Oh, how blasé we've become. Fifteen years ago the discovery of a planet around another star would have been front-page news.
Now the exoplanet tally stands at 334 — with more than 60 of those found this past year alone. To make the news these days, an alien world must either have something in common with Earth (such as water) or be truly bizarre.
So let me introduce you to WASP-12b, the place to go to ward off winter's chill. Discovered earlier this year by the Super Wide-Angle Search for Planets (SuperWASP), this orb has 1.4 times the mass of Jupiter.
But Jupiter-mass exoplanets are as common as Fisher Space Pens at an astronaut reunion. So what's special about this one? Two things.
First, it orbits so close to the host star (0.023 astronomical unit, or about 2 million miles) that it takes just 26 hours to complete one revolution. When exoplanets circle this tightly, they often appear to pass in front of and behind their host stars, and that's precisely how WASP-12b was discovered.
Second, the planet has a diameter 1.79 times that of Jupiter. Run the numbers, and you'll deduce that WASP-12b has a mean density of just 0.3 g/cm3. Now, astronomers are fairly certain that WASP-12b is not a solid sphere of bamboo 160,000 miles across. But they are at a loss to explain why it's so big.
The 12th-magnitude host star, situated some 670 light-years away in southeastern Auriga, is a luminous F dwarf that scalds WASP-12b with light 6,600 times more intense than we get here on Earth. So its cloud-top temperature must be in the vicinity of 2,500 kelvins (nearly 4,600°F).
Simulations suggest that the intense heat should keep the planet puffed up a bit — but nothing like what's observed. So the discovery team, led by Leslie Hebb (University of St. Andrews, Scotland), suspects that the planet is shrouded in energy-absorbing hazes consisting of titanium and vanadium oxides, among the few things that are solid at those temperatures. The exotic dust might be absorbing enough light and heat to puff out the planet's outer layer.
Hebb and her colleagues explore this possibility in a paper to appear in the Astrophysical Journal.
In the meantime, they can claim bragging rights for having found the exoplanet with the largest known diameter (among those that transit), the hottest surface, and the shortest orbital period.