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The Hubble Space Telescope has detected an exoplanet that is so hot that it is shedding iron and magnesium out of its upper atmosphere and so close to its host star that tidal forces are stretching it into a shape that vaguely resembles a football. This exoplanet, dubbed WASP-121b, has an upper atmosphere that gets as hot as 4,600 degrees Fahrenheit, hot enough to not only vaporize iron, but also send streams of it into the upper atmosphere, where it can escape the planet by “hitching a ride” on streams of hydrogen and helium.

Heavy Metals Escaping Planet in Rare Phenomenon

WASP-121b is a gaseous planet like Jupiter rather than a “rocky” planet like Earth. Normally, “hot Jupiters” do not get hot enough to shed elements that scientists consider “heavy metals” because they are heavier than hydrogen and helium. Instead, heavy metals that are hot enough to form gases tend to condense into clouds.

“Heavy metals have been seen in other hot Jupiters before, but only in the lower atmosphere,” explained lead researcher David Sing of the Johns Hopkins University in Baltimore, Maryland. “So you don’t know if they are escaping or not. With WASP-121b, we see magnesium and iron gas so far away from the planet that they’re not gravitationally bound. … This is a planet being actively stripped of its atmosphere.”

Although not originally designed to look for exoplanets, Hubble has proven useful for studying the chemical composition of planetary atmospheres once the exoplanets’ existence has been confirmed. Scientists observed the planet using the Hubble Space Telescope’s Space Telescope Imaging Spectrograph to search for the spectral signatures of heavy metals. They focused on magnesium due to a theory that it would be easier to spot escaping the planet, but also detected unexpectedly high iron content in the streams of elements escaping the planet. The upcoming James Webb Telescope may help scientists study water and carbon dioxide content in WASP-121b’s atmosphere.

Interactions With Host Star May Destroy Planet

The escaping metals may actually be contributing to the exceptional heat of WASP-121b’s atmosphere by interacting with ultraviolet light in a way that creates a runaway “greenhouse effect” in addition to the heating caused by being so close to its host star.

The host star is also bigger and hotter than our Sun, giving it extra power to bake the planet. Scientists say that the gravitational forces between the star and the planet are so great that the planet is likely to be torn apart.

“We picked this planet because it is so extreme,” Sing said.

The study was conducted as part of the Panchromatic Comparative Exoplanet Treasury (PanCET) survey, which uses the Hubble Space Telescope to survey 20 exoplanets ranging in size from “super-Earths” to Jupiter-sized planets. The results are published in The Astronomical Journal.