New findings from NASA’s Curiosity Rover provide evidence that significant amounts of oxygen once permeated the atmosphere of ancient Mars. The Red Planet, it would seem, was more Earth-like than we thought.
This higher oxygen level can be linked to a time when groundwater was present in the planet’s Gale Crater where the rover is based, and it adds to other Curiosity findings – such as evidence of ancient lakes – revealing how Earth-like our neighbouring planet once was.
“The only ways on Earth that we know how to make these manganese materials involve atmospheric oxygen or microbes,” said Nina Lanza, a planetary scientist at Los Alamos National Laboratory in New Mexico. “Now we’re seeing manganese oxides on Mars, and we’re wondering how these could have formed?”
“These high manganese materials can’t form without lots of liquid water and strongly oxidising conditions. 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 history, the appearance of high concentrations of manganese oxide minerals is an important marker of a major shift in our atmosphere’s composition, from relatively low oxygen to the current oxygen-rich atmosphere.
The presence of the same types of materials on Mars suggests oxygen levels rose there, too, before declining to their present values. But how did that oxygen-rich environment form?
“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,” added Lanza. “It’s thought that at this time in Mars’ history, water was much more abundant.”
Yet without a protective magnetic field as seen on Earth, ionising radiation began splitting water molecules into hydrogen and oxygen. This, coupled with Mars’ relatively low gravity, meant the planet wasn’t able to hold onto the lightest of hydrogen atoms, while leaving the heavier oxygen atoms behind.
Much of this oxygen went into rocks, leading to the rusty red dust that covers the surface today.
“It’s hard to confirm whether this scenario for Martian atmospheric oxygen actually occurred,” continued Lanza. “But it’s important to note this idea represents a departure in our understanding for how planetary atmospheres might become oxygenated.”
Curiosity has been investigating sites in Gale Crater since 2012. The high-manganese materials it found are in mineral-filled cracks in sandstones in the “Kimberley” region of the crater.
Nasa’s Opportunity rover, exploring Mars since 2004, also recently discovered high manganese deposits thousands of miles from Curiosity. This supports the idea the conditions needed to form these materials were present beyond Gale Crater.
Agencies/Canadajournal