Artist’s rendition of the HAT-P-7 system. Researchers used the Subaru Telescope to discover the retrograde planet (nearest the central star), another giant planet (in the foreground), and a companion star (upper right) in this system. // Credit: NAOJ

The origin and maintenance of a retrograde exoplanet

A team of astronomers thinks a companion star and a newly confirmed outer exoplanet could explain a 2008 exoplanet’s “backward” orbit.

By Subaru Telescope Facility, Hilo, Hawaii — Published: January 24, 2013

Astronomers have used the Subaru Telescope to show that the HAT-P-7 planetary system, which is about 1,040 light-years from Earth in the constellation Cygnus, includes at least two giant planets and one companion star. The discovery of a previously unknown companion HAT-P-7B to the central star HAT-P-7 as well as confirmation of another giant planet HAT-P-7c orbiting outside the retrograde planet HAT-P-7b offers new insights into how retrograde planets may form and endure.

A Japanese collaboration led by Norio Narita from the National Astronomical Observatory of Japan used the Subaru Telescope in 2008 to discover the first evidence of a retrograde orbit of an extrasolar planet HAT-P-7b. Although retrograde planets, which have orbits that run counter to the spin of their central stars, are absent in our solar system, they occur in other planetary systems in the universe. However, scientists did not know how such retrograde planets formed.

Read more: The origin and maintenance of a retrograde exoplanet – Astronomy Magazine.

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