Indian finds 'diamond' planet - Computation by BHU alumnus points to carbon-rich body

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By G.S. MUDUR
  • Published 9.12.10
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An artist’s impression of the extremely hot exotic planet (right) and its host star. Credit: NASA/JPL-Caltech/R Hurt
Madhusudan Nikku

New Delhi, Dec. 8: An Indian scientist has helped discover a giant planet rich in carbon orbiting a distant star, an exotic world that forecasts rocky planets where diamonds may be as common as sand on Earth.

Madhusudan Nikku, a Banaras Hindu University alumnus now at Princeton University in the US, and his colleagues have observed that an extremely hot planet discovered a year ago has as much carbon as oxygen — a feature never observed on a planet until now.

The planet, Wasp 12b, orbits a star about 1200 light years away from the Sun and appears to have temperatures of nearly 2300°C — hot enough to melt stainless steel — and an atmosphere loaded with carbon monoxide, methane, and traces of water.

The findings will appear in the journal Nature tomorrow.

“A carbon-rich planet has dramatic implications for its interior, its atmosphere, and may compel us to rethink our long-ingrained ideas of planetary formation,” said Madhusudhan, who is a postdoctoral scientist in the department of astrophysical sciences at Princeton.

The planets in the solar system are believed to have formed when tiny planetesimals, made up of grains of dust and water-ice, were pulled towards each other by gravitation. The water-ice leads to a high abundance of oxygen in the solar system. The Sun itself has a carbon-to-oxygen ratio of 0.54 — indicating that the early solar system had a lot more oxygen than observed on Wasp12b.

“The question Wasp12b throws up is if the planetesimals there weren’t made of water-ice, what could have produced a carbon-rich planet” Madhusudan said. Scientists are speculating that tiny particles of tar could have served as seeds for carbon-rich planets.

While Wasp12b itself is a gas giant with no hard surface — similar to Jupiter — scientists say its discovery supports the possibility that similar rocky exoplanets could have crusts made up of silicon and carbon, instead of silicon and oxygen found on Earth.

“We could imagine carbon-rich planets whose crusts are made of graphite or diamond — and where sand (silicon and oxygen) may be as rare as diamonds are on Earth,” Madhusudan told The Telegraph in an interview.

Scientists used Nasa’s Spitzer Space Telescope to observe light emitted by the planet Wasp12, discovered in 2009 by researchers in the UK-based consortium called Wide Angle Search for Planets (Wasp). A computational technique developed two years ago by Madhusudan while he was at the Massachusetts Institute of Technology was used to analyse the atmosphere of the planet.

“The origin of the carbon-rich atmosphere is a mystery — the planet exemplifies the huge diversity possible in exoplanet atmosphere composition,” said Sara Seager, a planetary scientist at the Massachusetts Institute of Technology.

“But I want to emphasise that just because the atmosphere is carbon-rich, does not mean that the interior is carbon-rich, although this is an intriguing possibility,” said Seager, who had with a colleague Marc Kuchner predicted the possibility of carbon-rich planets back in 2005.

Researchers believe carbon-rich planets will also pose new questions for astrobiologists.

“A carbon-rich planet, even one lying within the habitable zone of a star, would have little oxygen, not enough water, and a surface dominated by methane,” Madhusudan said. “You would have to ask what sort of biology would such an environment support.”

The carbon-rich environment of Wasp12b is also difficult to explain because its parent star, Wasp12, appears to have the same carbon-to-oxygen ratio as the Sun. “If the parent star is not carbon-rich, then the planet must have formed elsewhere and was captured by this star,” said Sujan Sengupta, a scientist at the Indian Institute of Astrophysics, Bangalore.

“If it wasn’t captured, our current theories of planetary formation get in trouble,” Sengupta told The Telegraph. “Under our current theories, a star and planets are formed from the same primordial material and the abundances of elements should be nearly the same.”