The findings come from a chemical experiment performed for the first time on another world, revealing that the Martian surface can preserve the kinds of molecules that could serve as signs of ancient life. However, the experiment cannot distinguish between organic compounds from potential past life on Mars and those formed through geologic processes or delivered by meteorites. Definitively identifying signs of past life would require returning rock samples to Earth.
The study was led by Amy Williams, Ph.D., a professor of geological sciences at the University of Florida and a scientist on the Curiosity and Perseverance Mars rover missions.
"We think we're looking at organic matter that's been preserved on Mars for 3.5 billion years," said Williams. "It's really useful to have evidence that ancient organic matter is preserved, because that is a way to assess the habitability of an environment. And if we want to search for evidence of life in the form of preserved organic carbon, this demonstrates it's possible."
Among the 20-plus chemicals identified by the experiment, Curiosity spotted a nitrogen-bearing molecule with a structure similar to DNA precursors - a chemical never before found on Mars. The rover also identified benzothiophene, a large, double-ringed, sulfurous chemical often delivered to planets by meteorites.
"The same stuff that rained down on Mars from meteorites is what rained down on Earth, and it probably provided the building blocks for life as we know it on our planet," Williams said.
The experiment was conducted in 2020 in the Glen Torridon region of Gale crater, an area rich in clay minerals that indicate the area once contained water. Those clays can hold on to and preserve organic chemicals better than other minerals, making them a prime target for uncovering these compounds.
The experiment was conducted by the instrument suite known as the Sample Analysis at Mars, or SAM. Led in part by Jennifer Eigenbrode, Ph.D., an astrobiologist at NASA's Goddard Space Flight Center, SAM has been responsible for many of the mission's most important discoveries about organic chemistry, atmosphere, and habitability on Mars.
Using a chemical known as TMAH, the experiment broke apart larger organic molecules so they could be analyzed by onboard instruments within SAM. With only two cups of the TMAH chemical onboard Curiosity, success required careful planning and choosing the most favorable location to sample.
The promising results come as future missions - including the Rosalind Franklin mission to Mars and the Dragonfly expedition to Saturn's moon Titan - plan to bring the TMAH test onboard to search for organic compounds.
"We now know that there are big complex organics preserved in the shallow subsurface of Mars, and that holds a lot of promise for preserving large complex organics that might be diagnostic of life," Williams said.
Research Report:Diverse organic molecules on Mars revealed by the first SAM TMAH experiment
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