An explanation for the presence of molecular oxygen on the comet 67P/Churyumov-Gerasimenko

Scheme of the molecular oxygen production process (Image courtesy Caltech)
Scheme of the molecular oxygen production process (Image courtesy Caltech)

An article published in the journal “Nature Communications” provides an explanation for the presence of oxygen molecules on the comet 67P/Churyumov-Gerasimenko. Konstantinos Giapis, a chemical engineer at Caltech, conducted this research after noting that the chemical reactions that took place on the comet’s surface were similar to those he had been generating for years. The most likely hypothesis initially offered was that it had “survived” since the solar system’s formation but perhaps the correct explanation has now been found.

The announcement of the discovery of molecular oxygen – O2 – in the comet 67P/Churyumov-Gerasimenko’s coma by ESA’s Rosetta space probe came with an article published in the magazine “Nature” in October 2015. It was a surprise because O2 is very reactive so it tends to combine, for example with hydrogen to form water. The researchers discarded various possible reactions as sources of that oxygen ending up considering likely for those molecules to have been somehow imprisoned in the comet since the solar system’s formation.

Research didn’t stop because there were doubts about the mechanisms that could hold a considerable amount of molecular oxygen for 4.6 billion years. Now a possible explanation came from Konstantinos Giapis, a chemical engineer who normally works on developing processes for microprocessor manufacturing. He might seem to be the least suitable person to conduct a research on a comet but this could be one of those cases where the knowledge accumulated in a scientific discipline turns out to be useful in a very different one.

Konstantinos Giapis seems to know the importance of not keeping isolated in his field because he stated he started getting interested in space looking for places where ions can be accelerated against surfaces. This led him to getting interested to ESA’s Rosetta mission and when he read data on the energies of the water molecules that struck the comet, everything clicked. In essence, he saw that what was happening on 67P/Churyumov-Gerasimenko was similar to what he had been studying for years.

Along with his colleague Yunxi Yao, Konstantinos Giapis verified in his lab what process can be responsible for the constant production of O2 on the comet 67P/Churyumov-Gerasimenko. It’s an abiotic process, which means it involves no life forms, so it can take place in that kind of environment. This mechanism is of the type called Eley-Rideal, a reaction that occurs when high speed molecules collide with a surface extracting atoms to form new molecules in three steps.

In the first step water vapor is emitted by the comet 67P/Churyumov-Gerasimenko due to solar heat, in the second step the water molecules are ionized by ultraviolet solar radiation and in the third step the ionized molecules are pushed by the solar wind towards the surface where they collide with materials containing oxygen acquiring an atom of this element that allows to generate the O2.

When the O2 was discovered in the comet 67P/Churyumov-Gerasimenko’s coma, a correlation was also found with the presence of water with the same ratio between the two molecules at different areas of the comet. If O2 is actually produced from water that’s not a mere correlation but a cause-effect relationship. The researchers were surprised by that discovery but Konstantinos Giapis’s theory explains it.

If this explanation is confirmed, it means that the O2 on the comet 67P/Churyumov-Gerasimenko is produced continuously, at least when it’s close enough to the Sun. The mechanism proposed by Konstantinos Giapis may also work on exoplanets, one of the possible reactions that could release oxygen in an atmosphere with no life forms. In the past, the presence of oxygen was considered a possible indicator of the existence of life forms but the discovery of new possible abiotic reactions is affecting exoplanet studies.

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