Tenth planet is a term formally applied to the possible Planets beyond Neptune, before the reclassification of Pluto.

In this sense there are planets beyond Neptune and Pluto-but they are not nearly as big as the Jovian planets, or even Pluto.

Discrepancies in the early 1900s between the observed and expected orbits of Uranus and Neptune suggested that there were one or more additional planets beyond Neptune.

In 1909, Thomas Jefferson Jackson See, an astronomer with a reputation as an egocentric contrarian, opined "that there is certainly one, most likely two and possibly three planets beyond Neptune".

Most astronomers refer to a region of small planets beyond Neptune as the "Kuiper belt", since Kuiper had suggested that such small planets or comets may have formed there.

For a short list of notable asteroids, see list of notable asteroids, and for notable minor planets beyond Neptune's orbit, see trans-Neptunian object and list of plutoid candidates.

The three planets beyond Neptune would escape roasting, but were unsuitable for other reasons, The two outermost would remain glacial, and, moreover, lay beyond the range of the imperfect etherships of the Eighth Men.

Two papers by Rawlins and Max Hammerton (University of Cambridge) produced upper limits on the gravitationally permissible masses of planets beyond Neptune, showing that exterior planets at probable distances were far from giant, suggesting that the main bodies of the solar system may end at Neptune.