The atmosphere of Mars may not contain much oxygen, but that doesn’t necessarily mean the planet itself lacks the stuff.  A new calculation of how much oxygen could be dissolved in Martian brines shows that the dusty world may be hiding an abundance of oxygen under its surface – potentially enough to support life.
We know Mars has oxygen on its surface, which is why it looks red: iron in Martian dust reacts with oxygen to create red oxides.
Vlada Stamenković  at NASA’s Jet Propulsion Laboratory in California and his colleagues calculated how much oxygen could be dissolved in salty brines just under the Martian surface. They found that, in certain types of brines under particularly cold conditions, there could be just as much oxygen as there is in Earth’s oceans – enough for microbes and even simple animals like sponges to survive.
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But we’re not entirely sure that there are liquid brines on Mars. There have been hints, like recurring slope lineae – dark lines flowing down hills that appear to be liquid – but none of them have been definitively proven to be made of water or brine.
“There have been various different claims for where we may or may not have seen evidence for these brines existing,” says Kirsten Siebach at Rice University in Texas. “Small amounts of brines would be possible, but we aren’t sure that they’re really there.”
Even if there is oxygen-rich brine on Mars, that’s not a guarantee of life, says Robin Wordsworth at Harvard University. “It’s two sides of the coin in a way,” he says. “If you want respiration oxygen is good, but too much oxidation can be bad for life.” Compounds like hydrogen peroxide can damage cells, which may be particularly bad for primitive lifeforms which don’t have that many cells to begin with.
Nature Geoscience
Article amended on 29 October 2018
We corrected what Martian iron and oxygen do
