On summer days, we sometimes complain that it’s hot enough to fry eggs on the sidewalk, the car, or any other exposed surface. On some planets in other star systems, though, it’s hot enough to vaporize the eggs, the sidewalk, and even the car. In fact, astronomers have discovered vaporized iron, nickel, and other metals in the atmospheres of several exoplanets.

All of these planets are giants — at least as big as Jupiter, the giant of our own solar system. That means they’re big balls of gas. And the planets are all quite close to their parent stars — no more than a few percent of the distance from Earth to the Sun.

At such close range, the atmospheres of these planets are heated to thousands of degrees. That means their daytime skies are free of clouds or hazes. On some of them, though, clouds may form on the nightside, where it’s cooler.

One planet where it’s too hot for clouds even at night is KELT-9b. It’s the hottest planet yet seen, with temperatures of more than 7,000 degrees. That causes the atmosphere to puff up, making KELT-9b about three times wider than Jupiter.

By watching as the planet passes in front of its star, allowing starlight to filter through the atmosphere, astronomers have measured what’s in the atmosphere. The list of elements includes iron, titanium, and chromium. It also includes a couple of “rare-earth” elements — scandium and yttrium — more metals for a blazing-hot planet.

Script by Damond Benningfield

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