Planets X

[mmcirvin]

What with all the approximately Pluto-sized and larger objects being discovered beyond Neptune, it's interesting to revisit the strange history of Planet X, the large, possibly giant trans-Neptunian planet that Pluto was originally supposed to be.

Today it's almost certain that Planet X does not exist, and the anomalies in planetary motion that it was proposed to explain were simply errors. On the other hand, other people have proposed, based on theories of solar system formation, that there could be respectably-sized icy planets lurking even further out in the dark.

Comments

[arsonnick.livejournal.com]

Some believe the real truth about Planet X died with L. Ron Hubbard...But I think Tom Cruise knows more than he's letting on.

[mmcirvin.livejournal.com]

And then there is Planet X, the crackpot version (http://www.badastronomy.com/bad/misc/planetx/index.html).

Ask Daffy Duck.

[pentomino.livejournal.com]

Finding it is easy enough. Just follow the ascending-lettered planets.

[mmcirvin.livejournal.com]

And outer-solar-system observation has marched on since that page was written. Most obviously, more trans-Neptunian icy objects have been discovered, several of which are approximately Pluto-sized (some of these are covered elsewhere on the site). There's also a whole population of Chiron-like objects, called Centaurs, which are probably former Kuiper Belt objects that got deflected inward.

Then there's Sedna, the most interesting one to me, sometimes described as the first member of the Oort Cloud to actually be observed, though it's bigger and has a smaller orbit than most predictions about the Oort Cloud propose. It still wanders amazingly far away at aphelion for such a large planetoid; if you display Sedna's orbit in Celestia, it actually shows up as an easily visible ellipse when you're about a light-year out into interstellar space.

The new "tenth planet", 2003 UB₃₁₃, is interesting in that it's actually pretty bright as these things go (probably both because it's relatively big, and because its size allows it to retain bright frost on its surface); some amateur telescopes should be able to see it. I'd guess it's escaped detection all these years just because its orbit is inclined at 44 degrees and it's way out of the plane of the solar system, so nobody happened to look where it was. Clyde Tombaugh undoubtedly would have found it during the search that revealed Pluto if it were closer to the ecliptic.