AAS Nova
Hot Jupiter
A gas giant orbiting closer to its star than Mercury does to the Sun.
The first exoplanet found around a Sun-like star, 51 Pegasi b in 1995, was a Jupiter-mass planet with a four-day year. Nobody had predicted such a thing: giant planets were supposed to form far out, where it is cold enough for ice. The resolution is that they do form far out, and then migrate inward through the disc they were born in. Hot Jupiters are rare in absolute terms but wildly over-represented in discovery catalogues, because they are the easiest planets to detect by both major methods — large, close, and quick to repeat. Their day sides can exceed 2,000°C, hot enough to vaporise iron into the atmosphere.
Where it has come up lately
Related terms
Transit method
Finding planets by watching a star dim slightly as one passes in front.
Radial velocity
Finding planets by the wobble they induce in their star's motion.
Habitable zone
The orbital band where a planet could hold liquid water — no more than that.
Sub-Neptune
The most common kind of planet in the galaxy, and there is not one in our solar system.
Questions
What is Hot Jupiter?
A gas giant orbiting closer to its star than Mercury does to the Sun.
Why does it matter?
Hot Jupiters are rare in absolute terms but wildly over-represented in discovery catalogues, because they are the easiest planets to detect by both major methods — large, close, and quick to repeat. Their day sides can exceed 2,000°C, hot enough to vaporise iron into the atmosphere.