Today, Mars is a radioactive icebox covered in rust, but billions of years ago, it was warm, wet and blue-skied. Could life, in some form, have once called the Red Planet home?
In a milestone study published in Nature Communications, an international team of scientists, including Ross Williams from Notre Dame’s Department of Civil and Environmental Engineering and Earth Sciences, confirmed the presence of 21 different organic molecules in a single sample with 7 of them detected on Mars for the very first time.
Meteorites, comets, and volcanic reactions litter the Martian surface with simple carbon molecules, but the complex macromolecular matter targeted by NASA’s Curiosity rover represents a significantly higher tier of chemical organization—one that is much harder for a volcano or a meteorite to create accidentally.
“On Earth, you can go back billions of years and still find organic matter,” said Williams, whose work as a postdoctoral researcher at NASA contributed to the paper’s findings. “But Earth has an atmosphere, magnetosphere, and far less radiation reaching the surface than Mars. So, the question we had to answer was: if life existed on Mars billions of years ago, would we still even be able to find it?”
Credit: The Lunar and Planetary Institute; NASA’s MAVEN mission
In 2012, Curiosity landed in the 96-mile-wide Gale Crater and has been relaying data and photos ever since. The crater was an ideal place to search for organic material since the topography revealed clear traces of the planet’s once vast river deltas and lake beds. Organic material hitching a ride in the moving water would have settled out and become trapped in the layers of mud that eventually solidified into sandstone.
Despite the promising terrain, the team had to wait eight years before identifying an ideal sample site. They had only two chances to carry out their experiment, which required saturating the sample with a single-use chemical, tetramethylammonium hydroxide (TMAH), and then baking it at a toasty 1022 degrees Fahrenheit in the rover’s plutonium-powered oven. TMAH was needed to coax the organic material out of the tight grip of Martian clay.
Among the 21 distinct organic molecules identified from the rover’s data, two, naphthalene and benzothiophene, are chemically rigid, stable building blocks of complex macromolecules thus proving—Mars had a rich organic inventory.
Curiosity used a gas chromatograph-mass spectrometer—a highly sophisticated instrument for breaking apart and sorting materials to identify their chemical fingerprints—to carry out the team’s experiment. Williams, an expert in mass spectrometry and geochemistry, is currently involved with efforts to sleuth out evidence of past climate changes on Earth at Notre Dame’s Molecular Paleoclimatology and Organic Biogeochemistry (MAB) lab.
“My biggest takeaway from this research is that despite the radiation and extreme, harsh environment on Mars’ surface, this indigenous organic matter was preserved in Martian rock. This is encouraging for future studies addressing the topic of life,” said Williams. “What most people in our community agree upon is that we could get closer to unraveling these mysteries if we could just get the rocks back to our labs on Earth.”
The retrieval of Martian rocks can be explored through NASA Mars Sample Return Mission Overview, which highlights the overarching goals and technological hurdles scientists face in bringing these rocks to Earth.
—Karla Cruise, Notre Dame Engineering. Photo courtesy of NASA/JPL-Caltech/MSSS.