Australian Scientists Just Found An Exoplanet So Hot It Tears Molecules Apart

Image: NASA/JPL-Caltech/R. Hurt (IPAC)

International and Australian astronomers have discovered the hottest giant exoplanet to date, which is sitting at a balmy 4,327 degrees Celsius (or 4,600 kelvin). The immense, Jupiter-like planetary oven is sitting in orbit of a star whose mercury nudges almost 9,900 degrees Celsius, say the scientists studying it.

As if that wasn't metal enough, and the stellar radiation hitting it is stripping away the atmosphere and tearing apart molecules in the sky.

This finding helps to improve our understanding of planets orbiting massive, hot stars, which has been limited owing to the small number of previous observations.

Thousands of transiting exoplanets are known to exist but only six have been found orbiting hot, A-type stars (which have temperatures of 7,300–10,000 kelvin), and none has been found around even hotter B-type stars. Previously, the hottest known planet (around 3,300 kelvin) was found orbiting a star with a temperature of around 7,430 kelvin.

Scott Gaudi and the team reported the discovery of the Jupiter-mass gas giant called KELT-9b, orbiting a massive star called KELT-9 in Nature. This star has an estimated temperature of around 10,170 kelvin, placing it at the dividing line between A and B-type stars. The researchers measure the planet's dayside temperature to be around 4,600 kelvin, similar to that of K-type dwarf stars.

It's the level of extreme-ultraviolet stellar radiation that the planet receives that is causing its outer atmosphere to be stripped away. Atomic metals in the atmosphere are probably the primary absorbers of the radiation, the researchers say.