The planet WASP-69 b was recently brought to light thanks to a surprising discovery: it has a “queue” of gas, leaving behind an atmospheric trail. This unique feature reveals that the planet is gradually losing its atmosphere, made up of light particles of hydrogen and helium that escape from the external atmosphere.
Tail formation mechanisms
THE “Hot Jupiters” like WASP-69 b, gigantic gas planets very close to their star, undergo a phenomenon called photoévaporation. When stellar radiation heats the outer atmosphere of these planets, light gases are heated and propelled into space. The star of WASP-69 b thus erodes the planet’s atmosphere over time.
The stellar winda continuous flow of charged particles emitted by the outer atmosphere of the star, plays a key role in the configuration of this gas escape by forming an exoplanetary tail. This stellar wind therefore shapes the escaping gas into a tail that unfolds at the rear of the planet.
Impact of stellar wind on the tail
The size and shape of the tail can vary depending on the intensity of the stellar wind. As Dakotah Tyler, an astrophysicist at the University of California, Los Angeles and lead author of the study, explains, if the stellar wind decreasesthe escaping atmosphere might not form a tail, remaining spherical and symmetrical. Conversely, a stronger stellar wind would sculpt this atmosphere into a more structured tail, similar to a “windsock”.
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Observations and discoveries
The research team observed that WASP-69 b’s tail extended more than 7.5 times the radius of the planetor more than 350 000 miles. This measurement is, however, considered a lower limit, as observations were stopped before the tail signal completely disappeared.
Consequences of gas loss
Despite the significant loss of gas — approximately 200,000 tons per second — WASP-69 b is losing its atmosphere at a very slow rate. Estimatedly, every billion years, it loses a mass of gas equivalent to that of the Earth. Given that its solar system is about 7 billion years old, the planet has already lost seven Earths’ worth of gas.
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Scientific relevance of the discovery
This study offers valuable insights into the interactions between planetary and stellar atmospheres, as well as the behavior of stellar winds. THE exoplanetary tailsinfluenced by stellar activity, could also serve as indicators of the behavior of stars over time.
Published in “The Astrophysical Journal” in January 2024, this research led by Dakotah Tyler and carried out with the help of the Keck/NIRSPEC NIRSPEC spectrograph, opens new avenues for understanding the complex dynamics of planetary and stellar systems, thus enriching our knowledge of the universe.
