The tenth planet of the solar system (often called Planet X) is one of those searches in astronomy that drifts in and out of popular notice. No tenth planet has been discovered yet (and there might not even be a ninth since Pluto's status as a planet is under debate, since it is so small and acts more like Kuiper Belt object than a planet), but here is a basic summery: Back in the 19th century irregularities were noticed in the orbit of Neptune that many explained as being the result of a massive unseen ninth (Pluto wasn't found till the 1930's) planet. They searched and searched and searched, but didn't find anything. It during this search that Pluto was found, but it is definietly not big enough to have the effect they were looking for, so some still think there is a planet out there we just haven't found yet. It is possible that the planet might have a very low albedo (the percentage of light a planetary body reflects back into space) and being that far out (around 40 AU or more) it would be very dim and hard to detect. Now I couldn't tell you whether the irregularities in Neptune's orbit have been solved or not, but I don't think so as they are still looking for Planet X and this seems to be the main reason why. Hope this helps you out, and feel free to email me if you have any further astronomical questions.

-Paul

: I've heard there was a 10th planet discovered in our solar system and am trying to find some information about the planet for the elementary class I assistant teach.

: Is this information correct? Where can I find more about the planet?

: Thanks in advance for your help! : Becky

• Planet X = Black Hole? - aberka - February 20, 2002 - 14:15 UTC