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Poor astronomy | The carbon-13 isotope has been depleted on Mars and may be due to geology, astronomy or biology

NASA rover Curiosity has been driving around Mars for almost a decade now, over 3,300 Mars days. It has studied the environment in Gale Crater, a huge impact element over 150 kilometers wide. Billions of years ago, Gale was probably a lake of water, and it was chosen as a landing site specifically for Curiosity to study the conditions there and see if they could ever have supported life.

It's not directly looking for small green Martian animals, but it's come up with something of a mystery. A possible - possible - The solution is life, but do not skip the gun. It is still possible that abiotic (non-biological) processes are responsible for the anomaly.

Curiosity has a drilling machine on board that allows it to dig into rocks on the surface, and the samples can then be analyzed using a mass spectrometer, a device that can determine the amount of different chemicals in the sample. For example, it can look at how much carbon dioxide, methane, carbon monoxide and other molecules are present relative to each other.

It can also look at isotopes of some elements. A single element, like carbon, is defined by having six protons in the nucleus of its atoms. If it also has 6 neutrons, it is called carbon-12 (abbreviated 12C). If it has 7 neutrons, it is carbon-13 (13C). These different isotope of carbon can tell you different things about the origin and evolution over time of a sample because they have slightly different properties.

For example, Mars' atmosphere has a relationship of 12C to 13C at about 78 to 1. It is actually slightly lower than the natural ratio of these isotopes elsewhere. Why? 12C is lighter than 13C (by the weight of a neutron). Some processes in Mars' atmosphere give these atoms energy, and for the same amount of energy one 12C-atom will have a higher velocity than 13C because it is lighter. At the top of the atmosphere it means 12C is more easily lost to space, increasing the ratio 13C to 12C.

This is where the strangeness comes in (link to paper). Curiosity has taken 30 different samples at five different locations on the surface of Mars inside Gale Crater, and the relationship between 13C to 12C varies greatly from place to place. But in almost all cases, this ratio is lower than it is in the atmosphere.

In other words, some process on Mars is either lowering the amount of 13C or reinforcing the amount of 12C.

The researchers who conducted this study offer three plausible mechanisms for doing this. One is that ultraviolet light from the Sun can separate carbon dioxide molecules in Mars' upper atmosphere into carbon monoxide and an oxygen atom, which then recombines with other molecules to form more complex carbon-based molecules. These processes can very little favor the lighter weight 12C atoms, so that when these molecules fall to the surface, they become incorporated into the rock, increasing the amount of 12C in relation to 13C.

Another possibility - and I like this one for obvious reasons - is that the Sun now and again, about every 100 million years or so on average, plows through a cloud of interstellar gas and dust, called a giant molecular cloud. Interstellar dust falls on Earth all the time, but during one of these cloud passes, that number can increase up to 100 times! It's still a little bit in all, but as it happens, these clouds have more 12C in them than 13C compared to what we see on Mars. So if this dust rained down to the surface, it would get better again 12C at the expense of 13Cause c.

The third option is the most exciting, but to be completely clear, it is not proven at all. Like the others, it's just an idea: Biology. Ancient Mars bacteria could have produced methane biologically. If that life were like terrestrial bacteria, that methane would preferably have it 12C-atom in it. The methane would then rise into the air, be flung by the sun's ultraviolet light and rain down as in the example above, be incorporated into rocks and increase the amount of 12C contra 13C in them. I would note that strange methane flags have been discovered on Mars, but an explanation for them - geologically or biologically - has not yet been found.

So what is it? Strange chemistry, strange collisions with giant clouds of dust or strange, barking Mars bacteria?

Yes, so that's the problem. It is not possible to say which is the best answer, just that they are all plausible. The researchers in the study are very careful to point out that point, perhaps by the fact that a lot of people in the media will run away with the idea of ​​effervescent bacteria.

It is worth noting that none of these processes work well on Earth, so no matter which one it is, it is strange. Well, compared to what we are used to. But part of studying Mars is trying to figure out how it is different and how these processes unfold.

The real downside is that the evidence right now is very uncertain. It is possible that more samples analyzed by Curiosity may help. The Perseverance Rover is also a few thousand kilometers from Curiosity in the crater Jezero, and it is not only looking for evidence to see if life was supported there for ages ago, but it also looks for life itself, fossilized or otherwise. Even if it does not find any, the samples it analyzes can help break the stalemate.

Until then, the Mystery of the Martian Carbon Isotope Ratios will continue.

Mars, it turns out, is an interesting place. But it does not so easily reveal its secrets. Hopefully with curiosity and perseverance we can just get our answer.

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