Has Kepler (or any other survey) found an exoplanet with a similar orbit as another exoplanet around the same star?

The current IAU definition of a planet requires that "a planet has cleared its neighborhood around its orbit".

Have there been any exoplanet discoveries that bring such a definition into question?

Mathematically, is there anything stopping 2 "planets" from existing in equilibrium in a similar orbit around a single star?

  • $\begingroup$ What do you mean by "similar orbit?" $\endgroup$ Feb 22, 2017 at 4:46
  • $\begingroup$ The IAU definition of "planet" is specific to objects that orbit our sun. They do not attempt to include exoplanets within this classification. $\endgroup$
    – Phiteros
    Feb 22, 2017 at 5:30

1 Answer 1


Two planets sharing their orbit is expected to be a rare configuration. Most configurations of 2 planets in 1 orbit are unstable. Only when one planet is in a Lagrange point of the other, are the orbits stable.

As of now (February 2017), there are no known co-orbital planets. We do know lots of smaller objects co-orbiting with planets (in our own solar system, there are thousands of Trojans in e.g. Jupiter's orbit).

There was a potential detection (Kepler-223), but on closer examination those planets were unlikely to be co-orbital.

  • $\begingroup$ Can't horseshoe orbits not be stable (at least for a long time)? $\endgroup$
    – fibonatic
    Feb 22, 2017 at 12:40
  • $\begingroup$ Sadly, according to Wikipedia, "follow-up study of the system revealed that an alternative configuration, with the four planets having orbital periods in the ratio 8:6:4:3 is better supported by the data" -- i.e. what was thought to be a co-orbital situation appears not to be. en.wikipedia.org/wiki/Kepler-223 $\endgroup$ Feb 22, 2017 at 15:23
  • $\begingroup$ (Fascinating system either way -- 4 planets orbiting a star quite similar to our sun, but all four well inside Mercury's orbital distance!) $\endgroup$ Feb 22, 2017 at 15:25

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