Water is on exoplanets, but there’s not a lot

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Led by the University of Cambridge, researchers have recently conducted the most extensive survey of atmospheric chemical compositions of exoplanets, revealing implications for the search for water.

Researchers used atmospheric data from 19 exoplanets to gather measurements of their chemical and thermal conditions. Ranging from ‘mini Neptunes’ (10 times the mass of Earth) to ‘super Jupiters’ (600 times the mass of Earth) the exoplanets involved in this study spanned a wide range of sizes and environments. As with the giant planet is our solar system, the larger planets were rich in hydrogen, but obit different star types.

The research team found that while water vapour is common in the atmospheres of a wide number of exoplanets, the amount of water discovered surprised researchers as there was much less than predicted.

“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,” said project leader Dr Nikku Madhusudhan from the Institute of Astronomy at Cambridge.

The amount of carbon in our solar system relative to hydrogen in the atmospheres of giant exoplanets is significantly higher than that of the sun. The ‘super-solar’ abundance is thought to have originated when the planets were being formed and large amounts of ice, rocks and other particles were brought into the planet in the process called accretion.

Abundances of other elements have been predicted to be almost as high in the atmospheres of giant exoplanets, especially oxygen, which is the most abundant element in the entire universe, after hydrogen and helium.

“It is incredible to see such low water abundances in the atmospheres of a broad range of planets orbiting a variety of stars,” said Madhusudhan.

“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.

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