RSL activity in the central peaks of Horowitz crater and associated CRISM spectra. Credit: Lujendra Ojha, et al./Nature Geoscience

RSL activity in the central peaks of Horowitz crater and associated CRISM spectra.
Credit: Lujendra Ojha, et al./Nature Geoscience

Mars researchers offered today the strongest proof yet that there is “intermittent flowing liquid water” present on the Red Planet.

That prospect bolsters the chance that Mars may well be an extraterrestrial address for life. Furthermore, it offers future human explorers sites to look for Martian life and might help expeditionary crews sustain their presence on the planet.

RSL emanating from a central peak in Hale crater. Credit: Lujendra Ojha, et al./Nature Geoscience

RSL emanating from a central peak in Hale crater.
Credit: Lujendra Ojha, et al./Nature Geoscience

The new evidence comes from work led by Lujendra Ojha of the Georgia Institute of Technology. A group of experts made use of instruments onboard NASA’s Mars Reconnaissance Orbiter (MRO): the High Resolution Imaging Science Experiment (HiRISE) and the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM).

Focus of attention: RSL

The focus of attention for the orbiting gear was recurring slope lineae or RSL for Mars short-hand.

RSL form and snake down steep slopes on the planet during warm seasons when temperatures exceed -10 degrees Fahrenheit (-23 degrees Celsius). They disappear at colder times during the Martian year.

Measured were spectral signatures of hydrated minerals on slopes where the puzzling RSL are found on Mars.

Ojha reported today that spectral signatures of hydrated salts were visible in many RSL if they were relatively wide in diameter. The clincher came when the researchers looked at the same locations when RSL weren’t visible and the hydration signatures had disappeared.

Briny, rather than pure

“Something is hydrating these salts, and it appears to be these streaks that come and go with the seasons,” Ojha stated in a university press release.

Credit: Georgia Institute of Technology

Credit: Georgia Institute of Technology

“This means the water on Mars is briny, rather than pure. It makes sense because salts lower the freezing point of water. Even if RSL are slightly underground, where it’s even colder than the surface temperature, the salts would keep the water in a liquid form and allow it to creep down Martian slopes,” Ojha explains.

The researchers believe that the signatures are caused by previously discovered hydrated minerals called perchlorates. This new study, however, detected perchlorates in entirely different areas from where earlier landers explored. This is also the first time perchlorates have been identified from orbit.

NASA Mars Reconnaissance Orbiter’s HiRISE image of recurring slope lineae in Melas Chasma, Valles Marineris. Arrows point out tops and bottoms of a few lineae. Credit: NASA/JPL-Caltech/University of Arizona

NASA Mars Reconnaissance Orbiter’s HiRISE image of recurring slope lineae in Melas Chasma, Valles Marineris. Arrows point out tops and bottoms of a few lineae.
Credit: NASA/JPL-Caltech/University of Arizona

 

“This is the first spectral detection that unambiguously supports our liquid water-formation hypotheses for RSL,” Ojha adds.

Contemporary Mars

The Mars RSL team also includes researchers from NASA Ames Research Center, the Johns Hopkins University Applied Physics Laboratory, University of Arizona, Southwest Research Institute and Laboratoire de Planétologie et Géodynamique.

Their collective work appears in the paper, “Spectral evidence for hydrated salts in recurring slope lineae on Mars,” published in the journal Nature Geoscience.

“Determining whether liquid water exists on the Martian surface is central to understanding the hydrologic cycle and potential for extant life on Mars,” they write in the research paper.

“These results strongly support the hypothesis that seasonal warm slopes are forming liquid water on contemporary Mars. The spectral identification of perchlorate in association with RSL also suggests that the water is briny rather than pure,” the paper notes.

Credit: Georgia Institute of Technology

Credit: Georgia Institute of Technology

Additionally, the paper calls for “further astrobiological characterization and exploration of these unique regions on Mars.” However, the scientists do caution that while there are transiently wet conditions near surface on Mars, the water activity in perchlorate solutions “may be too low to support known terrestrial life.”

What next?

So given this new research, what next?

James Wray, Georgia Tech assistant professor and advisor to the university-led work, told Inside Outer Space:

“Personally, I think we could learn a lot about RSL from landing ‘near’ them…far enough away that they’re outside the landing uncertainty ellipse…and then driving close enough to image, but not to touch.”

Wray said that from orbit there’s no way to watch a given RSL evolve from one hour to the next, day after day, to determine when they are active.

“We could do this easily on the ground, even from a stationary lander,” Wray said. “Of course, eventually we will want to know more about their chemistry and organic content, if any, which would likely require contact science using a sterilized probe.”

RSL exploration zone. THEMIS daytime-IR mosaic with proposed human survey zone (blue circle) and features of interest. Credit: A. McEwen, et al.

RSL exploration zone. THEMIS daytime-IR mosaic with proposed human survey zone (blue circle) and features of interest.
Credit: A. McEwen, et al.

Human exploration sites

Next month, the “First Landing Site/Exploration Zone Workshop for Human Missions to the Surface of Mars” is being held at the Lunar and Planetary Institute in Houston, Texas.

One favorable zone advocated for human exploration is Eastern Melas Chasm. In work spearheaded by Alfred McEwen at the University of Arizona, that locale meets a number of criteria, including access to RSL.

Still to be determined, however, is whether or not RSL can produce useable water for human crews, McEwen and his colleagues explain. If Eastern Melas is considered a promising region for astronauts to inspect, then more CRISM and HIRISE coverage by MRO is warranted. A future orbiter could provide important new observations as well, they suggest.

Major priority

Similarly, Hale crater is being proposed, primarily because of the ease with which liquid water can be extracted from recurring slope lineae found on the slopes of its central peak complex.

According to lead author of that exploration zone paper, David Stillman of the Southwest Research Institute in Boulder, Colorado: “The search for extant life within RSL should be a major priority.”

Proposed Hale crater site for human exploration. Credit: D.E. Stillman, et al.

Proposed Hale crater site for human exploration.
Credit: D.E. Stillman, et al.

Stillman notes that the RSL in Hale crater must be so briny – very low water activity values — that no known terrestrial life can respire there. This reduces the impact of cross-contamination by terrestrial life, he and colleagues suggest, therefore that reduces planetary protection worries.

“However, Martian life may have either evolved a way to live in such an environment, or may be living within the depths of the RSL source regions,” Stillman and his co-authors conclude.

 

For more information, go to:

Mineralogical Confirmation for Liquid Water on Present-day Mars

http://www.news.gatech.edu/2015/09/25/mineralogical-confirmation-liquid-water-present-day-mars

Also, go to the Nature Geoscience Letter:

“Spectral evidence for hydrated salts in recurring slope lineae on Mars”

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2546.html

 

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