A new analysis of sediment samples collected by the rover has revealed the presence of carbon – and the possible presence of ancient life on the Red Planet is just one possible explanation for why it is there.
This is why carbon atoms – with their own recycling cycle – are trace elements 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 material, such as a Martian sediment, they can shed light on a planet’s carbon cycle, no matter when it occurred.
Knowing more about the origin of this newly discovered Martian carbon could also reveal the process of the carbon cycle on Mars.
Secrets in the sediment
Curiosity landed in Gale Crater on Mars in August 2012. The 96-mile (154.5 km) crater, named after Australian astronomer Walter F. Gale, is likely the result of a meteorite impact between 3.5 billion and 3.8 billion years ago. The Great Cove likely contained a lake, and now it houses a mountain called Mount Sharp. The crater also includes layers of exposed old rock.
To take a closer look, the probe was drilled to collect sediment samples through the crater between August 2012 and July 2021. Curiosity then heated these 24 powder samples to about 1,562 degrees Fahrenheit (850 degrees Celsius) in order to separate the 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.
Carbon was depleted in some samples while others were enriched. Carbon has two stable isotopes, measured as either carbon 12 or carbon 13.
House, lead study author and professor of Earth sciences at Penn State University, said in a statement: “The samples highly depleted in carbon 13 are somewhat similar to samples from Australia taken from 2.7 billion-year-old sediments.”
“These samples were the result of biological activity when methane was consumed by ancient microbial mats, but we can’t necessarily say that on Mars because it is a planet that may have formed from different materials and processes than Earth.”
In lakes on Earth, microbes like to grow in large colonies that essentially form mats just below the surface of the water.
3 potential sources of carbon
The various measurements of these carbon atoms could indicate three things very different about ancient Mars. The origin of the carbon is likely due to cosmic dust, ultraviolet decomposition of carbon dioxide, or ultraviolet decomposition of biologically produced methane.
According to the researchers, “all three of these scenarios are unconventional, in contrast to common processes on Earth.”
The first scenario involves our entire solar system passing through a cloud of galactic dust, something that happens every 100 million years, according to House. A particle-laden cloud can lead to cooling events on rocky planets.
“It doesn’t deposit a lot of dust,” House said. “It’s hard to see any of these deposition events in the Earth’s record.”
But it’s possible that during an event like this, the cosmic dust cloud lowered temperatures on ancient Mars, which may have contained liquid water. This could cause glaciers to form on the surface of Mars, leaving a layer of dust on top of the ice. When the ice melts, the sediment layer including carbon will remain. While it’s entirely possible, there is little evidence of glaciers at Gale Crater and the study authors said more research is needed.
The second scenario involves converting carbon dioxide on Mars into organic compounds, such as formaldehyde, due to ultraviolet radiation. This hypothesis also requires additional research.
The third method for producing this carbon has potential biological roots.
It is also possible that methane reacted with ultraviolet radiation, leaving a trace of carbon on the surface of Mars.
More pits on the horizon
Curiosity will return to the site where it collected the majority of samples in about a month, allowing another opportunity to analyze sediments from this interesting site.
“This research fulfilled the long-term goal of exploring Mars,” House said. “To measure the various carbon isotopes – one of the most important tools of geology – from sediments in another habitable world, and this is done by looking at nine years of exploration.”
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