Dr. Katherine Volk

They don't strongly interact with the planets under the current configuration.

And then here they were looking at this semi-major axis again, but versus this argument of perihelion.

Now every orbit and I'm going to go over this again a little bit later because it's important to the smaller planet suggestion but every object has an orbital plane that it's orbiting the Sun in a plane and that plane is going to intersect our reference plane and the reference plane we use is the orbit of the earth the ecliptic plane and Where it intersects that reference plane we call the ascending node.

So that's where it's coming up through our reference plane and

And the angle between that ascending node and where the object comes to perihelion, its closest approach to the sun, is called this argument of perihelion.

So it's describing where things come to perihelion relative to where they cross the ecliptic plane.

And so Scott Shepard and Chad Trujillo noticed this weird thing where you would expect this angle to be random between minus 180, plus 180, but it didn't appear random in the data.

So they noted this in 2014 and said, maybe there's some monster planet out there that's sculpting these things gravitationally because this is odd and it's not easily explained by observational biases.

And that got some attention, but it really got a lot more attention in 2016 when Mike Brown and Konstantin Badigan at Caltech noticed another thing about these same objects.

These extreme Kuiperveld objects not only shared this argument of perihelion, but their orbits were actually clustered in space.

So this is a top-down view of these extreme objects, and these arrows are showing where the things are at perihelion.

So when in the orbit the object's at perihelion, there's an arrow pointing out.

And as you can see, the arrows are all pointing kind of in one quadrant.

And that's also a little bit odd because you would expect these things to be somewhat randomly distributed if there wasn't something else going on.

So they proposed, they kind of extended this idea of a planet in the outer solar system and said, what could actually cause these orbits to align like that?

And they figured out that if you put a 10 Earth mass planet, 600, 700 AU on average from the sun on an inclined orbit, because these orbits were also kind of aligned in terms of their orbital planes, the net gravitational effect of this extra planet in combination with the known planets in the solar system could cluster these orbits in such a way that it would explain the observations.

So it's a neat story, worked reasonably well.

But of course, it gets more complicated with more data.

There have been discoveries since that initial paper.

And the clustering is starting to look slightly less clustery.