What planet has a highly eccentric orbit and crosses the orbit of another planet?

1 Answer
Feb 17, 2017

Nothing we now call a "planet" does this. Pluto is the best known object to cross the orbit of a planet (Neptune), but now it is a dwarf planet.


Pluto's crossing the orbit of Neptune is far from unique. Many Kuiper Belt objects do so, and this commonality is one reason Pluto no longer stands out as a full-fledged "planet" in our classification scheme. We've updated the classification scheme based on better knowledge of the outer parts of the Solar System.

Yet none of these crossing objects will collide with Neptune because Neptune acts in conjunction with the Sun to regulate the orbits of the Kuiper Belt objects. One form of this regulation is orbital resonance, where the smaller object makes a whole number of orbits in exactly the same time as the larger one makes the same or a different whole number of orbits. This keeps the objects spaced apart and thus avoids unwelcome encounters. Pluto, for instance, makes two orbits in exactly the same time that Neptune makes three.

Neptune serving as the "host" for orbit-crossing objects isn't unique either. Our own Earth has similar, albeit fewer, orbit-crossing objects in resonant orbits, like the asteroid 3753 Cruithne. Likewise for other planets.