The question of whether there could still be liquid water somewhere on Mars today is one of the most debated in planetary science, and now there is new evidence that there just might be. The findings were announced today, February 10, 2014, by scientists from the Mars Reconnaissance Orbiter mission.
The new results have to do with features on the Martian surface called "recurring slope linear" (RSL), which are dark, narrow streaks on some slopes which flow downhill and can reoccur in the same locations over and over again. They tend to form during periods of warmer temperatures and look like small rivulets of water running downhill, but is that what they really are?
"We still don't have a smoking gun for existence of water in RSL, although we're not sure how this process would take place without water," said Lujendra Ojha, a graduate student at the Georgia Institute of Technology in Atlanta. He is the lead author of two new reports about the unusual flows.
In order to try and determine if these streaks are indeed water-related, Ojha and colleague James Wray examined RSLs at 13 known locations using images from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter.
While not yet finding the spectral signature of water or salts, they did find them for ferric and ferrous iron-bearing minerals. The minerals are more abundant in the slope streaks and so thought to be left over from whatever process created the streaks. Two possible explanations are related to these, and both involve water: an increase in the more-oxidized (ferric) component of the minerals, or an overall darkening due to moisture, just like you see with wet sand or dirt. It is also possible that fine dust is being removed from the surface, which could involve either a wet process or a dry one.
According to Ojha, "Just like the RSL themselves, the strength of the spectral signatures varies according to the seasons. They're stronger when it's warmer and less significant when it's colder."
As to why water itself wasn't detected yet, the spectral observations might easily miss them since the dark flows are much narrower than the area of ground sampled by CRISM.
The most likely explanation for the RSLs according to scientists though is still near-surface briny water or ice, which, during warmer periods, could leak out at the top of slopes and remain liquid long enough in the cold and thin atmosphere to flow down the slopes.
"The flow of water, even briny water, anywhere on Mars today would be a major discovery, impacting our understanding of present climate change on Mars and possibly indicating potential habitats for life near the surface on modern Mars," said Richard Zurek, Mars Reconnaissance Orbiter Project Scientist at NASA's Jet Propulsion Laboratory in Pasadena.
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