Earlier observations suggested only a small or non-existent tail.
Scientists have identified a fascinating phenomenon in space: a giant gas tail extending over 350,000 miles behind the exoplanet WASP-69 b. This massive feature, similar to a comet’s tail, provides an unprecedented opportunity to study the interactions between exoplanetary atmospheres and their host stars, shedding light on the evolution of gas giants.
WASP-69 b, located approximately 160 light-years from Earth, is a gas giant similar in size to Jupiter but significantly less massive. It orbits a star at a blisteringly close distance, completing one orbit every 3.9 days. This extreme proximity subjects the planet to intense stellar radiation and powerful stellar winds, which strip its atmosphere over time.
The exoplanet’s atmosphere is currently losing an estimated 200,000 tons of gas every second, primarily helium with traces of hydrogen. Over its 7-billion-year lifetime, this process could have reduced the planet’s mass by an amount equivalent to seven Earths. Recent observations using the W. M. Keck Observatory in Hawaii confirmed that this escaping gas forms a spectacular tail stretching 350,000 miles—44 times Earth’s diameter.
How the Tail Is Formed
The tail results from stellar wind—a stream of charged particles emitted by the planet’s host star. As gas escapes from WASP-69 b’s overheated atmosphere, the wind sculpts it into a long trail stretching behind the planet. Without this wind, the gas would disperse symmetrically around the planet.
“Earlier observations suggested only a small or non-existent tail,” explained Dakotah Tyler, the study’s lead author. “Our findings confirm that WASP-69 b’s helium tail extends at least seven times the planet’s radius.”
This phenomenon not only reveals how gas giants evolve but also serves as a natural tool for measuring stellar winds. By studying the tail’s structure, scientists can infer the properties of the stellar wind shaping it.
“When the planet’s escaping atmosphere collides with stellar wind, the interaction sweeps the gas into a distinctive tail,” said Erik Petigura, a UCLA physics and astronomy professor. “These features allow us to analyze these interactions in unprecedented detail.”
The discovery of WASP-69 b’s giant tail deepens our understanding of how gas giants form and evolve in hostile environments. It also highlights the dynamic relationship between planets and their stars, offering a new perspective on planetary atmospheres across the galaxy.
