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Could our Solar System Have a Planet which is in a Circumpolar Orbit?

-- Paul | January 14, 2020

Question:

Could a small fictitious planet’s orbit theoretically be placed, perpendicular to the ecliptic, such that its perihelion is between Venus’ and Earth’s orbit and its aphelion between Earth’s and Mars’ orbit, without causing trouble? And preferably such that it orbits the Sun in one year, just like Earth?

-- Paul

Answer:

Theoretically, yes, in general a planet can have an orbit that is perpendicular to its host star (called a circumpolar orbit). Unfortunately, that orbit would be unstable over time as orbits which are in the rotational plane of the star and that are synchronized to the star’s rotation (i.e. one day equals one month on the planet) represent the most stable (least amount of energy exchanged between star and planet) orbits. This instability with time makes circumpolar planets highly improbable.

-- Jeff Mangum

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