Streaks on Martian slopes, such as these depicted in a false-color view of Hale Crater, are thought to be formed by seasonal flow of water. The streaks are roughly the length of a football field. Mars photos courtesy of NASA.
When NASA confirmed the presence of liquid water flowing on Mars in September 2015, it was big news around the world. Frozen water at the planet’s poles, and ancient water that sculpted its surface, have long been known to science. But flowing water kept the door open to the possibility of finding life.
At the University of Arkansas’ Center for Space and Planetary Sciences, however, the announcement was a little anticlimactic. “It didn’t surprise us,” says center Director Larry Roe. “Much of our research in the last 10 years has been oriented toward water on Mars. We expected this to happen.”
It’s not that researchers at the center knew something NASA didn’t; in fact, they have been analyzing NASA data for a long time. It’s more that water on Mars has been an operating parameter for the center’s researchers. “We configured our research around the argument that there is water on Mars,” said Roe.
Vincent Chevrier, research assistant professor. Photo by Russell Cothren.
Origins
The center began in the fall of 2000 with a two-year, $1.6 million grant from the National Science Foundation. At the outset, it was a joint effort between the U of A and Oklahoma State University designed to create a critical mass of researchers and facilities to contribute to NASA’s ongoing program of robotic space exploration.
It has evolved into an interdisciplinary program among seven U of A departments, three colleges and the Graduate School and International Education. It performs a broad array of research and offers graduate degrees in space and planetary sciences, biology, geology and physics.
At the heart of the center is the W.M. Keck Laboratory for Planetary Simulations. There, center researchers recreate surface conditions on other worlds, then test how chemicals and compounds might react under such conditions. To date they’ve dialed up versions of Venus, Saturn’s icy moon Titan and Mars.
Center researchers also focus on astrophysics, seeking answers to questions about galaxy structure, black hole mass and binary star systems. And they work on engineering issues, including several related to small, relatively affordable research instruments called cube satellites. Once the realm of student projects, these 4-inch cubes have recently become a vehicle for serious scientific work thanks to smaller, more powerful electronics packed inside them. Researchers are working on ways to cheaply communicate with cube satellites, and pull them out of orbit after their useful life is finished.
Mars-centric
Vincent Chevrier, a research assistant professor, is the center’s point man on Mars. He has been studying the Red Planet for almost a decade. His early work on the thermodynamics of Martian clays contradicted a popular theory that the planet once had sufficient amounts of the greenhouse gas carbon dioxide to create an atmosphere warm enough for liquid water.
An ancient atmosphere rich in carbon dioxide could explain why the planet’s surface appears to be shaped by river channels and other geological formations consistent with the presence of water. But Chevrier’s calculations on clay found in Martian outcroppings that are 4.5 to 5 billion years old found none of the byproducts that should be present if the clay had formed in a carbon-dioxide rich environment.
“If you had a thick atmosphere of carbon dioxide, you should have abundant carbonates,” Chevrier said in 2007. “So far no one has seen even a grain of carbonate.”
It is possible, he noted, that a different greenhouse gas, perhaps methane, could have warmed the atmosphere. On Earth, methane is strongly associated with organic material. And the presence of methane has been a tantalizing possibility ever since Mariner 7 detected a whiff of it on a 1969 flyby. But that turned out to be a false positive. And methane “plumes” detected in 2003 and 2004 that appeared and disappeared were hotly debated. Were they seasonal clouds, or a malfunctioning instrument?
When the Curiosity rover landed in 2012, scientists hoped the mystery would be solved. Curiosity sampled the atmosphere six times in late 2012 and early 2013, and found nothing. Then it tried again in 2013 and found methane. Some researchers are convinced there’s methane on Mars, others are sure they’re seeing another false hit.
Meanwhile, center researchers turned their attention to gullies. On Earth, gullies are associated with water. Mars researchers had widely theorized that Martian gullies were created long ago when conditions on the surface were more favorable to liquid water. Then, in 2005, the Mars Global Surveyor spacecraft noticed deposits that hadn’t been there a few years prior, suggesting recent water activity. With the help of a graduate student, Chevrier created a model that could account for liquid water on Mars. They used a brine containing ferric sulfate, which is found in some Martian formations. It had a freezing point of minus 68 degrees Celsius, low enough to sometimes be liquid on the planet’s surface. Next, they created a map showing where such a brine might be found above and below the surface of Mars, and where it might be frozen and where it might be liquid. As it turned out, areas with gullies strongly correlated to zones where the brine could be in a liquid state.
Continuing research with other Martian compounds indicated brines had potential. Using the center’s planetary simulation labs, researchers demonstrated that perchlorates similar to those found by the Phoenix lander in 2008 could create stable brines in Mars-like conditions. The next step was to look at how the atmosphere interacted with Martian soil to possibly produce water. Phoenix collected six months of temperature, humidity and other atmospheric data, which Chevrier and center graduate students analyzed for clues.
In May 2015, months before NASA’s announcement that there is in fact water on Mars, Chevrier was an author on a Nature Geoscience article that indicated perchlorate brines could exist on Mars and might explain dark streaks called recurring slope lineae. That is what NASA announced in September 2015.
The larger question of life on Mars remains. After 10 years of studying Mars, Chevrier has his doubts. “If we combine observations with the thermodynamics of brine formation and the current knowledge about terrestrial organisms, is it possible to find a way for organisms to survive in Martian brines? My answer is no.”
If we combine observations with the thermodynamics of brine formation and the current knowledge about terrestrial organisms, is it possible to find a way for organisms to survive in Martian brines? My answer is no.
