Wednesday , October 20 2021

Research: an exoplanet inflated like a balloon –


Although helium is a rare element on earth, it is everywhere in the universe. It is the main component of the stars and gigantic planets after hydrogen. Despite its abundance, helium was only recently detected in a gigantic atmosphere of gas, by an international team including astronomers from the University of Geneva (UNIGE), Switzerland. This time, the team, led by the Genevan researchers, observed in detail and for the first time saw for the first time how this gas escaped from an over-inflated outer atmosphere with a helium. Results published Science.

Helium is the second most abundant element in the Universe. Since 2000, these planets revolving around stars other than the sun have been predicted as one of the best possible viewers of the atmosphere of the outer planets, and have actually detected astronomers 18 years later. With the very special observational signature of the helium in the infrared, it was difficult for most of the previously used instruments to be out of range. The discovery was made earlier this year thanks to the Hubble Space Telescope observations, which were difficult to interpret. Members of the UNIGE, the members of the National Competency Center in Research Planet, had the idea of ​​pointing to a new telescope (a spectrograph called Carmenes) equipped with a new instrument.

To identify the colors of planets with Carmenes

A spectrograph divides the light of a star into component colors, like a rainbow. The "resolution" of a spectrograph is a measure of the number of colors that can be revealed. Although the human eye cannot discern any color beyond the red color without an adapted camera, the infrared eye of Hubble can identify hundreds of colors there. It was enough to define the color signature of helium. Built on a 4-meter telescope in the Calar Alto Observatory in Andalusia, Spain, Carmenes is able to define more than 100 colors on infrared!

This high spectral resolution allowed the team to monitor the position and speed of the helium atoms in the upper atmosphere of an extra four gigantic Neptune in the size of the earth. In the Cygnus constellation, HAT-P-11b, which is 124 light-years away from the house, is twenty times closer to its star, compared to the Sun 124 hot Neptune-(a good 550 ° C!). Çalış We suspect that this affinity with the star can affect the atmosphere of this outer planet, ini says Romain Allart, a PhD student at UNIGE and the first author of the study. Iyor The new observations are so delicate that the outer atmosphere is undoubtedly inflated by the star's radiation and escaped into space, ler he adds.

A planet inflated with helium

These observations were supported by a numerical simulation led by Vincent Bourrier, co-author of the study and member of the European project FOUR ACES *. Thanks to the simulation, it is possible to track the orbit of helium atoms: 10.000 Helium was blown over the planet by day and night over 10,000 km / h, h says Vincent Bourrier. Ir Because it is such a light gas, it easily escapes from the attraction of the planet and creates an expanded cloud around it. In This gives helium an inflated balloon shape to HAT-P-11b.

This result opens a new window to observe the extreme atmospheric conditions prevailing on the hottest outer planets. The Carmenes observations show that such studies can only be achieved with more precision with the ground-based telescopes equipped with the right kind of tools, with the long thought possible from the space. , These are exciting times for the search of atmospheric signatures on external planets, ler says Christophe Lovis, co-author of the study and senior lecturer at UNIGE. In fact, UNIGE astronomers are heavily involved in the design and use of two new high-definition infrared spectrographs, similar to Carmenes. One of the so-called SPIRou launches an observation campaign from Hawaii, while the UNIGE astronomy division launched the first tests of the Near Infrared Planet Search (NIRPS) to be established in Chile at the end of 2019. The result will increase the interest of the scientific community for these instruments. Their numbers and geographical distribution will allow us to vaporize the entire planet and vaporize the outer planets, ve Lovis adds.

* FOUR ACES, The Future of Upper Atmospheric Characterization of External Planets by Spectroscopy, is a project funded by the European Research Council (ERC) Consolidation grant under the European Associations 2020 Research and Innovation Program (grant grant grant of 724427).


Université de Genève. .

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