Theoretical Planets Are Starting To Stack Up In The Outer Solar System

You may remember that about a year and a half ago, I wrote about a theoretical ninth planet way out in the outer solar system. It's thought to be an ice giant, just like Uranus and Neptune, and to orbit hundreds of AU away. If anything, that theory has gained evidence over the past 17 months. This is not about that planet. This is about a new theoretical planet orbiting in the outer solar system. Yes, if it turns out that both these planets actually exist, we'll have ten planets.

Credit: Heather Roper/Lunar and Planetary Laboratory

So, what's the story with Planet Ten? Why do we need it? Simple, it all comes down to those pesky Kuiper Belt objects again. They're not behaving the way they should be, their orbits are not in alignment with the plane of the solar system. Something is moving them, and it isn't Planet Nine, which is too far away to have the observed effect. So now we have Planet Ten, thought to be much smaller than its theoretical sibling, weighing in somewhere between Earth and Mars and looking essentially like a giant Pluto. Also, Planet Ten orbits much closer to the sun than Planet Nine, to the tune of several dozen AU rather than several hundred. So actually, Planet Ten would be the ninth planet, and Planet Nine would be the tenth planet, and that's not going to be confusing at all.

I wouldn't worry too much about having to memorize two new planet names any time soon though. It's easier to find planets around other stars than to find them around our own at this point. These planets, if they do exist, will move incredibly slowly, and give off almost no light at all. As the article says, we'll see what happens when the Large Synoptic Survey Telescope is finished and starts searching for KPOs. Until then, there's still only eight planets.

A Ninth Planet for Our Solar System?

Yes, that's right, after 10 years, the International Astronomical Society have realized their mistake and are reinstating Pluto as the ninth planet. It's a controversial decision in the astronomical world, but the IAU has recognized the public popularity of Pluto, especially after the New Horizons visit, and astronomers now feel that an exemption should be made for Pluto.

Uhhh, no. Did I have you going? Probably not.

So, yes, scientists have announced that there is likely a large body very far out in the solar system, hundreds of AU away. It obviously isn't official yet, but this is some very interesting news. The hypothetical planet would likely be about 10 times more massive than the Earth and would orbit about 20 times further away then Neptune. The evidence for the existence of this object, since we haven't actually seen anything, is that the orbits of 6 Kuiper Belt objects seem to be heavily influenced by something. The orbits all point in the same general direction, even though the objects, including the dwarf planet Sedna, are moving at very different speeds.

If you recall your astronomical history, you'll remember that the search for Neptune commenced because of perceived inconsistencies in Uranus' orbit, and that the search for Pluto occurred because of inconsistencies in Uranus' and Neptune's orbits. So, as with most extraordinary discoveries, it's important not to jump to any conclusions. But I do find it interesting that a few months back, scientists hypothesized the existence of a fifth gas giant in the early solar system which was cast out due to interactions from an early Jupiter or Saturn. This hypothetical planet would have been an ice giant, like Uranus and Neptune. The new "Ninth Planet" is also almost certainly an ice giant which probably did not form that far out in the solar system. Interesting how this works out, isn't it? I'm expecting to hear more about this in the future.