This week, NASA released some very interesting findings regarding water on Mars, from both the agency’s Curiosity rover and the Mars Reconnaissance Orbiter (MRO). It has been known for years that Mars did indeed have liquid water on its surface at some point; the aftermath is clearly visible all over the Red Planet’s desolate surface in the form of dried-up lake beds and river channels. On-site observations of rocks on the surface also prove the landscape was wet, with fast moving streams shaping the rocks and carving channels just like water does here on Earth. Round gravel—just like what is found at the bottom of streams here at home—is also found on Mars, and Curiosity has (again) shown that Mars could have supported life eons ago.
On Monday, Dec. 9, NASA announced that their Curiosity rover had uncovered strong evidence suggesting that an ancient 30-mile-long freshwater lake in Yellowknife Bay was indeed habitable for life as we know it. Matter of fact, it was so habitable that the liquid water in that lake (when it existed, of course) would have been drinkable. Large amounts of phyllosilicate clay minerals, which form in neutral pH water, were found in powdered rock samples analyzed by Curiosity’s SAM and CheMin instruments. Elements such as oxygen, carbon, sulfur nitrogen, hydrogen, and phosphorous have all been discovered as well at the ancient lake site, but Curiosity is still on the hunt for signatures of organic molecules.
“With this finding, we’re a significant step closer to understanding how to locate environments on Mars that can support life,” said John Grotzinger, project scientist for MSL from NASA’s Jet Propulsion Laboratory in Pasadena, California. “We know there are signs that water pooled or flowed in many other locations on Mars, and now we can be more confident that they may well have been habitable, too.”
Before Martian Armageddon occurred, the lake is believed to have existed for thousands, perhaps even tens of thousands of years before the planet’s atmosphere withered away and caused the lake to evaporate. Researchers cannot exactly date when the lake covered the landscape, but they can date how long ago Gale Crater formed: 3.5 billion years. The fact that a lake existed in the crater less than 3.5 billion years ago implies that a habitable water environment existed on the surface longer than was previously believed, which in turn would mean life had more time to evolve (if it was even present in the first place).
The question Curiosity set out to answer—”was Mars ever habitable at some point in its history”?—has been answered with a resounding yes; Curiosity has definitely found an environment that would have been habitable. Matter of fact, Curiosity determined 10 months ago that Mars was habitable, when the rover drilled into a rock and, after analyzing the minerals, discovered key chemical ingredients for life in the sample.
Now, as the team redirects Curiosity toward its ultimate destination at Mt. Sharp, the objective has changed. Curiosity is now on the hunt for the building blocks of life, searching for carbon-based organic molecules.
“Really what we’re doing is turning the corner from a mission that is dedicated to the search for habitable environments to a mission that is now dedicated to the search for that subset of habitable environments which also preserves organic carbon,” said Grotzinger. “That’s the step we need to take as we explore for evidence of life on Mars.”
Meanwhile, orbiting some 150 – 250 miles above Curiosity and the Red Planet, NASA’s Mars Reconnaissance Orbiter (MRO) is making some very interesting observations of its own. Launched in 2005, MRO has—over the last couple years—observed seasonal patterns where finger-like dark markings appear to stream down slopes along the planet’s equator. Researchers now believe these slender “streams” might actually be salty liquid water flowing down steep slopes as the spring and summer seasons heat the Martian surface.
“The equatorial surface region of Mars has been regarded as dry, free of liquid or frozen water, but we may need to rethink that,” said Alfred McEwen of the University of Arizona in Tucson, principal investigator for MRO’s High Resolution Imaging Science Experiment (HiRISE) camera. “The explanation that fits best is salty water is flowing down the slopes when the temperature rises. We still don’t have any definite identification of water at these sites, but there’s nothing that rules it out, either.”
The features, which are typically less than 16 feet wide and no longer than 4,000 feet long, appear on both north-facing and south-facing walls of steep, rocky slopes in spring and summer, then fade as the temperatures drop with the coming of winter. Five well-monitored sites displaying these seasonal features are located in Valles Marineris, which is the largest canyon system in the entire Solar System.
Dissolved salts can keep water melted at temperatures when purer water freezes, and they can slow the evaporation rate so brine can flow farther. That process would definitely explain why liquid water might be flowing on the planet’s equatorial slopes during the planet’s warm seasons, but only future observations will prove whether or not MRO is truly seeing liquid water flow down the steep rocky slopes at Mars’ mid latitudes.