Water Common On Large Exoplanet, But It's Far From Abundant

Artist's impression of a hot Jupiter. ESO/L. Calçada

Water is a crucial feature of our planet and the life on it. Therefore, it is only reasonable to look for this important molecule elsewhere in the cosmos, especially when it comes to exoplanets. New research highlights that water is indeed common in large exoplanets but is scarcer than models predict.

A team of scientists looked at the atmospheric composition of 19 exoplanets ranging in size from a mini-Neptune, 10 times the mass of our planet, to a super-Jupiter weighing over 600 times the Earth. As reported in The Astrophysical Journal Letters, water vapor was detected in 14 of those exoplanets but there was a lot less than expected. By comparison, the presence of elements such as potassium or sodium in six planets respectively was very much in line with expectations.

“We are seeing the first signs of chemical patterns in extra-terrestrial worlds, and we’re seeing just how diverse they can be in terms of their chemical compositions,” project leader Dr Nikku Madhusudhan, from the Institute of Astronomy at the University of Cambridge, said in a statement.

Dr Madhusudhan was in the team that first measured water vapor in giant exoplanets five years ago, and since then researchers have been gaining more and more insights into their properties. The findings suggest that chemical elements cannot be assumed to be equally abundant in planetary atmospheres following established models. There is more going on.

In our Solar System, the giant planets have a lot more carbon than the Sun, most likely because ice, rocks, and other particles played a role in their formation. This was believed to apply to exoplanet gas giants too, but the study suggests that this is not the case, which has some interesting consequences for planetary formation theories in general.

“Measuring the abundances of these chemicals in exoplanetary atmospheres is something extraordinary, considering that we have not been able to do the same for giant planets in our Solar System yet, including Jupiter, our nearest gas giant neighbour,” said Luis Welbanks, lead author of the study and PhD student at the Institute of Astronomy.

The team plans to look at more planets to see if this scarcity of water is common or not. They are hoping to detect more elements and molecules in those distant atmospheres.

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