The Sciences

Exoplanets of the Week: A "Diamond Planet" and Gas Giant Quadruplets

80beatsBy Jennifer WelshDec 9, 2010 12:02 AM


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A couple of new exoplanets are leaving researchers scratching their heads in confusion. So bright, so vivid! So prismatic!

A planet called WASP-12b is the first planet that's been found to have more carbon than oxygen in its atmosphere, unlike most planets in our solar system. In the paper published in Nature, researchers suggest that the gas giant probably has a carbon-based core. And all that carbon has set the researchers eyes a-sparkle with possibilities:

The researchers say their discovery supports the idea there may be carbon-rich, rocky planets whose terrains are made up of diamonds or graphite. "You might see land masses and mountains made up of diamonds," [said] lead researcher Dr Nikku Madhusudhan. [BBC News]

The alien planet was discovered in 2009 and is about 870 light-years away. It's about 1.4 times as massive as Jupiter and sits just 2 percent as far from its parent star as the Earth is from the sun. Sadly, we can't go mining there, since the hypothetical diamonds are surrounded by the gas giant's scorching atmosphere (4,200 degrees Fahrenheit) of hydrogen. Even if you got down to its rocky core, any diamonds would likely be mixed in with graphite and even liquid carbon.

"This study shows that there is this extreme diversity out there," study lead author Nikku Madhusudhan, now of Princeton University, told "Fifteen years or so since the discovery of the first exoplanet, we're just beginning to appreciate how different they can be." []

If future researchers find small, rocky planets with similar compositions that are farther from their suns, those planets could have surfaces of carbon compounds, unlike of Earth's silica-based rocks. Madhusudhan explains that such planets would look very strange to us:

"That would mean that in the mountains, a large fraction of the rock mass could instead be made of diamonds and lots of land masses rich in diamonds, much more than we see on Earth." These planets would be lacking in water. So, if temperatures were sufficiently high, liquid on their surface would consist of carbon-rich compounds, such as tar, he says. [BBC News]

The exceedingly different chemistry on such strange new worlds could lead to extremely different life forms, like critters that thrive on carbon-rich methane and don't require oxygen or water. Gas giants breaking the (theoretical) rules

Researchers have just discovered a fourth planet

orbiting the HR 8799 star system. This system now has four monstrous gas giants (each five to thirteen times the size of our measly Jupiter) located 14.5, 24, 38, and 68 times farther from their star than the Earth is from the sun. Because the planets are all so similar, their layout in the star system is messing with researcher's ideas of how planets form, they report

this week in Nature. Neither of their traditional models for planetary formation--core accretion and disc instability--can account for the odd spacing. The core accretion model proposes that gas giants can form when dust collects into a rocky core, which then attracts gas to create the atmosphere. But HR 8799's farthest-out planet couldn't have formed by accretion, because at that distance its velocity in orbit is too slow for dust to quickly build up into a planetary core. By the time a core had formed, the researchers say, the gases that would have made up its atmosphere would have blown away. The newfound, innermost planet in the system also throws a wrench in the other model, disc instability. In this model, the disc of dust and gas that spins around a young star can suddenly collapse in places to form a proto-planet. But the new planet orbits about 15 times farther from its sun than the Earth does from Sol, a location where the sun's heat and the fast rotation of the disc would prevent the collapse required to create a planet. These two puzzling planets make researchers suspect that there's more to the story than they can see now.

It is unlikely that a mixture of the two processes would have produced planets with such similar masses, they say. Instead, the planets may have formed further in or out and then migrated through the gassy disc to their current positions. [New Scientist]

Related content: 80beats: Astronomers Find a Bevy of Exoplanets; Won’t Discuss Most Interesting Ones

80beats: Astronomers Predict a Bonanza of Earth-Sized Exoplanets

Bad Astronomy: Gallery of exoplanets: real pictures of alien worlds

(gallery) Visual Science: Astronomer Mike Brown on Arty Exoplanets

(gallery) DISCOVER: How to Settle, Once and for All, the Whole "What's a Planet?" Debate

DISCOVER: The Freakiest Places in the Solar System

(gallery) Images: (1) NASA/JPL-Caltech/R. Hurt (SSC) and (2) 2MASS/UMass/IPAC-Caltech/NASA/NSF/NRC-HIA & C. Marois

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