spring deposits by processes that combine biological and non-biological activity.
The Chilean hot springs are at a place called El Tatio and lie at the edge of the extremely dry Atacama Desert, one of the best "Mars analog" sites on Earth.
Home Plate is a ancient and eroded volcanic ash deposit about 100 yards across that lies in Gusev Crater's Columbia Hills. At some point in the past a hot spring was active here, producing silica outcrops that appear nearly identical to features found at the El Tatio hot springs in Chile. The silica outcrops lie next to Home Plate's right edge, near the Spirit rover (circled).Photo by NASA/JPL-Caltech/University of Arizona
NASA's Spirit rover imaged this cluster of fingerlike silica nodules near Home Plate in the Columbia Hills in April 2007. The nodules appear to have the same size and shape as silica nodules at the El Tatio hot springs on Earth, where biological activity contributed to their formation.Photo by NASA/JPL-Caltech
The El Tatio hot springs in Chile give scientists the opportunity to examine hydrothermal silica deposits in a Mars-like environment. These fingerlike nodules grew with the activity of microorganisms. Their resemblance to silica deposits found at Home Plate in Gusev Crater suggests a possible target for NASA's next Mars rover, planned for launch in 2020.Photo by Steve Ruff
"We went to El Tatio looking for comparisons with the features found by Spirit at Home Plate," said Ruff. "Our results show that the conditions at El Tatio produce silica deposits with characteristics that are among the most Mars-like of any silica deposits on Earth."
These characteristics compare favorably with the Martian Home Plate silica outcrops, Ruff explained. "The fact that microbes play a role in producing the distinctive silica structures at El Tatio raises the possibility that the Martian silica structures formed in a comparable manner — in other words with the help of organisms that were alive at the time."
NASA has plans to send a new rover to Mars in 2020. The yet-unnamed rover will be similar in size and power to the Curiosity rover, currently exploring Gale Crater. But the new rover will have more advanced instruments and the ability to collect and cache samples for later retrieval.
So where should the 2020 rover go?
As NASA did with Curiosity, it has held a series of workshops over several years, where Mars scientists present their best case for one landing site or another. At the end of each workshop, candidate sites are ranked according to their fitness in regard to certain qualities. These include geological setting, potential for preserving biosignatures, and quality of returned samples.
Currently the Columbia Hills/Home Plate site in Gusev Crater stands No. 2 on the list of eight candidates. It's second only to an ancient lakebed in Jezero Crater on the northwest edge of Isidis Planitia, an old impact basin. The next site selection workshop is scheduled for February 2017, with plans to cut the list down to a "Final Four."
Although returning to Gusev's Columbia Hills and Home Plate would rule out exploring a completely new area of Mars — which many scientists would like to do — Ruff and Farmer are hopeful that the site's chances are quite good.
"This is a known hydrothermal deposit," said Ruff. "We know exactly where to land and where to go collect samples. And the silica structures found by Spirit meet the definition of a potential biosignature."