Astronomers detect signature of hydroxyl molecule in exoplanet atmosphere – sciencedaily

An international collaboration of astronomers led by a researcher from the Center for Astrobiology and Queen’s University Belfast, and including researchers from Trinity College Dublin, has detected a new chemical signature in the atmosphere of an extrasolar planet ( a planet that orbits a star other than our Sun).

The hydroxyl radical (OH) was found on the day side of the exoplanet WASP-33b. This planet is a so-called “ super-hot Jupiter ”, a giant gas planet orbiting its host star much closer than Mercury orbiting the Sun and thus reaching atmospheric temperatures of over 2,500 ° C ( hot enough to melt most metals).

Principal investigator based at the Center for Astrobiology and Queen’s University Belfast, Dr Stevanus Nugroho, said: “This is the first direct evidence of OH in the atmosphere of a planet beyond solar system. This not only shows that astronomers can detect this molecule in exoplanet atmospheres, but also that they can begin to understand the detailed chemistry of this planetary population. “

In the Earth’s atmosphere, OH is mainly produced by the reaction of water vapor with atomic oxygen. It is a so called “atmospheric detergent” and plays a crucial role in the Earth’s atmosphere to purge polluting gases which can be dangerous to life (eg methane, carbon monoxide).

In a much hotter and larger planet like WASP-33b, where astronomers have already detected signs of iron and titanium oxide gas) OH plays a key role in determining the chemistry of the atmosphere through interactions with water vapor and carbon monoxide. It is believed that most of the OH in the atmosphere of WASP-33b was produced by the destruction of water vapor due to the extremely high temperature.

“We only see a temporary and weak signal of water vapor in our data, which would support the idea that water is being destroyed to form hydroxyl in this extreme environment,” Dr Ernst explained. de Mooij of Queen’s University Belfast, co-author on this study.

To make this discovery, the team used the infrared Doppler (IRD) instrument at the Subaru 8.2-meter-diameter telescope located in the Maunakea summit area in Hawaii (approximately 4,200 m above the level of the sea). This new instrument can detect atoms and molecules through their “spectral fingerprints”, unique sets of dark absorption characteristics superimposed on the rainbow of colors (or spectrum) emitted by stars and planets.

As the planet revolves around its host star, its speed relative to Earth changes over time. Just as the siren of an ambulance or the roar of the engine of a racing car changes tone as it passes in front of us, the frequencies of light (eg, color) of these spectral footprints change with the speed of the planet. This allows us to separate the planet’s signal from its bright host star, which normally overwhelms such observations, although modern telescopes are nowhere near powerful enough to take direct images of these “ hot Jupiter ” exoplanets. .

Dr Neale Gibson, assistant professor at Trinity College Dublin and co-author of this work, said: “The science of extrasolar planets is relatively new, and a key goal of modern astronomy is to explore atmospheres in detail. of these planets and eventually to search for “Earth-like” exoplanets – planets like ours. Each new atmospheric species discovered further improves our understanding of exoplanets and the techniques needed to study their atmospheres, and brings us closer to that goal. “

By taking advantage of IRD’s unique capabilities, astronomers were able to detect the tiny hydroxyl signal in the planet’s atmosphere. “The IRD is the best instrument for studying the atmosphere of an exoplanet in the infrared”, adds Professor Motohide Tamura, one of the main researchers at IRD, director of the center for astrobiology and co-author of this work.

“These atmospheric characterization techniques for exoplanets are still only applicable to very hot planets, but we would like to further develop instruments and techniques that allow us to apply these methods to colder planets, and ultimately to a second Earth. “says Dr Hajime Kawahara, assistant professor at the University of Tokyo and co-author of this book.

Professor Chris Watson of Queen’s University Belfast, co-author of this study, continues: “Although WASP-33b may be a giant planet, these observations are the test bed for next-generation installations like the Thirty-Meter Telescope and the European Extremely Large Telescope in the search for biosignatures on smaller and potentially rocky worlds, which could provide clues to one of humanity’s oldest questions: “Are we alone? ” “

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