Found: The Most Fanciful New Planet Ever

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Jupiter, left, and WASP-12b

It's easy to go just a little nuts when you're studying exoplanets. Spend enough time investigating the exotic chemistry, composition and environments of newly discovered worlds orbiting distant stars and you can start to believe anything's possible. Little, however, can match the fairy-tale possibilities of WASP-12b.

For one thing, there's the heavy concentration of carbon in its atmosphere. For another, there's the potential for methane-loving life. Oh, and did we mention that vast stretches of land could be made of diamonds? O.K., few scientists — actually, no scientists — believe that those precise conditions prevail on WASP-12b. But new findings about the planet's atmosphere do suggest that such an environment is entirely possible on other worlds — perhaps even in WASP-12b's own solar system.

It was just last year that WASP-12b was discovered by British researchers working in the Wide-Angle Search for Planets consortium — a collaborative whose acronym gave the planet its name. About 1,200 light years from Earth and 1.4 times the mass of Jupiter, the new world is on the smallish side, compared with the some 500 exoplanets that have been discovered since the first one was confirmed in the 1990s, but it otherwise seemed unremarkable.

As described in a new paper in the journal Nature, however, a team led by postdoctoral planet researcher Nikku Madhusudhan of Princeton University and planetary scientist Joe Harrington of the University of Central Florida used NASA's Spitzer Space Telescope to monitor WASP-12b during one of its orbits, particularly in the instants before it passed behind its home star. In those brief moments, the light from the star would flow through the planet's atmosphere, allowing astronomers to study the wavelengths produced and infer the atmosphere's chemical composition. They combined their findings with those taken independently by a telescope based in Hawaii — and that's when they got their surprise.

Typically, the class of planets that includes WASP-12b — which are known to astronomers as extremely hot Jupiters — have atmospheres with a carbon-to-oxygen ratio of about 0.5. In this case, however, there was more than twice the concentration of carbon as usual and almost 100 times more methane than expected.

"It's the first carbon-rich planet ever found," says Madhusudhan. "Now that we've found one, we know there may be a lot more out there."

That has big implications for extraterrestrial biology, since life as we know it is based on carbon, and methane — which is made up of carbon and hydrogen — is a byproduct of metabolism. WASP-12b is too hot for life (again, as we know it) and has no solid surface. But its sibling planets could be a different matter. Solar systems form when clouds of gas and dust swirling around a star begin to coalesce — and later, when rocks and planetesimals that are the result of this process collide and fuse into larger bodies. Since all of the worlds would be made of the same raw stellar material, all of them would have similar chemistry — carbon-rich chemistry, in this case. Some of the planets formed along with WASP-12b could easily be smaller, with rocky formations made not of silica, like Earth's, but of graphite or — given enough time and enough pressure — something much more precious. "On a carbon-rich world, you could have big landforms made of pure diamond," says Madhusudhan.

The planet's carbon-heavy atmosphere could retain heat and light, providing energy for life to get started and thrive. That life would have to survive on comparatively little oxygen and water, and would have to be very tolerant of methane. In some respects, however, those are biological rounding errors, particularly when so many organic elements are in the mix. Remarkable forms of life are turning up all the time in extreme environments on Earth, not least being the recently announced organisms in California's Lake Mono that can survive on arsenic — a substance decidedly toxic to us.

None of this proves that somewhere in the galaxy, exotic, methane-breathing creatures are indeed at large, bounding across diamond landscapes. But the fact that such a possibility, however remote, is being plausibly discussed is a reflection of how little we know of the cosmos — and how much we're beginning to learn.