Ancient life may be just one possible explanation for Mars rover’s latest discovery

A new analysis of sediment samples collected by the rover revealed the presence of carbon — and the possible existence of ancient life on the red planet is just one potential explanation for why it may be there.

Carbon is the foundation for all of life on Earth, and the carbon cycle is the natural process of recycling carbon atoms. On our home planet, carbon atoms go through a cycle as they travel from the atmosphere to the ground and back to the atmosphere. Most of our carbon is in rocks and sediment and the rest is in the global ocean, atmosphere and organisms, according to NOAA, or the National Oceanic and Atmospheric Administration.

That’s why carbon atoms — with their cycle of recycling — are tracers of biological activity on Earth. So they could be used to help researchers determine if life existed on ancient Mars.

When these atoms are measured inside another substance, like Martian sediment, they can shed light on a planet’s carbon cycle, no matter when it occurred.

Learning more about the origin of this newly detected Martian carbon could also reveal the process of carbon cycling on Mars.

A study detailing these findings published Monday in the journal Proceedings of the National Academy of Sciences.

Secrets in the sediment

Curiosity landed in Gale Crater on Mars in August 2012. The 96-mile (154.5-kilometer) crater, named for Australian astronomer Walter F. Gale, was probably formed by a meteor impact between 3.5 billion and 3.8 billion years ago. The large cavity likely once held a lake, and now it includes a mountain called Mount Sharp. The crater also includes layers of exposed ancient rock.

The image shows a drill hole made by Curiosity on Mars' Vera Rubin Ridge.

For a closer look, the rover drilled to collect samples of sediment across the crater between August 2012 and July 2021. Curiosity then heated these 24 powder samples to around 1,562 degrees Fahrenheit (850 degrees Celsius) in order to separate elements. This caused the samples to release methane, which was then analyzed by another instrument in the rover’s arsenal to show the presence of stable carbon isotopes, or carbon atoms.

Curiosity rover searches for salt on Mars

Some of the samples were depleted in carbon while others were enriched. Carbon has two stable isotopes, measured as either carbon 12 or carbon 13.

“The samples extremely depleted in carbon 13 are a little like samples from Australia taken from sediment that was 2.7 billion years old,” said Christopher H. House, lead study author and professor of geosciences at Pennsylvania State University, 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.”

In lakes on Earth, microbes like to grow in big colonies that essentially form mats just under the surface of the water.

3 possible carbon origins

The varied measurements of these carbon atoms could suggest three very different things about ancient Mars. The origin of the carbon is likely due to cosmic dust, ultraviolet degradation of carbon dioxide, or the ultraviolet degradation of biologically produced methane.

“All three of these scenarios are unconventional, unlike processes…