As far as we know, we’re the only habitable planet in the Solar System. We have yet to discover life elsewhere, but Mars – even today – is a pretty good bet. It’s got salty, liquid water on its surface, and although its atmosphere is thin and insubstantial, microbial life could lurk within the sediments, where it’s shielded from incoming solar radiation.
However, as researchers are continuously discovering, Mars was likely once far more habitable. Recent data from NASA’s Mars Atmosphere and Volatile Evolution (MAVEN) mission revealed that its once-thick atmosphere, held in place by a wavering magnetosphere, was stripped away by major solar storms. Now, another NASA mission called SOFIA – the Stratospheric Observatory for Infrared Astronomy – has found that there are traces of atomic oxygen still lingering in the gaseous envelope that surrounds the Red Planet.
Atomic oxygen was first detected in the Martian atmosphere 40 years ago by the Viking and Mariner missions, but it hasn’t been picked up since. “Atomic oxygen in the Martian atmosphere is notoriously difficult to measure,” said Pamela Marcum, SOFIA project scientist, in a statement.
SOFIA, a flying observatory attached to a Boeing 747SP, looks at the infrared part of the electromagnetic spectrum. It’s designed to peer into the hearts of stars, the complex clouds of planetary nebulae, and the atmospheres of planets – both outside the Solar System and those right next door to us.
“To observe the far-infrared wavelengths needed to detect atomic oxygen, researchers must be above the majority of Earth's atmosphere and use highly sensitive instruments, in this case a spectrometer,” Marcum added. “SOFIA provides both capabilities.”
Flying between 11.3 and 13.7 kilometers (37,000 and 45,000 feet) above ground, specialized detectors were able to spy atomic oxygen in the mesosphere (the upper atmosphere) of Mars, confirming it as not just an erroneous detection of Earth’s far more abundant atmospheric oxygen. The data from SOFIA was published in the journal Astronomy and Astrophysics.
Although this atomic oxygen is a far cry from the amount of molecular, breathable oxygen (O2) seen on a planet covered in photosynthesizing bacteria and plants like ours, its discovery is nonetheless important: It is the key element controlling several atmospheric processes, including energy and mass flow into and out of the planet; in addition, it controls how much heat is lost from Mars’ carbon dioxide.
Ultimately, its presence influences how fast the atmosphere is disappearing into space. Understanding the atomic oxygen segment of the Martian atmosphere will allow researchers to gain a better understanding of why it was all but obliterated over the last few billions of years.
The researchers actually found half as much oxygen as they expected to find, but they put this down to natural variations in the Martian atmosphere. It’s not yet clear where this atomic oxygen originated from, but seeing as it’s the third most abundant element in the universe, its discovery wasn’t entirely surprising.
It is worth pointing out that the ancient atmosphere of Mars probably did contain far more oxygen than it currently does. Whether it was produced by chemical reactions in the atmosphere, or primitive life at the surface, is currently unknown.
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