Hot Jupiters are gas giants that orbit close to their stars, making them vulnerable to a process known as photoevaporation. The intense radiation heats their atmospheres, causing lightweight gases to escape. On WASP-69 b, this escaping gas is further sculpted by the stellar wind - a constant stream of charged particles flowing from the star's corona.
Lead author Dakotah Tyler, an astrophysicist at UCLA, explained, "Strong stellar winds can sculpt that outflow in tails that trail behind the planet," comparing the phenomenon to a comet's tail. The gaseous tail of WASP-69 b stretches at least 7.5 times the planet's radius, exceeding 350,000 miles, though the true length could be greater due to observational limits.
This tail's shape and size are influenced by variations in the stellar wind. Tyler likened the process to a windsock, which takes on a structured form when wind intensity increases. Without the stellar wind, the escaping gas would spread more symmetrically around the planet.
WASP-69 b's tail is illuminated by starlight, making it visible for observation, but changes in stellar activity could alter the tail's appearance. This phenomenon provides valuable insights into stellar behavior and the interactions between stellar winds and planetary atmospheres.
The exoplanet loses about 200,000 tons of atmospheric gas per second, but the process is gradual enough that the planet remains intact. Over its estimated 7-billion-year lifespan, WASP-69 b has lost atmospheric mass equivalent to seven Earths, a testament to the slow but steady effect of photoevaporation and stellar wind interactions.
The findings were published in January 2024 in The Astrophysical Journal. The study, led by Dakotah Tyler, is titled "WASP-69b's Escaping Envelope Is Confined to a Tail Extending at Least 7 Rp," and is based on observations made using Keck/NIRSPEC.
Research Report:WASP-69b's Escaping Envelope Is Confined to a Tail Extending at Least 7 Rp
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