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The GRAVITY instrument of the ESO's Very Large Telescope Interferometer (VLTI) allowed the first direct observation of an exoplanet by optical interferometry. This method revealed a complex exoplanetary atmosphere with clouds of iron and silicates swirling in a global storm. This technique offers unique possibilities to characterize many exoplanets known to date.
This result was announced today in a letter from the journal Astronomy and Astrophysics of the GRAVITY Collaboration [1], in which they present observations of the exoplanet HR8799e by optical interferometry. The exoplanet was discovered in 2010 in orbit around the main sequence star HR8799, located about 129 light-years from Earth in the constellation Pegasus.
The result today, which reveals the new features of the HR8799e, required an instrument with a very high resolution and sensitivity. GRAVITY can use the four telescopes of the ESO VLT to mimic a larger telescope using a technique called interferometry. [2]. This creates a super-telescope – the VLTI – that accurately collects and separates light from the atmosphere of HR8799e and the light from its parent star [3].
HR8799e is a "super-Jupiter", an unparalleled world in our solar system, which is both more massive and much younger than any other planet orbiting the Sun. At only 30 million years old, this exoplanet baby is young enough to give scientists a window into the formation of planets and planetary systems. The exoplanet is totally inhospitable – the energy that remains of its formation and the powerful greenhouse effect HR8799e reach a hostile temperature of about 1000 ° C.
This is the first time that optical interferometry has been used to reveal the details of an exoplanet, and the new technique provides an extremely detailed spectrum of unprecedented quality, ten times more detailed than previous observations. The team's measurements revealed the composition of the atmosphere of HR8799e, which contained surprises.
"Our analysis showed that HR8799e had an atmosphere containing a lot more carbon monoxide than methane, which is not expected from the chemistry at equilibrium," says team leader Sylvestre Lacour, a researcher with CNRS at Paris Observatory – PSL and the Max Planck Institute for Extraterrestrial Physics. "We can better explain this surprising result with high vertical winds in the atmosphere preventing carbon monoxide from reacting with hydrogen to form methane.
The team discovered that the atmosphere also contained clouds of iron and silicate dust. Combined with the excess carbon monoxide, this suggests that the atmosphere of the HR8799e is engaged in a huge and violent storm.
"Our observations suggest a ball of gas illuminated from the inside, with rays of warm light swirling through stormy patches of dark clouds," says Lacour. "The convection moves around clouds of silicate particles and iron, which disintegrate and rain inside.This depicts the dynamic atmosphere of a giant exoplanet at birth, subject complex physical and chemical processes. "
This result builds on GRAVITY's many impressive breakthroughs, including breakthroughs such as last year's swirling gas observation at 30% of the speed of light just outside the horizon. events of the huge black hole located at the galactic center. It also adds a new way to observe exoplanets to the already considerable arsenal of methods available for ESO telescopes and instruments – paving the way for many other impressive discoveries. [4].
Remarks
[1] GRAVITY was developed by a collaboration of the Max Planck Institute for Extraterrestrial Physics (Germany) and LESIA Paris Observatory-PSL / CNRS / Sorbonne University / Univ. Paris Diderot and IPAG of the University Grenoble Alpes / CNRS (France), the Max Planck Institute of Astronomy (Germany), the University of Cologne (Germany), the CENTRA / Centro de Astrofisica e Gravitação (Portugal) and ESO.
[2] Interferometry is a technique that allows astronomers to create a super-telescope by combining several smaller telescopes. The ESO VLTI is an interferometric telescope created by combining at least two of the Unit Telescopes (TU) of the very large telescope or the four smaller auxiliary telescopes. While each UT has an impressive 8.2m primary mirror, its combination creates a telescope with a resolution power 25 times greater than that of an isolated observer observing alone.
[3] Exoplanets can be observed using many different methods. Some are indirect, such as the radial velocity method used by the ESO HARPS instrument, an exoplanet hunter, which measures the attraction exerted by the planet on its parent star. Direct methods, like the technique developed to achieve this result, involve observing the planet itself instead of its effect on its parent star.
[4] Among the exoplanet findings recently made with ESO telescopes include the successful discovery of a Barnard star, the star closest to our Sun, orbiting the Earth, and the ALMA's discovery of young planets orbiting a children's star, using another innovative planet detection technique.
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