Mars may have been less oxygen-rich than previously assumed

But there's still a possibility of life on the Red Planet, finds study
Ancient Mars is estimated to have had 99.9 per cent of carbon dioxide (CO2) in the atmosphere, higher than the current 96 per cent. Photo: iStock
Ancient Mars is estimated to have had 99.9 per cent of carbon dioxide (CO2) in the atmosphere, higher than the current 96 per cent. Photo: iStock

Ancient Mars was probably warmer and wetter, but it seems to have lacked an oxygen-rich atmosphere — an essential ingredient of life on Earth, according to a new study.

These findings, however, do not rule out the possibility that life previously existed on the Red Planet, the study published in journal Nature Geoscience noted. 

For example, extremophiles — organisms that can live in extreme environments— are known to thrive without oxygen on Earth. Further, the new study contradicts previous research suggesting Mars had an oxygen-rich environment billions of years ago.

In 2016, scientists detected manganese oxide minerals on the Red Planet. This led scientists to believe that our neighbouring planet had more oxygen in the past than it does today. The researchers noted that Earth’s atmosphere has about 20,000 times as much oxygen as Mars’.

The 2016 research reported that manganese, water and strongly oxidising conditions combined to produce manganese oxide minerals on our neighbouring planet.

But Jeffrey Catalano, professor of Earth and planetary sciences in Arts and Sciences and the new study’s author, was convinced that the theory lacked teeth. 

“When studies claimed that manganese oxides on Mars were signs of oxygen in the ancient atmosphere, this immediately felt like a questionable conclusion,” Catalano told Down To Earth.

The time needed to produce observable manganese oxides in the presence of oxygen is implausibly long, he explained.

Halogen elements chlorine and bromine, which are present at high levels on Mars, likely played a role in the formation of manganese oxide minerals, Catalano and his colleagues speculated.

The researchers conducted a series of experiments in their laboratory. They tested how chlorate and bromate — dominant forms of these elements on Mars — oxidise manganese in water samples.

Their results showed that chlorate and bromate converted manganese dissolved in water into manganese oxide minerals. But it does the job thousands to millions of times faster than oxygen.

Further, ancient Mars is estimated to have had 99.9 per cent of carbon dioxide (CO2) in the atmosphere, higher than the current 96 per cent. High CO2 levels make the water acidic. 

The expert explained that manganese oxidation by oxygen is either exceptionally slow or chemically impossible with acidic conditions.

The researchers believe that the rock samples collected from Mars could settle the debate on whether the Red Planet had an oxygen-rich environment in the past.

Martian rock samples are expected to arrive on Earth in 2033. “Getting samples back to Earth in the 2030s will allow us to better probe the signature of past oxygen availability on Mars,” Catalano said.

Billions of years ago, Earth also had a low-oxygen environment. That changed roughly 2.5 billion years ago, thanks to photosynthesis provided by the first forms of life.

The researchers said that the hunt for past life should continue.

“I don’t think of it [the new findings] as a ‘setback’ to habitability — only that there were probably no oxygen-based lifeforms,” Kaushik Mitra, now a postdoctoral research associate at Stony Brook University and the study’s author, said in a statement.

Mars was likely suitable for salt-loving organisms, he added.

In the future, the team hopes to study Europa and Enceladus, moons orbiting Jupiter and Saturn. Scientists speculate that these ocean worlds are likely habitable.

They aim to study oxidation processes in these ocean worlds. Oxidations, which allow the loss of electrons from molecules, produce energy. “All life gains energy through oxidation processes,” Catalano explained.

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