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Second backwards planet 'discovered'

world Updated: Aug 14, 2009 13:45 IST

Astronomers have discovered a second exoplanet orbiting its star backwards, a day after the first "retrograde" exoplanet was spotted.

Using the Japanese Subaru telescope to observe planet HAT-P-7b, two teams, one led by Joshua Winn of MIT and another led by Norio Narita at the National Astronomical Observatory of Japan, have discovered the second exoplanet.

"It is funny that the two good cases for really misaligned orbits, even retrograde orbits, have come at around the same time.

"We don't know if it's a slowly rotating star that we're seeing edge-on, or a really rapidly rotating star that we're seeing pole-on. It could be like the solar system -- but reversed, or it could be going pole over pole. Either way it's cool," Winn said.

However, both the teams disagree on the tilt of the exoplanet's orbit.

While the US team's measurements indicate that the planet either runs backwards along the star's equator, at a tilt of about 180°, or it orbits the star's poles, at a 90° tilt, the Japanese team claimed that the orbit is inclined by 227° with respect to the star's equator.

"Statistically, they're highly discrepant. It could be due to differences in how the two teams used the telescope, or in the models they used to interpret their findings. They will not know for certain until they can exchange their data," Winn was quoted by the 'New Scientist' as saying.