We’ve learned a great deal about Mars over the last two decades, thanks to the long-term success of multiple orbital missions and rovers. It’s now considered likely that liquid water once flowed across the planet, and there’s evidence that Mars was once much warmer than it is today thanks to the greenhouse effect. One enduring question, however, has been the composition of the ancient Martian atmosphere. New research from Curiosity suggests that Mars’ atmosphere once contained considerable amounts of oxygen, hinting at a more Earth-like past.
Today, Mars’ atmosphere is a thin layer composed almost entirely (96%) of carbon dioxide. The average atmospheric pressure is roughly 0.6% of Earth’s sea level equivalent. Even at the bottom of the Hellas Planitia, the largest impact crater in the solar system, the pressure is estimated at just 1.1% of Earth standard. Curiosity’s latest analysis found evidence of manganese oxides on the surface of the planet, however, implying that the primordial environment of the Red Planet was a very different place.
“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 the heck these could have formed?
There are two known methods by which such materials could have formed: High levels of oxygen in the atmosphere, or via microbes. The area where Curiosity found the minerals has already been confirmed to be linked to time when groundwater was present in the area, but water alone isn’t enough to create the mineral deposits — the amount of oxygen in the atmosphere would also have been high as well.
Since there’s still no proof that life once existed on Mars, the inorganic explanation for the planet’s manganese oxides is more likely. As Mars’ core cooled, the dynamo that created its planetary magnetic field faded, leaving only partial fields that cover specific regions of the planet, but no comprehensive shield. This allowed ionizing radiation to split water molecules into their constituent parts, hydrogen and oxygen. The hydrogen would’ve been lost to space, while the oxygen was bound into the rocks themselves, giving Mars its distinctive color and nickname.
The potential flaw in this theory is that manganese oxides require much more oxygen to form than iron oxides, which again, points to more free oxygen in the Martian atmosphere than had previously been expected. Even if Mars’ atmosphere contained much more oxygen than originally thought, it’s not clear if the element was produced through biological processes (think simple microbial life) or through another method.
The NASA report notes that both Opportunity and Curiosity have recently found manganese oxides on Mars, despite being separated by several thousand miles. This suggests that the conditions that created the minerals were global rather than being unique to one particular area. Research published last year suggests that Mars’ atmosphere could have been blasted away by enormous solar flares — while rare on human timescales, such events are common across billions of years.