Is It A Planet? Exotic Object Orbiting Star Stirs Exoplanet Classification Rethink

By | October 9, 2008

The European spacecraft COROT has discovered a massive planet-sized object orbiting its parent star closely, unlike anything ever spotted before. It is so exotic, that scientists are unsure as to whether this oddity is actually a planet or a failed star.

The object, named COROT-exo-3b, is about the size of Jupiter, but packs more than 20 times the mass. It takes only 4 days and 6 hours to orbit its parent star, which is slightly larger than the Sun.

COROT-exo-3b was found as the satellite observed the drop in the brightness of the star each time the object (COROT-exo-3b) passed in front. “We were taken by surprise when we found this massive object orbiting so close to its parent star”, said Dr Magali Deleuil from the Laboratoire d’Astrophysique de Marseille (LAM), leader of the team that made the discovery. She added, “COROT-exo-3b is really unique – we’re still debating its nature.”

The search for planets with orbital periods less than 10 days orbiting close to the parent star has lasted almost 15 years. During this time, scientists have encountered planets with masses 12 times that of Jupiter, and stars 70 times as massive as Jupiter, but none in between. This is why the 20-Jupiter-mass COROT-exo-3b was such a surprise.

This odd find does not fall into either conventional category of planets or brown dwarfs. A brown dwarf is a ‘failed star’, a sub-stellar object that is not undergoing nuclear fusion at its core, but displays some stellar characteristics.

“COROT-exo-3b might turn out to be a rare object found by sheer luck”, said Dr Francois Bouchy, from Institut d’Astrophysique de Paris (IAP), member of the team that made the discovery. “But it might just be a member of a new-found family of very massive planets that encircle stars more massive than our Sun. We’re now beginning to think that the more massive the star, the more massive the planet,” he said. – sd

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