Hubble reveals egg-shaped exoplanet so hot it's venting vaporized iron into space
Between exoplanets with ruby clouds and those that are actually just giant diamonds, science fiction has barely prepared us for just how weird alien worlds could be. Now, thanks to new Hubble observations we have another contender in WASP-121b, a planet that's so intensely hot it's vaporizing heavy metals and venting them into space. As if that wasn't enough, the poor planet is also being stretched into an egg shape thanks to the strong gravity of its host star.
WASP-121b was discovered back in 2015, and its searing temperatures have been a known feature since then. But this exoplanet is hot even among its class of so-called "Hot Jupiters," with temperatures in the upper atmosphere reaching a blistering 2,538° C (4,600° F). That's roughly 10 times hotter than that of any other known planet.
And now Hubble has looked a bit closer and spotted a strange new side effect of this incredible heat. Using its Space Telescope Imaging Spectrograph instrument, the team studied the planet's atmosphere. As WASP-121b passes in front of the star, astronomers can measure the wavelengths of light that filter through the atmosphere, giving them an indication of what kinds of gases are present and in what amounts. By focusing in on the ultraviolet light, the team could make out the signatures of heavy metals like magnesium and iron.
This isn't particularly surprising news on its own, but the unexpected thing was just how high up those metals were. In fact, they were escaping from the exoplanet's atmosphere entirely, venting into space.
"Heavy metals have been seen in other hot Jupiters before, but only in the lower atmosphere," says David Sing, lead researcher on the study. "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.
"We were mainly looking for magnesium, but there have been hints of iron in the atmospheres of other exoplanets. It was a surprise, though, to see it so clearly in the data and at such great altitudes so far away from the planet. The heavy metals are escaping partly because the planet is so big and puffy that its gravity is relatively weak. This is a planet being actively stripped of its atmosphere."
WASP-121b is under so much stress because it's orbiting extremely close to its host star, completing a "year" every 1.27 days. That would make for a toasty planet in our solar system, but it just so happens this star is far hotter and brighter than our Sun. To cap it all off, the intense gravity of this tight orbit is pulling the planet into a football shape.
The weird world of WASP-121b is one to watch, and the team says that the soon-to-be-launched James Webb Space Telescope could help with that. Since it focuses on infrared light, this could search for water and carbon dioxide in the atmosphere. After all, Hubble has previously found the glowing evidence of water in this incredibly hot atmosphere.
The research was published in the Astronomical Journal.