NASA's Curiosity Mars rover hasn't found signs of alien life, but one of its wheeled brethren just might do so a few short years from now.
Yesterday (June 7), Curiosity mission scientists hit the world with an astrobiological one-two punch. The rover, they announced, had spotted organic molecules in ancient Red Planet rocks and identified a seasonal cycle in the concentration of atmospheric methane, suggesting that the gas is leaking from underground reservoirs.
This is exciting stuff. Organics are the carbon-containing building blocks of life as we know it, and about 95 percent of the methane in Earth's air is emitted by microbes and other organisms. Still, neither find constitutes evidence of life, as Curiosity team members were careful to stress yesterday; organics and methane can be produced by geological processes, and the origin of the stuff Curiosity observed remains unknown. [The Search for Life on Mars: A Photo Timeline]
In fact, Curiosity isn't equipped to hunt for life; its main goal is to determine if Mars has ever been capable of supporting microbes. The rover mission has achieved that goal, showing that its landing site, the floor of a huge crater called Gale, harbored a potentially habitable lake-and-stream system long ago.
But life-hunting Mars missions are coming, and soon. In 2020, NASA plans to launch a rover that will seek out organics and search for chemical signatures of life in ancient Red Planet rocks. The Mars 2020 rover, whose body is based heavily on that of Curiosity, will also collect and cache samples for eventual return to Earth, where scientists could scrutinize them for any evidence of native Martians. (This latter bit is speculative, however, because no sample-retrieval mission is officially on NASA's books at the moment.)
The European-led ExoMars rover is also scheduled to lift off in 2020. This vehicle is a life hunter as well, and it will take the search deep underground, using a drill that can dig about 6.5 feet (2 meters) down. (Like Curiosity, Mars 2020 will use a drill that can bore about 2.5 inches, or 6 centimeters, into rock.)
"By doing so, it might get away from the [Martian] radiation environment, which can be very damaging to organic molecules," said Jennifer Eigenbrode, a scientist at the Solar System Exploration Division at NASA's Goddard Space Flight Center in Greenbelt, Maryland. (Mars gets hammered by solar and cosmic radiation, because it lacks a global magnetic field and has a thin atmosphere.)
"ExoMars might even come across stuff that's significantly better preserved, [allowing it to] tease out some information on source," Eigenbrode, who led the newly published Curiosity organics-detection study, told Space.com.
ExoMars could also shed considerable light on the origins of Red Planet methane, said Chris Webster, who led the new Curiosity methane study. The ExoMars rover will likely be able to characterize the carbon in methane molecules, determining how much of it is carbon-13, which contains one more neutron in its nucleus than a "normal" carbon-12 atom. (A methane molecule consists of a single carbon atom bonded to four hydrogen atoms.)
"Even in relatively low methane abundances, they should be able to get the carbon-13 ratio," Webster, a senior research fellow at NASA's Jet Propulsion Laboratory in Pasadena, California, told Space.com, referring to the ExoMars team.
That ratio will be very interesting to astrobiologists, because biologically produced methane here on Earth is significantly depleted in carbon-13.
The ExoMars rover mission is the second phase of the two-part ExoMars program, which the European Space Agency (ESA) heads, with Russia as a primary partner. NASA is involved as well; for example, the American space agency is providing key components for the rover's main astrobiology instrument, the Mars Organic Molecule Analyzer. [Photos: Europe's ExoMars Missions to Mars in Pictures]
The first phase of ExoMars launched the Trace Gas Orbiter (TGO) and a landing demonstrator called Schiaparelli toward the Red Planet in March 2016. Schiaparelli ended up crashing into the Martian surface, but TGO arrived safely and recently settled into its final orbit. The probe's measurements should allow researchers to make global maps of methane and other low-abundance gases in Mars' air, ESA officials have said.
These maps could help guide future life-hunting surface craft to promising locales, Webster said.
"The big question is, will they see plumes or patches or spikes?" Webster said. "If they could tell us there's a region of Mars where the methane seems to be coming from, that would be huge. Now we can direct future missions in that direction."
Nobody knows, of course, whether microbes or any other organisms have ever called Mars home. But Curiosity's discoveries are cause for some optimism in this regard, NASA officials said.
"With these new findings, Mars is telling us to stay the course and keep searching for evidence of life," Thomas Zurbuchen, associate administrator for the Science Mission Directorate at NASA headquarters in Washington, D.C., said in a statement. "I'm confident that our ongoing and planned missions will unlock even more breathtaking discoveries on the Red Planet."