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Our solar system has a new ninth planet! Sorry, it's not Pluto, but if it helps, the same guy who got Pluto demoted was also part of the team that found Planet Nine. Oh, and, no one has actually seen it. Yet. Caltech researchers, Drs. Konstantin Batygin and Mike Brown, recently described the creatively nicknamed Planet Nine in the Astronomical Journal. To learn more about it, I spoke with Dr. Dan Caton, professor of astronomy at Appalachian State University.

Dr. Daniel Caton interviewing for SciWorks Radio at the Appalachian State University Podcast Studio. Credit : Shawn Fitzmaurice
This was discovered by looking at a handful of these objects in the so-called Kuiper belt. They do have very elliptical orbits, and they seem to all be aligned in the same quadrant of the orbital plane that's dominated by the planets in the solar system. They all have their closest approach to the sun angle - an angle we call the argument of the perihelion (which is a funny sounding name) -  they're all in about the same plane of orbit, and the chances of that happening randomly is exceedingly small; less than one in 10,000. So there is a statistical argument that there's some perturber that keeps them aligned in this common orientation.

But no one has seen Planet Nine, so, without direct observation, the scientists put the evidence through mathematical modeling.

They ran simulations where they started with six test particles, as we call them, in an in-body orbit calculation, and saw what they did. That's the only way to really do it. You can calculate the orbit of two bodies around each other; like the earth-moon, earth-sun, and so-forth, exactly with analytical equations. If you add a third similar body there's no solution. And so you have to do it with simple physics where you set up the main players, and you let things move and you move it incrementally. At little steps, at each step you calculate the forces because the distances are all changing, and then you step it again, and so-forth. And they did a lot of runs on this and verified the theory that way.

Given only evidence, we've learned quite a bit about the still theoretical Planet Nine.

We know about what its orbit is like, but we don't know where it is in that ellipse. Wherever he is in his orbit, his orbit is so large that he hasn't achieved a whole orbit since the last ice age.

Planet Nine's orbit ranges from 5 to 25 times more distant from the sun than Pluto. Think about that. At those distances, sunlight ranges from 1 to 6 days' travel before hitting the planet's surface. Using math, we also know this distant object's mass.

Maybe 10 times the size of the earth. Uranus and Neptune are in the 15 earth mass range. So, it's up in that ballpark. That's about all we know.

Mass is a measure of how much of something there is, but not of physical size. It could be rocky and dense like our earth, making it a relatively small rock ball, or light and fluffy, like Saturn, making it much larger. That won't be known until it is actually observed. When and if it is found, score one for the predictive power of science!

To expand this and project it forward and I think we're in the era of really figuring out what our solar system is like. Particularly when the LSST, comes on line. That's the Large Synoptic Survey Telescope. And this guy is going to be a big telescope in Chile. It is going to scan the skies continuously for several years. So there's going to be massive amounts of data. I mean, this is big data in the world of science. But that's predicted to turn up probably thousands of Kuiper Belt objects. And since it's observing regularly, you'll get orbit determinations.

This Time Round, the theme music for SciWorks Radio, appears as a generous contribution by the band Storyman and courtesy of

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