Mars used to have an Earth-like atmosphere

An analysis of Martian rocks by NASA’s Curiosity rover has indicated the Red Planet used to have a higher level of oxygen in its atmosphere than it currently does, according to a new report in Geophysical Research Letters.

Scientists discovered high amounts of manganese oxides using a laser device on the rover. This telltale sign of higher oxygen amounts in Mars’ early atmosphere adds to other Curiosity findings that revealed how Earth-like the nearby planet used to be.

This study also adds critical context to other clues regarding atmospheric oxygen levels in Mars’ past. The manganese oxides were discovered in mineral veins located within a region the Curiosity mission has focused on to understand the timeline of ancient Martian ecological conditions. Within that context, the greater oxygen level can be associated with a time when groundwater sat in Mars’ Gale Crater, where the rover has been exploring.

“The only ways on Earth that we know how to make these manganese materials involve atmospheric oxygen or microbes,” Nina Lanza, a planetary scientist with NASA, said in a news release. “Now we’re seeing manganese oxides on Mars, and we’re wondering how the heck these could have formed?”

Finding could lead to discovery of microbial life on Mars

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“These high manganese materials can’t form without lots of liquid water and strongly oxidizing conditions,” Lanza said. “Here on Earth, we had lots of water but no widespread deposits of manganese oxides until after the oxygen levels in our atmosphere rose.”

In Earth’s geological record, high levels of manganese oxide minerals are a critical marker of the significant change in our atmosphere’s composition, from fairly low oxygen to the oxygen-rich atmosphere we see today. The existence of the same kinds of materials on Mars indicates that oxygen amounts rose there, too, before falling to their present levels.

“One potential way that oxygen could have gotten into the Martian atmosphere is from the breakdown of water when Mars was losing its magnetic field,” Lanza said. “It’s thought that at this time in Mars’ history, water was much more abundant.”

Without a magnetic field to guard the planet’s surface, ionizing radiation would split water molecules into hydrogen and oxygen. Because of Mars’ relatively low gravity, the planet wasn’t able to retain hydrogen atoms. However, heavier oxygen atoms remained behind, got trapped in rocks and caused the rusty red dust we see on Mars today. While the red iron oxides need just mildly-oxidizing situation to develop, manganese oxides need a strong-oxidizing environment.

“It’s hard to confirm whether this scenario for Martian atmospheric oxygen actually occurred,” Lanza said. “But it’s important to note that this idea represents a departure in our understanding for how planetary atmospheres might become oxygenated.”

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Image credit: NASA

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