‘Boiling Hot’ Jupiter-Sized Planet Hides 350,000-Mile-Long Tail

“Hot girl summer” has a different meaning in the cosmos. Astronomers have discovered a Jupiter-sized planet, whose atmosphere is “boiling away” at a rate of 200,000 tons per second because it orbits its blistering hot star so closely, is hiding a 350,000-mile-long tail. The UCLA study is offering new insights into how close-orbiting planets interact with their stars.

Situated about 160 light years from Earth, WASP-69b is classified as a “hot Jupiter” due to its gas giant status and extremely close orbit to its host star. This proximity leads to a scorching experience for the planet, completing an orbit in less than four Earth days, compared to Mercury’s 88-day orbit around our Sun. The intense radiation and stellar winds from its star are stripping away WASP-69b’s atmosphere, creating a tail that stretches for at least 350,000 miles.

“Work by previous groups showed that this planet was losing some of its atmosphere and suggested a subtle tail or perhaps none at all,” says study first author Dakotah Tyler, a UCLA doctoral student, in a media release. “However, we have now definitively detected this tail and shown it to be at least seven times longer than the planet itself.”

In this artist’s video rendering, WASP 69b orbits its star, trailed by a 350,000-mile-long tail of gas. (Credit: Adam Makarenko/W. M. Keck Observatory)

The tail is shaped by the star’s stellar winds, which physically shepherd the escaped gas into a long, thin formation. This phenomenon is crucial in understanding the evolution of planets.

“Over the last decade, we have learned that the majority of stars host a planet that orbits them closer than Mercury orbits our Sun and that the erosion of their atmospheres plays a key role in explaining the types of planets we see today,” explains study co-author Erik Petigura, a professor of physics and astronomy at UCLA. “However, for most known exoplanets, we suspect that the period of atmospheric loss concluded long ago. The WASP-69b system is a gem because we have a rare opportunity to study atmospheric mass-loss in real time and understand the critical physics that shape thousands of other planets.”

The study utilized the 10-meter telescope at the W. M. Keck Observatory in Hawaii, equipped with a high-resolution spectrograph. This allowed for more sensitive observations than previous efforts, revealing the detailed structure of the planet’s escaping atmosphere, primarily composed of hydrogen and helium.

“These comet-like tails are really valuable because they form when the escaping atmosphere of the planet rams into the stellar wind, which causes the gas to be swept back,” details Petigura. “Observing such an extended tail allows us to study these interactions in great detail.”

Despite the dramatic loss of atmosphere, WASP-69b’s future isn’t as bleak as one might think. Tyler reassures that the planet, being about 90 times the mass of Earth, has a large enough reservoir of material to withstand this loss over its lifetime.

This image from the NIRCam (Near-Infrared Camera) instrument on NASA’s James Webb Space Telescope shows the central portion of the star cluster IC 348.
The UCLA study is offering new insights into how close-orbiting planets interact with their stars. (Credit: NASA, ESA, CSA, STScI, K. Luhman (Penn State University), and C. Alves de Oliveira (ESA))

“It’s in no danger of losing its entire atmosphere within the star’s lifetime,” says Tyler.

The resilience of WASP-69b in such a hostile environment serves as a metaphor for the human spirit.

“Despite the multitude of challenges we may face, our capacity to withstand and overcome is often far greater than we realize. Our problems may seem daunting, but like WASP-69b, we have what it takes to continue on,” concludes Tyler.

The study is published in The Astrophysical Journal.

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