Figure 1: Artist's rendition of the HAT-P-7 system. Researchers used rhe 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 Enlarge
Astronomers have used the Subaru Telescope to show that the HAT-P-7 planetary system, which is about 1040 light years from Earth in the constellation Cygnus, includes at least two giant planets and one companion star (Figure 1). 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 of the retrograde planet HAT-P-7b offer new insights into how retrograde planets may form and endure.
A Japanese collaboration led by Norio Narita (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.
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