Could life have started on Mars billions of years ago? An experiment simulating the origin of life under Martian conditions suggests that it might have done, but only in certain regions where conditions were unusually hospitable.
If life ever existed on Mars, it is conceivable that it began with RNA, which is similar to the DNA that carries our genes. Many scientists suspect that RNA played a key role in life鈥檚 beginnings on Earth, and some even argue that the first life was solely based on RNA: an idea called the 鈥�RNA World鈥�.
To see if that scenario could have played out on Mars, Angel Mojarro at the Massachusetts Institute of Technology and his colleagues simulated the environment on Mars around 4 billion years ago.
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There is no hard evidence for life on Mars today. A key obstacle is the planet鈥檚 frigid climate, which means there is little liquid water. However, there is evidence that there was running water on Mars billions of years ago.
Mojarro鈥檚 team placed RNA-like molecules in water that contained dissolved metals and other chemicals. These solutions mimicked water on Mars billions of years ago, which would have contained metals leached out of rocks, and would have been affected by the atmospheric chemistry.
They tracked how long the molecules lasted before breaking apart. To do this as precisely as possible, they built them mostly out of DNA building blocks, with just one RNA building block inserted 鈥� DNA and RNA contain different sugars, so the team could be sure they were only looking at breakage at the points where RNA-like molecules broke.
The RNA-like molecules were most stable in mildly acidic water containing magnesium ions, which would be expected if the water were resting on basalt: a rock that forms when lava from a volcano cools.
That means a Martian RNA World is plausible, the authors say. However, it does limit the options, because previous studies of Martian geochemistry suggest that much of the planet鈥檚 past water was neutral rather than acidic. Gale Crater, which NASA鈥檚 Curiosity rover is exploring, may once have been such a lake.
鈥淒id the conditions exist on Mars such that an RNA World could operate?鈥� asks Jack Mustard of Brown University in Rhode Island. 鈥淭hey make the case that that鈥檚 true.鈥�
However, Mustard says the results should be treated with caution, because there are 鈥渧ery large uncertainties鈥� about what conditions on Mars were really like when the planet was young.
A key test will be to bring samples of Martian soil back to Earth, to see if they have been modified by life, says Mustard. NASA鈥檚 Perseverance rover, which launches in July, will collect samples and pack them into test tubes for a later rover to collect.
Reference: BioRxiv, DOI:
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