In an afternoon announcement led by a team of NASA scientists delivered jointly from the Goddard Space Center in Maryland and the Jet Propulsion Laboratory (JPL) in Southern California, the American space agency revealed that its Curiosity rover on Mars had discovered organic molecules on Mars in rock samples from an ancient lakebed.
“We detected a variety of molecules,” including “benzene and other molecules with [carbon] chains,” geologist and biochemist Jennifer Eigenbrode explained during the presentation.
“We’re looking at ancient rocks that are three billion years old,” she said. Eigenbrode clarified that Curiosity found these samples by “drill[ing] in the top five centimeters.” “That rock has been sitting at the surface for an extended period of time,” she explained.
This was notable because the surface of Mars, due to its thin atmosphere, is bombarded with cosmic rays from the sun and distant astrophysical events that affect the composition of the first meter and a half of the Martian surface.
Still, organic molecules do not necessarily mean that life ever existed on Mars, as the NASA scientists were quick to explain.
“The organic molecules we found are not specific evidence of life,” Dr. Eigenbrode explained. “It’s not like the ‘organic’ produce” you buy at the grocery store, she added.
The Curiosity rover, which touched down on Mars in August 2012, is equipped with a drilling mechanism that vaporizes surface samples, then uses a mass spectrometer to identify what molecules the drilling samples consist of. Spectrometry works by vaporizing molecules and atoms and observing their light emission patterns; all molecules and atoms have unique patterns of light emission, which allow scientists to identify their composition.
The presence of organic compounds in one Martian lakebed might hint that other spots on Mars are rich with similar organic compounds.
In addition to the discovery of organic compounds in Martian lakebeds, scientists also discovered a seasonal pattern of atmospheric methane on Mars, which repeated in a regular cycle. Methane, too, is an organic molecule produced by many lifeforms on Earth, but which also exists in the universe independent of life.
“We’re announcing the discovery of a repeatable pattern in methane measurements,” Dr. Chris Webster explained. Webster said that the seasonal cycle of methane in the Martian atmosphere varied “by a factor of three.”
While scientists do not yet know what is causing the periodic methane spikes, Webster said that they had ruled out some possibilities, and had some theories. “The idea that best fits our data is the idea of subsurface storage,” Webster said — meaning the methane “may be trapped” deep underground, Webster added. “We don’t know if it’s ancient or modern,” he clarified. He speculated that the methane could be produced by natural processes or perhaps by methanogenic organisms, similar to those on Earth.
Astrobiologists have been fascinated by Martian geology for decades. As a rocky planet with a comparable geologic history to Earth, understanding the history of Martian geology may give hints into how common or uncommon life is in the universe. While observational evidence suggests that it is unlikely that complex organisms ever existed on Mars, it is possible that single-cell organisms may have existed at one point in its history. Life on Earth first appeared around 4.2 billion years ago; yet, it took around 2.5 billion years before multi-cellular life appeared. If the history of life on other planets is similar, single-celled organisms may be the first thing to search for.