A dominant theory about planets has been challenged by the discovery of nine worlds transiting distant stars, astronomers reported on Tuesday.
The belief that planets always orbit their sun in the same direction, imitating the rotation of the star itself, has been turned upside down, they said.
"This is a real bomb we are dropping into the field of exoplanets," said Geneva Observatory astronomer Amaury Triaud, referring to planets outside the Solar System.
Triaud's team are to report their findings at a meeting this week of the Royal Astronomical Society (RAS) in Glasgow, Scotland. Their revolutionary notion is based on the discovery of nine exoplanets, which bring the tally of these phenomena to a grand 452 since they first came to light in 1995.
The latest planets are especially useful, as they were not discovered indirectly — by calculating their gravitational pull on the star's light — but because they passed directly in front of the sun.These rarely-captured 'transit' events are especially coveted, for they can yield much more information about the planet.
After combining the new results with previous observations of transiting exoplanets, Triaud and fellow astronomers Andrew Cameron and veteran exoplanet hunter Didier Queloz were stunned.Six of 27 exoplanets they sampled were found to orbit in the opposite direction of their host star.
The big hypothesis about planets is that they coalesce from a disc of dust and gas orbiting a young star and move in the same direction of the star's own rotation.
"The new results really challenge the convention wisdom that planets should always orbit in the same direction as their stars spin," said Cameron, of the University of St Andrews, Edinburgh.