Skip to main content

Curiosity rover discovers a puzzling oxygen mystery on Mars

NASA’s Curiosity rover continues to make discoveries that challenge our understanding of the Martian environment. The latest strange puzzle taxing scientists is the variation of oxygen levels on the planet’s surface, as detected Curiosity’s portable chemistry lab, Sample Analysis at Mars (SAM).

In its journey around the Gale Crater, Curiosity discovered the Martian atmosphere has a composition at the surface of 95% by volume of carbon dioxide (CO2), 2.6% molecular nitrogen (N2), 1.9% argon (Ar), 0.16% molecular oxygen (O2), and 0.06% carbon monoxide (CO). The nitrogen and argon levels follow a predictable seasonal pattern, changing relative to the amount of carbon dioxide. The levels of oxygen, however, didn’t conform to expected patterns, rising by as much as 30% over spring and summer.

Melissa Trainer/Dan Gallagher/NASA Goddard

The varying oxygen levels have scientists perplexed. “The first time we saw that, it was just mind-boggling,” Sushil Atreya, professor of climate and space sciences at the University of Michigan, said in a statement.

The scientists tried various hypotheses to explain the oxygen variation. They checked whether the SAM instrument was functioning correctly and looked at whether carbon dioxide molecules could be breaking apart in the atmosphere to create oxygen, but neither approach yielded results.

“We’re struggling to explain this,” Melissa Trainer, a planetary scientist at NASA’s Goddard Space Flight Center and leader of the research, said in the statement. “The fact that the oxygen behavior isn’t perfectly repeatable every season makes us think that it’s not an issue that has to do with atmospheric dynamics. It has to be some chemical source and sink that we can’t yet account for.”


One possibility is that the oxygen levels are related to another Martian puzzle: The fluctuating levels of methane on the planet. As well as expected seasonal variations in methane levels, Curiosity has detected spikes of methane of up to 60% at some times. Scientists still can’t explain this finding either, but they may have found a link between methane and oxygen levels: It seems like the two gases fluctuate together at certain times.

“We’re beginning to see this tantalizing correlation between methane and oxygen for a good part of the Mars year,” Atreya said. “I think there’s something to it. I just don’t have the answers yet. Nobody does.”

Although both oxygen and methane can be produced biologically, their presence doesn’t necessarily indicate life on the planet. They can also be produced chemically, by water and rocks. Curiosity can only detect the levels of the gases, not their origin, so the source of this mystery remains unknown for now.

The research is published in the Journal of Geophysical Research: Planets.

Editors' Recommendations

Georgina Torbet
Georgina is the Digital Trends space writer, covering human space exploration, planetary science, and cosmology. She…
The Curiosity rover reaches a milestone on Mars
Curiosity Rover

NASA's Curiosity rover, which is currently exploring Mars' Gale Crater, recently marked an impressive milestone: 4,000 days on Mars. The rover landed more than a decade ago on August 5, 2012, and since then it has continued to explore the area, collect rock samples, and make its way up the epic slopes of Mount Sharp.

The 4,000 days are measured in mission time, which is calculated in martian days or sols. Due to the differing rates of rotation of Earth and Mars, a day on Mars is slightly longer than a day on Earth, by about 40 minutes. And also, due to the difference distances between Earth and Mars and the sun, a martian year is longer too - at 668 sols, equivalent to 687 Earth days. Those working on Mars rover missions, especially the rover drivers, have to operate on Mars time, so their schedules are out of sync with typical Earth working hours and they generally work on 90-sol shifts to allow them time to readjust to Earth schedules.

Read more
Map of Mars shows the location of ice beneath the planet’s surface
In this artist’s concept, NASA astronauts drill into the Martian subsurface. The agency has created new maps that show where ice is most likely to be easily accessible to future astronauts.

One of the challenges of sending human explorers to Mars is that, due to the logistics of the journey, they will have to be on the planet's surface for considerably longer than the missions of a few days which have been sent to the moon in the past. That means future explorers will need access to resources like food, water, and oxygen -- and rather than having to carry months' worth of supplies through space, it's far more efficient to find ways to produce those resources on Mars itself.

That's the idea behind searching for water ice deposits on Mars. There's plenty of ice on the surface around the planet's poles, but most mission concepts are more focused on the planet's equatorial region. The good news is that there is ice present in these areas too, but the bad news is that it's primarily located below the surface and is thus hard to locate.

Read more
Perseverance rover catches footage of a dust devil on Mars
mars 2020 perseverance rover

Many of the weather events we experience here on Earth can be found on other planets too, and that includes whirlwinds. Several missions have observed small whirlwinds called dust devils on Mars, and the Perseverance rover recently captured footage of one such dust devil in action as it rolled across the martian surface.

The footage was captured by one of Perseverance's black-and-white navigation cameras, called Navcams, and shows a dust devil moving at a speed of around 12 mph across a regions known as the Thorofare Ridge. You can clearly see the dust devil as a white column moving across the top of the ridge in an animation posted by NASA's Jet Propulsion Laboratory, which manages the rover.

Read more