Organic carbon found on Mars may come from life that once thrived on the Red Planet, according to research from Penn State University.
The building blocks of life were in rocks collected by NASA’s rover Curiosity. They could have a “biological basis,” say scientists. The samples resemble fossilized remains of microbial life in Australia that date back 2.7 billion years.
Analysis of sediments from half a dozen locations, including an exposed cliff, identified an ancient carbon cycle. The chemical element has two stable isotopes — 12 and 13. Looking at the amounts opens a window into its origin.
“The samples extremely depleted in carbon 13 are a little like samples from Australia taken from sediment that was 2.7 billion years old,” says lead author Christopher House, a professor of geosciences, in a statement. “Those samples were caused by biological activity when methane was consumed by ancient microbial mats. But we can’t necessarily say that on Mars because it’s a planet that may have formed out of different materials and processes than Earth.”
On Earth it would indicate past microbes consumed microbially produced methane.
Ancient Mars may have had large plumes of methane being released from the subsurface where production would have been energetically favorable. Then, the released methane would either be consumed by microbes or react with ultraviolet light and be deposited directly on the surface.
Methane – the simplest organic molecule – is known to be present in Mars’ atmosphere.
Curiosity has been roaming Gale Crater for over nine years, drilling under the surface and sending the results back home. It’s believed to have been a deep lake 3.5 billion years ago containing complex organic molecules, the key raw materials for life as we know it.
“The amounts of carbon 12 and carbon 13 in our solar system are the amounts that existed at the formation of the solar system,” says House. “Both exist in everything, but because carbon 12 reacts more quickly than carbon 13, looking at the relative amounts of each in samples can reveal the carbon cycle.”
Curiosity heated the samples in the absence of oxygen to separate any chemicals. Scans showed some were exceptionally depleted in carbon 13 while others were enriched.
Other plausible theories include a cosmic dust cloud, or ultraviolet radiation breaking down carbon dioxide.
“All three of these scenarios are unconventional, unlike processes common on Earth,” notes House, who believe the finding the remains of microbial mats could clear things up.
NASA’s rover Perseverance which landed in February 2021, has focused on the Jezero crater – the site of an ancient lake – for signs of past life.
“We are being cautious with our interpretation – which is the best course when studying another world,” adds House. “This research accomplished a long-standing goal for Mars exploration. To measure different carbon isotopes – one of the most important geology tools – from sediment on another habitable world. It does so by looking at nine years of exploration.”
The study is published in Proceedings of the National Academy of Sciences.
South West News Service writer Mark Waghorn contributed to this report.