Backwards Planets: Reverse Orbits Explained

Posted by on May 16th, 2011


They call them hot Jupiters. A series of gas giant planets in far off solar systems that appear to circle their star in two very peculiar ways. First, it swings perilously close. Second, a quarter of them seemingly do it backwards compared to the normal orbit behavior.

But how the so called “flipped hot Jupiters” come to be is fascinating. In essence they begin like our own Jupiter, as a gas giant further out in the solar system. At some point, they come in contact with a larger planet whose orbit is so similar it eventually begins to “interact tidally”:

This tidal squeezing is like friction, dissipating energy and causing the planet’s orbit to shrink.

Sometimes, while this process is happening, the orientation of planet’s orbit can be shifted so it’s not in the same plane as the other planets. Occasionally, the orbit can be changed so much it completely flips around.

“We saw this for the first time because we did the calculation much more carefully than people had ever done before,” Rasio said. “The basic physics is just Newtonian mechanics. All of that comes out naturally of simply calculating these very tiny gradual changes that build on.”



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