Are There Unseen Planets Lurking in the Kuiper Belt? by Kathryn Volk - November 1, 2017
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Tonight's lecture is going to be by Dr. Katherine Volk. Kat got her bachelor's at Wittenberg in Ohio, then came here and got a PhD, went and did a postdoctoral fellowship at the University of British Columbia in Vancouver, and then came back to Tucson where she's been for the last two or three years. Yeah, something like that. Something like that. And so she'll be talking tonight about whether there are, as she puts it, unseen planets lurking in the Kuiper Belt. And this has been a topic that's been a really interesting one. The biggest national meeting of planetary scientists last week, there were all sorts of arguments about whether there are planets out there, how many there might be, all that sort of thing.
Heated arguments. Heated arguments, yes. So without further ado, Katherine Wolk.
All right, thanks, Tim. All right, so as Tim said, how's the volume by the way, is that okay? All right, so I'm gonna be talking about unseen planets potentially in the Kuiper Belt. So here's the roadmap for the talk that we're gonna quickly review, make sure everybody's familiar with the Kuiper Belt, talk a little bit about how we actually detect things out there because it's an important part of the story. And then talk about how complete or incomplete our inventory is for the solar system, and really set the stage for why we've been talking so much lately about whether there are unseen planets out there yet to be discovered. So first, quick tour. So our solar system has two kind of what we call debris disks or belts of small bodies.
These are leftover things that didn't get made into larger planets. In the inner solar system between Mars and Jupiter, we have the asteroid belt. And then out past Neptune's orbit, we have the Kuiper Belt in the outer solar system. So I'm just going to give a quick top-down view here of the Kuiper Belt. So everything in white here is an observed Kuiper Belt object. And we have Neptune, Uranus, Saturn, and Jupiter. And then the sun and all the terrestrial planets would be tiny circles just mucking up the plot, so I didn't put them in. And if we look on a kind of a side-on view, we see that there's some vertical structure here, which is going to play a role later on in the talk. But we can see there's quite a few dots out here, but not nearly as many as we have for the asteroid belt.
And in the Kuiper belt, we have a couple different kinds of orbits. Now we have what we call the so-called classical belts. This is, again, a top-down view of the solar system, where the red circles here are things on low eccentricity, low inclination orbits that are kind of between 40 and 45 AU from the sun. One AU, of course, is the Earth-sun distance. Neptune's at 30. We call those the classical Kuiper belt because that's kind of what was envisioned when the Kuiper belt was first proposed. But then of course there are higher eccentricity, scattering, and then there's a few other categories of scattering or extreme or detached Kuiper belt objects. If we just take out the classical ones for a moment.
The scattering things get out to very large distances from the Sun, but their close approach is still kind of in Neptune's neighborhood, where they can still have strong gravitational interactions, which is part of how they got scattered out. So that's kind of broadly speaking the two types of orbits we have out in the Kuiper Belt. And if we now make this sort of plot for all of the known KBOs as of a few months ago, we can see this bundle of these circular, roughly circular classical belt, and then all of these scattering and even some really extremely distant Kuiper belt objects that we will come back to later. So that's just the really brief overview of the Kuiper belt to give you some orientation.
But now I want to talk about how did we actually discover all of these things out in the Kuiper Belt? How do we know they're there and what kind of orbits they're on? So when we're looking for new solar system objects, what we're doing is we're scanning the night sky for anything that's moving against the background stars.
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