UK researchers shine fresh light on the evolution of Mars’ atmosphere

Chemical analysis of Mars has revealed that the carbon monoxide (CO) in the Red Planet’s atmosphere is, compared to Earth, depleted with respect to the isotope carbon-13 (¹³C). This is the opposite of the isotopic makeup of carbon dioxide (CO₂) — the primary component of the Martian atmosphere — which is enriched in ¹³C thanks to the preferential escape of the lighter carbon-12 (¹²C) into space over the course of billions of years. The findings will help scientists better understand how Mars’ atmosphere and climate has changed over time.

The study was undertaken by planetary astronomer Dr Juan Alday of the Open University and his colleagues and was based on data collected by NASA’s ExoMars Trace Gas Orbiter mission.

Dr Alday said: “The key for understanding why there is less ¹³C in CO lies in the chemical relationship between CO₂ and CO.

“When CO₂ molecules are destroyed by sunlight to form CO, ¹²CO₂ molecules are more efficiently destroyed than ¹³CO₂.”

This, he explains, leads “to a depletion of ¹³C in CO over long periods of time”.

While carbon monoxide makes up only a small amount of the Martian atmosphere (an estimated 0.06 percent at the surface, compared to 95 percent for carbon dioxide), the team said that the findings have important implications for our understanding of Mars’ history.

The analysis, they added, shines a light on both how the Martian atmosphere has changed over time, and can also help us determine the climatic conditions that once allowed liquid water to exist on the surface of Mars — as is evidenced by its surface geology.

Dr Alday explained: “We do not know what the atmosphere of early Mars was like, nor what conditions allowed liquid water to flow on the surface.

“The isotopes of carbon in Mars’ atmosphere can help us estimate how much CO₂ there was in the past.

“The new measurements by the ExoMars Trace Gas Orbiter suggest that less CO₂ has escaped the planet than previously thought — and provide new constraints on the composition of this early atmosphere of Mars.”

Recent measurements of material on the surface of Mars by NASA’s Curiosity Rover have revealed a similar depletion of ¹³C as seen in the Red Planet’s carbon monoxide.

Open University ExoMars research group leader and planetary scientist Dr Manish Patel said: “There is a long-standing debate on whether organic material on the surface of Mars was produced by biological or non-biological processes.

“The fact that both atmospheric CO and surface organics share this ¹³C-depleted isotopic signature that Juan has measured may indicate that these organics are more likely to be non-biological in origin.”

However, he added, “other origins cannot be ruled out solely based on this information”.

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UK Space Agency Head of Space Exploration Libby Jackson said: “The UK has played a key role in the development of the Trace Gas Orbiter.

“Since its launch in 2016, the UK Space Agency has provided more than £1.4million towards operations and more than £5million towards data analysis.

“The publication of this paper showcases the best of UK space science. Dr Juan Alday is a promising UK Space Agency-funded Postdoctoral researcher at the Open University, and a great example of the talent we are continuing to support across our institutions.”

The full findings of the study were published in the journal Nature Astronomy.

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