Non-periodic comets are comets which have very long orbital periods (>200 years or more), spending most of their time in the outer solar system.

Planet X, recently revived by researchers at Caltech, is a proposed planet orbiting in the farthest reaches of the outer solar system. The Caltech researchers infer its presence from to its effect on the orbits of Kuiper belt objects.

If such a planet exists, and is the cause of the Kuiper belt object alignments, could it not also knock such objects in to the inner solar system, creating non-periodic comets with huge aphelion orbital distances? Could our current observations of non-periodic comets be used to infer properties of the planet?


1 Answer 1


The idea is basically to look for comets coming from the same direction. Look for a pair of comets that at some time earlier in their orbit was at the same place at the same time. That is a data point, but an extremely inaccurate one. It does not have to mean anything, and you are going to collect a large amount of statistical noise. For this purpose, normal periodic comets are close to useless, as they are in the same region for decades or even centuries as they fall slowly towards the sun. Hyperbolic (non-periodic) comets on the other hand, have a shorter stay in each region, allowing us to better pin-point a possible encounter. The problem is, there are not actually a lot of them observed, and the length of the time horizon for accurate enough observations is not that long.

The properties you can obtain about the ninth planet, if it exists, from large amount of data on non-periodic comets are:

  1. Current distance within a reasonably large error margin. (+-10 AU)

  2. Orbital period; not so accurate, but you may get an OK estimate.

  3. Inclination; not accurate, but together with the orbital period, estimates will grow more accurate over a longer time horizon of observations.


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