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The carbon planet

Artist's impression of WASP 12b

Artist's impression of WASP 12b, a giant planet 1,200 light-years from Earth. It has more carbon than oxygen.

PLANETS SUCH AS EARTH have more oxygen than carbon, but what if the composition was reversed?

This is a question opened up by a recent discovery of a ‘diamond planet’ by US and UK scientists, led by Nikku Madhusudhan of the Massachusetts Institute of Technology, and including researchers from Belfast’s Queens University and the University of Warwick.

The planet is 1,200 light years away from Earth and was observed using NASA’s Spitzer Space Telescope.

Dr Marek Kukula of the Royal Greenwich Observatory in London, whose role is to interpret and comment on astronomical discoveries made by British scientists, explained that researchers initially used the SuperWASP (Wide Angle Search for Planets) robotic observatories operating continuously, all year around.

They detected the planet, then it was observed with the Spitzer Space telescope, which according to Dr Kukula “detected the heat coming from the planet, and from that heat signature they can tell what this planet is made from.”

Artist's impression of WASP 12b

WASP 12b strange nature suggests there's more than one way to make a planet.

Giant planet

The planet is very different to Earth.

“It’s a giant planet,” explains Dr Kukula, “a gas planet, a bit like Jupiter in our Solar System.”

“But the interesting thing that they’ve discovered is that it has a very different composition to the planets in our Solar System,” he adds. “So where our planets have a half fraction of oxygen then carbon, this planet has it the other way around, it has more carbon than oxygen.”

This suggests that there is more than one way to make a planetary system and the range of planets in the Universe could be much wider than previously thought.

Diamonds and graphite

Dr Kukula says that if there are smaller planets in the same planetary system with a similar composition, rich in carbon, their rocks could be rich in minerals such as carbon and diamonds, unlike Earth which has silica, the sand that rocks on Earth are made from.

“This is where this diamond planet idea comes from, they haven’t actually detected a diamond planet yet,” explains Dr Kukula.

It’s hypothetical, “but you can imagine bizarre landscapes with black graphite rocks lying around and the surface could be covered with tarry liquids rather than water.”

Adapted from information issued by The British Council / NASA / STScI / G. Bacon.

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Diamond life for distant planet

Artist's concept of planet WASP-12b

Artist's concept of the searing-hot gas planet WASP-12b (orange orb) and its star. Scientists have discovered that the planet has more carbon than oxygen, making it the first carbon-rich planet ever observed. Astronomers say that carbon-rich gas planets could have abundant diamond in their interiors.

  • Planet WASP-12b is 1,200 light-years from Earth
  • Most carbon-rich planet yet discovered
  • Daytime temperature is hot enough to melt steel

ASTRONOMERS HAVE DISCOVERED that a huge, searing-hot planet orbiting another star is loaded with an unusual amount of carbon.

The planet, a gas giant named WASP-12b, is the first carbon-rich world ever observed.

The discovery was made using NASA’s Spitzer Space Telescope, along with previously published ground-based observations.

“This planet reveals the astounding diversity of worlds out there,” said Nikku Madhusudhan of the Massachusetts Institute of Technology, Cambridge, lead author of a report in the December 9 issue of the journal Nature. “Carbon-rich planets would be exotic in every way—formation, interiors and atmospheres.”

It’s possible that WASP-12b might harbour graphite, diamond, or even a more exotic form of carbon in its interior, beneath its gaseous layers.

Astronomers don’t currently have the technology to observe the cores of exoplanets (ie. planets orbiting stars beyond our Sun) but their theories hint at these intriguing possibilities.

The research also supports theories that carbon-rich rocky planets much less massive than WASP-12b could exist around other stars. Our Earth has rocks like quartz and feldspar, which are made of silicon and oxygen plus other elements. A carbon-rich rocky planet could be a very different place.

“A carbon-dominated terrestrial world could have lots of pure carbon rocks, like diamond or graphite, as well as carbon compounds like tar,” said Joseph Harrington of the University of Central Florida, in Orlando, who is the principal investigator of the research.

Mountains made of diamond

Carbon is a common component of planetary systems and a key ingredient of life on Earth. Astronomers often measure carbon-to-oxygen ratios to get an idea of a star’s chemistry. Our Sun has a carbon-to-oxygen ratio of about one to two, which means it has about half as much carbon as oxygen.

Spitzer plot of molecules in atmosphere of WASP-12b

Data from NASA's Spitzer Space Telescope indicates that the atmosphere of planet WASP-12b has carbon monoxide, excess methane, and not much water vapour. The results demonstrate that WASP-12b is the first known carbon-rich planet.

WASP-12b is the first planet ever to have its carbon-to-oxygen ratio measured at greater than one (the actual ratio is most likely between one and two). This means the planet has excess carbon, some of which is in the form of atmospheric methane.

“When the relative amount of carbon gets that high, it’s as though you flip a switch, and everything changes,” said Marc Kuchner, an astronomer at NASA Goddard Space Flight Centre, who helped develop the theory of carbon-rich rocky planets but is not associated with the study.

“If something like this had happened on Earth, your expensive engagement ring would be made of glass, which would be rare, and the mountains would all be made of diamonds.”

WASP-12b derives its name from the consortium that found it, the Wide Angle Search for Planets. It is 1.4 times as massive as Jupiter and located roughly 1,200 light-years away from Earth.

This blistering world whips around its star in a little over a day, with one side always facing the star. It is so close to its star that the star’s gravity stretches the planet into an egg-like shape. What’s more, the star’s gravity is siphoning mass off the planet into a thin disc that orbits around with it.

The Spitzer data also reveal more information about WASP-12b’s temperature. The world was already known to be one of the hottest exoplanets found so far; the new observations indicate that the side that faces the star is 2,300 degrees Celsius. That’s more than hot enough to melt steel.

Adapted from information issued by NASA / JPL. Images courtesy NASA / JPL-Caltech / N. Madhusudhan (Princeton University).

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