One potential landing site appears to have ridges that hint at past hydrothermal activity
UNIV. OF ARIZONA, JPL-CALTECH/NASA
Ancient hot springs may have bubbled up at a spot just south of the Martian equator. Left-behind mineral deposits described in a new study are not the first evidence of such features on Mars. But if confirmed, the discovery could affect where NASA’s Mars 2020 mission rover lands to start its hunt for signs of life.
The spot scrutinized in the new study is called Margaritifer Terra. This heavily cratered site with lots of fractures in its surface may have formed from magma or melting rock from asteroid impacts. Analysis of high-resolution images from the Mars Reconnaissance Orbiter suggests not all of the site’s features resulted from volcanic activity or heavy hits to the Martian surface. Certain ridges along fractures in one of the region’s impact craters have mineral deposits that may have come from the upwelling of water from ancient hot springs, researchers report July 15 in Geophysical Research Letters.
Hot springs hint at hydrothermal activity. “That kind of hydrothermal environment is favorable to life on Earth, and may have been so on Mars, too,” says study coauthor Rebecca Thomas of University of Colorado Boulder. Chemical-rich fluids typically flow freely at hydrothermal vents, providing energy for life in a harsh environment. This habitat, Thomas says, can also lay down sulfur- or silica-rich mineral deposits, which are good at preserving evidence of life, most likely microbes in the case of Mars.
While it is unclear what type of minerals line the ridges analyzed in the study, the team suggests that because volcanic activity was in the area, along with evidence of flowing fluids, the deposits are probably the result of hot springs and thus rich in sulfur or silica.
The potential life-bearing ridges at Margaritifer Terra are strikingly similar to features found at a site called Northeast Syrtis Major, the team says. Those ridges also could have formed from hydrothermal activity. That’s important because Northeast Syrtis Major is one of three proposed landing sites for the Mars 2020 mission. The other two sites — Jezero crater and Gusev crater, which shows hints of hot springs and where the rover Spirit explored from 2004 to 2010 — also have features that suggest they were once wet and therefore could harbor signs of life.
Northeast Syrtis Major has repeatedly been listed as a candidate landing site for rover missions because it has clays, which suggest the region once had water. The site also shows signs of ancient volcanic activity and flowing water, meaning it was warm and wet. All are solid signs for potential life. Large silica deposits near a volcano in the Syrtis Major region also hint at past hydrothermal activity. If some of the ridges in Northeast Syrtis Major craters also offer evidence of ancient hydrothermal activity, the site might have an edge over the other two for where to land the Mars 2020 rover.
The presence of hydrothermal deposits is one of the prime reasons why a return to Gusev Crater is being considered. But while hydrothermal deposits are the main benefit of Gusev Crater, Northeast Syrtis Major has the potential to reveal signatures of life from a range of environments, which were laid down over a long period of time, Thomas says.
Not everyone is convinced that the new work will influence NASA’s decision. “I don't think this will have a large implication on the Mars 2020 plans. Those finalist sites have been selected above many amazing sites over the past several years,” says J.R. Skok of the SETI Institute in Mountain View, Calif. “What this does show is how interesting, diverse and potentially habitable ancient Mars was.”
The destination for the Mars 2020 mission could be determined as early as the fall of 2018.
R.J. Thomas, S.L. Potter-McIntyre and B.M. Hynek. Large-scale fluid-deposited mineralization in Margaritifer Terra, Mars. Geophysical Research Letters. Published online July 15, 2017. doi: 10.1002/2017GL073388.