This planet is spiralling slowly toward its star. Since its discovery, the time between its transits, when it passes in front of its star, has been shrinking by about 29 milliseconds a year. In 2019 a team led by Samuel Yee published new observations that ruled out other explanations. That made WASP-12 the first planetary system where astronomers could be confident an orbit is decaying. The cause is tides: the planet raises a bulge on its star, and friction inside the star slowly drains the planet's orbital energy. At the current rate, the orbit would shrink on a timescale of a few million years.
The SuperWASP team announced the planet in 2008 and titled their paper "the hottest transiting planet yet discovered". It had the largest radius of any transiting planet known then, about 1.8 times Jupiter's, and the shortest orbit, just 1.09 days. The archive lists its equilibrium temperature, the temperature from absorbing starlight alone, at about 2,600 kelvin. It lies roughly 1,400 light-years away.
Its closeness reshapes it. The star's gravity has stretched the planet into an egg shape. In 2010 Hubble spotted metals such as magnesium and sodium in a cloud of gas around the planet. That cloud spills beyond the region where the planet's own gravity holds on to its gas, suggesting material is being pulled away toward the star. In 2017 Hubble measured how much light the planet reflects. The answer was almost none: at most 6.4 percent, darker than fresh asphalt. Researchers think the heat breaks hydrogen molecules apart, leaving an atmosphere of atomic hydrogen and helium that absorbs rather than reflects light.
Some details remain open. The exact fate of the planet depends on how strongly the star absorbs tidal energy, which is inferred from the decay rate rather than measured directly. The 2010 team also saw an unexpected early dip in ultraviolet light and suggested, without confirming, that a disc of stripped gas might sit ahead of the planet.
TerraForge's model, using only mass, orbit and star, classifies it as a gas giant at about 2,560 kelvin with no habitability. Observations agree on the basics, but the model has no way to show the egg shape, the escaping gas or the shrinking orbit that define this world.