What WASP-69b’s Comet-Like Tail Tells Us About Hot Exoplanets

New research on exoplanet WASP-69b has a comet-like tail of hydrogen and helium. The planet is so close to its host star that stellar winds are blowing off large amounts of its atmosphere. This discovery was conducted using the Keck Observatory’s NIRSPEC instrument, and may help astronomers understand exoplanet formation. The new findings have been outlined in a paper published in The Astrophysical Journal in January.

An artist impression of a hot exoplanet orbiting close to its host star. Gas giants that orbit close to their star are more vulnerable to losing atmospheric mass due to stellar winds. Credit: ESA/ATG medialab, CC BY-SA 3.0 IGO.

Exoplanet WASP-69b, a “Hot Jupiter”

WASP-69b is a gas giant exoplanet with a diameter slightly larger than Jupiter but a mass less than a third of Jupiter. It is often referred to as a “hot Jupiter” because of its compositional similarities to the gas giant and proximity to its host star. WASP-69b is located a mere 0.04525 AU from its star, making its orbit only 3.9 days long. This closeness is what allows the exoplanet to be around the same size as Jupiter, despite only being 0.29 Jupiter masses. The heat from its host star gives more energy to the gases the planet is comprised of, allowing it to expand.

Because the gases that makeup WASP-69b’s atmosphere are not as compressed as the gas giants in our solar system, material from its atmosphere can escape much more easily. Previous observations of the planet suggested that it is losing some atmosphere…