Tuesday, April 13, 2010

Nine new exoplanets found, some with retrograde and highly inclined orbits

Exoplanets, discovered by WASP together with ESO telescopes, that unexpectedly have been found to have retrograde orbits are shown here. In all cases the star is shown to scale, with its rotation axis pointing up and with realistic colours. The exoplanets are shown during the transit of their parent star, just before mid-transit. The last object at the lower right is for comparison and has a “normal” orbital direction. The size of each image is three solar diameters. (Credit: ESO / A. C. Cameron)

Astronomers have discovered nine new transiting exoplanets. Surprisingly, six out of a larger sample of 27 were found to be orbiting in the opposite direction to the rotation of their host star -- the exact reverse of what is seen in our own solar system.

"This is a real bomb we are dropping into the field of exoplanets," says Amaury Triaud, a PhD student at the Geneva Observatory who, with Andrew Cameron and Didier Queloz, leads a major part of the observational campaign.

Planets are thought to form in the disc of gas and dust encircling a young star. This proto-planetary disc rotates in the same direction as the star itself, and up to now it was expected that planets that form from the disc would all orbit in more or less the same plane, and that they would move along their orbits in the same direction as the star's rotation. This is the case for the planets in the Solar System.

After the initial detection of the nine new exoplanets [1] with the Wide Angle Search for Planets (WASP, [2]), the team of astronomers used the HARPS spectrograph on the 3.6-metre ESO telescope at the La Silla observatory in Chile, along with data from the Swiss Euler telescope, also at La Silla, and data from other telescopes to confirm the discoveries and characterise the transiting exoplanets [3] found in both the new and older surveys.

Surprisingly, when the team combined the new data with older observations they found that more than half of all the hot Jupiters [4] studied have orbits that are misaligned with the rotation axis of their parent stars. They even found that six exoplanets in this extended study (of which two are new discoveries) have retrograde motion: they orbit their star in the "wrong" direction. …

Turning planetary theory upside down: Nine new exoplanets found, some with retrograde orbits

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