New Addition to the Exoplanetary Menu: The WASP-12b Sizzler

The hotspot: A very, very hot Jupiter has been discovered (ESA/C Carreau)
The hotspot: A very, very hot Jupiter has been discovered (ESA/C Carreau)

So how hot is the hottest known planet? Usually the temperature of a planet orbiting another star is of little concern to us. At the end of the day, are we really looking for an interstellar getaway? The chance that we’ll be colonizing any extra-solar planets in the near future is pretty low, but that won’t stop us from peering up the the heavens studying “Hot Jupiters” orbiting stars hundreds of light years away. However, astronomers have just discovered a planet I doubt we’ll ever want to visit. Enter WASP-12b, the hottest, and fastest gas giant ever observed…

The SuperWASP observatory (the UK’s Wide Area Search for Planets) is split between two locations. SuperWASP-North can be found in the stunning Canary Islands off the coast of Africa, and SuperWASP-South has the southern hemisphere covered in South Africa. Both observatories have an array of eight wide-angle cameras keeping a watchful eye on the skies. Automatically, SuperWASP looks out for the periodic dimming of the stars as companion exoplanets pass in front of (or “transit”) the points of light. So far the system has discovered 15 exoplanets, but one of them, orbiting a star called WASP-12, stands out as being a little odd.

WASP-12b orbits its host star once every (Earth) day. This means that it must be orbiting the star pretty damn close. This speedy planet orbits the star at a distance 1/40th of Earth’s orbital radius around the Sun; it is therefore approximately 0.025AU from the surface of WASP-12 (when you compare that distance with Mercury’s closest approach of the Sun – 0.3AU – you can imagine how hot it must be on this extreme planet).

SuperWASP-North robotic cameras pointing skywards (SWASP)
SuperWASP-North robotic cameras pointing skywards (SWASP)

It turns out that this planet is in fact a gas giant, 1.5 times the mass of Jupiter, but it has a diameter 1.8 times larger than Jupiter. The extreme heating caused by the close proximity to its star has caused the gas giant to swell up much bigger than it should be. Its surface temperature has been estimated to be 2250°C, that’s 200°C hotter than the previous record holder HD 149026b.

The strange thing is that this toasted planet shouldn’t be there. According to standard planetary theory, gas giants such as WASP-12b evolve in the outer regions of star systems and they gradually migrate closer and find a stable orbit at a safe distance from their host star. WASP-12b however ignored this rule and slipped into a lower orbit than expected.

This is an amazing discovery of the most extreme exoplanets ever observed. It’s fast, hot and it breaks all the rules; it’s the kind of place I’d love to visit… well, from 1AU away at least…

For more about this record-breaking discovery, read “Hottest Ever Exoplanet Discovered: WASP-12b


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