hot-jupiters

KELT-9b has a dayside temperature of about 4,600 K, as hot as a K-type star. It is one of thousands of exoplanets whose conditions force astronomers to invent new atmospheric chemistry: iron that condenses on a night side, glass-forming haze, orbits measured in hours, and worlds with no star at all. Here is what the records actually say, and what they do not.

In 2022, the James Webb Space Telescope returned the first clear, detailed evidence of carbon dioxide in a planet outside the solar system. The same planet later gave up sulfur dioxide made by starlight chemistry, water, carbon monoxide, sodium, and potassium, and showed that its morning and evening edges differ.

Planets do not always stay where they form. Torques from the gas disk around a young star, resonances between planets, and later gravitational scattering can all shift orbits. Migration explains hot Jupiters, tightly packed super-Earths, and possibly Mars's small size.