By Amina Khan, Los Angeles Times (TNS)
Where there’s brine, there’s water.
Scientists scouring the Red Planet using NASA’S Mars Reconnaissance Orbiter say they’ve found direct chemical evidence of transient saltwater flowing on the surface today.
Granted, they haven’t caught the liquid in the act — and what they’ve detected looks less like salty water and more like watery salt. But nonetheless, the discovery published by the journal Nature Geoscience helps solve a long-standing Martian mystery and sheds light on the potential for life on our nearest planetary neighbor.
“This is the first time we’ve found flowing water on a planet that’s not ours,” said lead author Lujendra Ojha, a planetary scientist and Ph.D. candidate at Georgia Tech.
Scientists got a tantalizing hint that there could be liquid water on the surface back in 2011, when Alfred McEwen, lead scientist for the Mars Reconnaissance Orbiter’s HiRISE camera, along with Ojha and other colleagues, discovered these strange dark streaks on Martian slopes that seem to grow and fade with the seasons. These “recurring slope lineae,” which can stretch up to a few meters, extend downward when it gets warm and then later shrink and fade, reappearing each Martian year.
“Ever since the discovery in 2011 … a number of us have been incredibly excited by the prospect of liquid water on Mars,” said Bethany Ehlmann, a planetary geologist at Caltech who was not involved in the paper. Nonetheless, she added, “we try to be cautious — it’s a big thing to say there’s liquid water on Mars today.”
Granted, Mars’ atmosphere is cold and thin — which means that any pure water that made it to the surface would either freeze or immediately evaporate, depending on the temperature. But a recent study by scientists using NASA’s Curiosity rover found that water might indeed be able to exist briefly on the surface — provided there were enough salts, such as perchlorates, dissolved in the liquid. These salts would keep the water from freezing or evaporating quite as easily and could actually serve to suck moisture back out of the air.
So could liquid water — very salty, briny water — really explain these strange dark streaks on Martian slopes?
Theoretically, the scientists could look for water by using the orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars, or CRISM. CRISM can look for different chemicals in a given spot on the surface by studying the telltale signature of dark bands they’ve left in the light. The problem is, it’s hard to check the light’s chemical fingerprint at the recurring slope lineae, or RSL, because, according to the study, “few locations exist in which RSL are wide or dense enough to fill even a single CRISM pixel.”
So researchers used a method where they focused on the handful of individual pixels that were mostly filled by the recurring slope lineae. They looked at four different spots with recurring slope lineae and discovered a strong fingerprint for hydrated salts — salts with water locked into the mineral structure, a clear sign that saltwater likely had flowed there. The hydrated salts included magnesium perchlorate, magnesium chlorate and sodium perchlorate.
The findings may further whet the appetite of astrobiologists looking to probe past habitable environments on the Red Planet, researchers said.
“I think it’s incredibly exciting, because when we look back at the broad scope of Mars history, it’s always in the past where there’s evidence for the most water,” Ehlmann said. “But if there’s liquid water even today, when Mars is supposedly at its driest … I think that says that there was probably liquid water for all of the last 4.5 billion years, just like there was on Earth. Not in the same quantity, but at least ephemerally, episodically, it’s there.”
Still, the water is so incredibly briny that it’s difficult to imagine microbes being able to survive with the harsh fluid.
In the meantime, where exactly the water comes from, how it’s released, and how it gets back into the soil to repeat the cycle every year remain open questions, the scientists said. Such questions could be answered by a future orbiting mission to Mars, Ehlmann added.
(c)2015 Los Angeles Times. Distributed by Tribune Content Agency, LLC.
Portions of the Martian surface shot by NASA’s Mars Reconnaissance Orbiter show many channels from 1 meter to 10 meters wide on a scarp in the Hellas impact basin, in this photograph taken January 14, 2011 and released by NASA March 9, 2011. REUTERS/NASA/JPL-Caltech/Univ. of Arizona/Handout