Researchers have discovered a huge tail of gas escaping from an exoplanet near Earth. This fascinating structure, measuring almost 560,000 kilometers, is equivalent to 44 times the diameter of our planet. Powered by intense stellar winds, this tail acts as a true “stellar windsock,” providing scientists with a unique opportunity to observe these cosmic phenomena.
A spectacular tail around WASP-69 b
WASP-69 b is a gaseous exoplanet that is about the size of Jupiter, but with a mass a third less. It orbits a star located 160 light years from Earth and completes one revolution around it in just 3.9 days. This proximity to its star generates extreme temperatures, favoring the loss of gas from its atmosphere.
For example, scientists have observed that the planet loses around 200,000 tonnes of gas, mainly helium and hydrogen, every second. This phenomenon of loss of matter could represent up to seven times the mass of the Earth over billions of years.
Since its discovery in 2014, researchers have speculated about the presence of a comet-like tail of gas, made up of the elements escaping from the planet's atmosphere. However, this hypothesis was never confirmed until recently. A study carried out using data collected by the WM Keck Observatory, located in Hawaii, has finally made it possible to prove the existence of a gas trail 560,000 kilometers long, or approximately 44 times the width of the Earth. The results of the study are published in The Astrophysical Journal.
The stellar winds at the origin of the phenomenon
The researchers discovered that this tail forms thanks to the stellar wind, a stream of charged particles continuously emitted by the planet's star. This wind pushes escaped gases from WASP-69 b's atmosphere, creating a tail-like contrail that extends far behind the planet.
Scientists explain that if the winds were to diminish or disappear, the tail would also evaporate, and the gases escaping from the planet would take on a more spherical and symmetrical shape.
« With weaker stellar winds, the exoplanet's atmosphere would continue to dissipate, but without forming a tail “, says Dakotah Tyler, doctoral student in astrophysics at UCLA and lead author of the study. On the other hand, when these winds are powerful, they sculpt the fleeing atmosphere into a long and dramatic tail.
A window into the evolution of exoplanets
The discovery of this tail offers new perspectives on the evolution of gas giants. In particular, it makes it possible to study how these planets lose their atmosphere over time and to explore the complex interactions between stellar winds and the gases that escape from them. By measuring the tail as a “stellar windsock,” astronomers can assess the properties of winds from distant stars.
« These comet-like tails are particularly useful because they form when a planet's atmosphere interacts with stellar wind “, explains Erik Petigura, professor of physics and astronomy at UCLA and co-author of the study. These observations provide a deeper understanding of the forces at work in these extreme environments.
Furthermore, the James-Webb telescope discovers a “vapor world” on a unique exoplanet.
