Observe the evaporation of atmospheric helium from a giant planet

It has been predicted for more than 15 years that helium would be one of the most easily detectable gases in giant exoplanets. The reason is clear, helium is the second most common element in the universe, after hydrogen; and it is also one of the main constituents of the planets Jupiter and Saturn in our Solar System. However, the detection of helium in exoplanets is not an easy task.

The study that is now published in Science and that is signed by researchers of different nationalities, among them scientists from the Center for Astrobiology (CAB, CSIC-INTA), has managed to detect the elusive helium in the atmosphere of the giant exoplaneta WASP-69b and obtain information about the speed of the helium atoms that they abandon the planet's gravitational field and the length of the tail they produce.

The detection was possible thanks to the CARMENES instrument, a spectral spectrograph of high spectral resolution developed by a consortium of German and Spanish institutes, among which is the Astrobiology Center. CARMENES was initially designed to detect exoplanets and not to investigate their atmospheres, so this finding "has been a very pleasant surprise and makes the instrument one of the world leaders in exoplanetary sciences", comments José Antonio Caballero, CAB researcher and co-author of the study.

In addition to this finding, the study also includes the analysis of four other planets of similar size. These are the hot exoplanets HD189733b and HD209458b, which have a mass similar to that of Jupiter the extremely hot giant planet KELT-9b and the warm exoplanet GJ463b, the size of Neptune. The analysis does not show helium exospheres around the last three, which challenges the previous theoretical predictions. The warm Jupiter HD189733b, on the other hand, shows a strong absorption of helium, although in this case it does not form a tail but a wrap around the planet. "Not only do we see the helium line, we can also explain the physical reasons why it is detected on some planets and why not on the others, due to the intense high energy radiation (X-rays and extreme ultraviolet radiation). coming from the star, if it does not reach enough intensity you can not see the line ", explains Jorge Sanz Forcada, CAB researcher and co-author of the study. The detection of the helium line "opens an important window for the study of the outer layers of atmospheres of low-density planets, allowing a better physical characterization of the planetary systems neighboring ours," says María Rosa Zapatero Osorio, CAB researcher and member of the research team.

This new line of study will allow to astrophysicists dedicated to the characterization of exoplanet atmospheres compare, in the coming years, the processes of evaporation in a wide sample of planets; and answering questions like their planets with an ultra-short orbital period are, in reality, evaporated cores of ancient hot Jupiters.

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Figure: artistic representation of WASP-69b in which the tail is observed planetary formed by helium particles. © Gabriel Pérez Díaz (IAC)

 

Fuente: UCC-CAB

 

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