Breathing in on Mars

Take a deep breath, and while you exhale slowly, think about what has just happened: you have inhaled a few litres of Earth’s atmosphere, we call it air. Could you have taken that same breath on Mars?

Well, you probably would have fainted very, very quickly because there are important differences between Earth’s and Mars’ atmosphere. For a start, there is the pressure of the atmosphere: 1013 mbar here on Earth, 6 mbar on Mars – that’s at ‘sea level’ or the Martian equivalent thereof. From that alone you can see that the two atmospheres are very different, and the Martian atmosphere is too thin to breathe for humans. 

But there are chemical differences, too. The Earth’s atmosphere has 78 % nitrogen as its main constituent, and the next most abundant element is oxygen at 21 %. Carbon dioxide is a trace gas, as scientists call it, which means there is much less than one percent of it in the terrestrial atmosphere. Comparing that to Mars reveals a stark difference: Carbon dioxide makes up 95 % of the Martian atmosphere! Nitrogen is the second most abundant element at 2.6 %. And oxygen? Well, the element so important to our breathing – and a lot of life on Earth – is only a trace gas on Mars. Therefore, it is not just the fact that the Martian atmosphere is so thin, it also does not have the amounts of oxygen future astronauts would need. 

The thin atmosphere means, future astronauts would have to wear spacesuits every time they want to leave their habitat. But they would also have to protect themselves from the intense cold at the surface. The fact that the atmosphere is so thin means, it cannot keep the planet warm. While temperatures can rise up to 20 °C during a summer day, a lot of that warmth gets lost to space as soon as the sun goes down. The lowest temperature can be as low as -153 °C, and the average temperature is around -80 °C. It depends a little on the location, and of course what the season is, too, but one thing is clear: it’s cold! For comparison, the coldest temperature ever recoded on Earth was measured in Antarctica, and it was ‘just’ -93 °C°. Thus, any future astronauts would need a spacesuit that provides them with the air to breathe and the warmth to keep their bodies alive.

While you have taken your breath, you might have looked up to the sky and noticed some clouds, maybe they were so thick that all you could see was grey, or there were big white fluffy clouds, or maybe thin cirrus clouds? Cloud formation is an atmospheric phenomenon that is dependent on the composition, thickness and movements of the atmosphere. With Mars’ thin atmosphere, we would not expect rain clouds or big white clouds, but that does not mean there no clouds! The very first detection goes back to the NASA Pathfinder mission in 1997. The NASA Curiosity rover, currently exploring Gale Crater, has captured clouds many times. I really like the image of clouds over Mont Mercou, a cliff face in Gale Crater on Mars. The image has been taken on 19^th March 2021 here on Earth, Curiosity’s 3063^rd Martian day. 

Image credit: NASA/JPL

This image was taken by the Mastcamera on the Curiosity rover on sol 3063, Curiosity’s 3063rd day on Mars. It shows clouds over a cliff face, called Mont Mercou, at Gale Crater. The rover was making its way up Mt. Sharp, the central feature in Gale crater, climbing past this cliff face and investigating the rocks on the way. More about the discovery is here: Curiosity Spots Clouds Over Mont Mercou | NASA Jet Propulsion Laboratory (JPL)

Curiosity most recently took a 17 minute sequence of images, which resulted in a beautiful timelapse of so called noctilucent (night-glowing) clouds. We do have those on Earth, too, they appear just after sunset, when a very thing layer of clouds is illuminated from below. Enjoy the view, for more information, see here: NASA’s Curiosity Rover Captures Colorful Clouds Drifting Over Mars | NASA Jet Propulsion Laboratory (JPL).

Image credit: NASA/JPL

This image is a time lapse of images taken over 17 minutes at Gale Crater, Mars, by the Curiosity rover.

Beyond cloud imaging, the Curiosity rover has investigated the Martian atmosphere with its SAM (full name Sample Analyser at Mars, but we rarely say that out loud!) instrument. One investigation that instrument has carried out was to look for methane. Methane is quite famous as it could be an indicator that microbes were living there. But before we jump to a conclusion, we need to know that there are many other ways to make methane, microbes do not have a monopoly on that! Rocks can do it too. All we need is the mineral olivine, which is commonly found on Mars, and some hot water. As hot water has circulated the curst on Mars in the past – and maybe is still today – when new impact craters formed and when volcanoes such as the big Olympus Mons were active. The reaction between the water and the mineral olivine would have released hydrogen, and that could have reacted with the carbon dioxide from the atmosphere to form methane. With that, we have to conclude that all we need to make methane is rocks, and the question still stands: Have microbes ever contributed to methane on Mars?

We don’t know that yet, but maybe we are about to find out. The Perseverance rover, currently exploring Jezero crater on Mars, is collecting samples that a mission designed by the two space agencies NASA and ESA in collaboration will bring to Earth. It is called ‘Mars Sample Return’ (Mars Sample Return - Mars Missions - NASA Jet Propulsion Laboratory | NASA Jet Propulsion Laboratory (JPL)). In the set of samples deposited at ‘Three Forks’ (Perseverance's 'Three Forks' Sample Depot Map - NASA Science), there also is one sample tube that only contains the Martian atmosphere, so we can investigate it with the laboratories here on Earth. That will give us detailed insights into the chemistry of the atmosphere on the day of sampling, but it will also allow us to compare that atmosphere with the gases trapped in the other sample tubes alongside the rocks and soils that were collected. Will that tell us, if there ever was life on Mars? Maybe, but before we can even start to think about that, astrobiologists need to find out a lot more about microbes, their interactions with rock, the traces they leave and the ways to find them. And that is what we do here at AstrobiologyOU (AstrobiologyOU | Addressing the scientific, governance and ethical challenges associated with astrobiology.). Meanwhile, teams of scientists, including AstrobiologyOU researchers, are also thinking about that returned sample of Martian atmosphere, how much gas it will be and what we could investigate with it (The value of returning a sample of the Martian atmosphere | PNAS).