I read somewhere that an exoplanet in the name of HAT-P-7B orbits its star backwards.Why?


And why did we consider our orbital movement to be forward?Is there some scientific reason to consider the movement as forward?


1 Answer 1


All the planets in the solar system orbit the same way. This is not a coincidence. Planets all form from the same protoplanetary disc that surrounded the young sun. The particles in the disc orbited the same way as the sun rotates, and the planets continue to orbit in the same direction.

In this context forward means orbiting in the same direction as the star rotates. We would expect most planets to orbit "forwards" for the same reason that all the planets in the solar system orbit forwards.

What probably happened with HAT-P-7b is that it was thrown into an odd orbit following a close encounter with another planet, or perhaps another star. It is also conceivable that it is a captured rogue planet. See a New Scientist article about the planet

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    $\begingroup$ Anything that orbited retrograde inn the protoplanetary nebula would experience gravitational interactions that slowed it down. Majority rules. It's the same effect which produces an ecliptic disk. $\endgroup$ May 13, 2018 at 14:35

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