Two astronomers argue that the farthest objects in the Kuiper Belt are being pushed and pulled by the gravity of Planet Nine, a giant planet orbiting over 10 times farther from the Sun than Neptune. If they find it, it’ll be the first real expansion of the Sun’s planetary album in 170 years.
The Evidence for Planet Nine’s Existence
Published: June 10, 2019
Onscreen: There’s a massive planet on the edge of our solar system — at least that’s what some astronomers think. But why?
The Evidence for Planet 9. Funded in part by Draper.
Mike Brown: Everything that Planet 9 does to our solar system is done by gravity. So it's the gravitational influence of Planet 9 that we are basically reading.
Onscreen: Konstantin Batygin and Mike Brown study the Kuiper Belt — the rocky region beyond Neptune. They think that the furthest out objects in the Kuiper Belt are being pushed and pulled by the gravity of Planet 9.
Konstantin Batygin: Here what we see here in purple, these are the huge orbits of the distant Kuiper Belt Objects. They all kind of lie in the same plane. They’re all arranged into the same overall direction. So, something is gravitationally shepherding them. This object is Planet 9.
Onscreen: Planet 9, a giant planet over five times the mass of Earth and orbiting over ten times farther than Neptune.
Brown: Standing up and saying, “We think there's a ninth planet” is a pretty dramatic thing to say and if we were going to say that, we didn't want to be wrong. In fact, since the time even of Percival Lowell, and even earlier, people have been talking about new planets, and new planets, and new planets. And they're always wrong. For 150 years if you stood up and said I think there's a new planet, you were wrong.
Onscreen: But the more they looked at the structure of the solar system, the more evidence they saw.
Brown: Planet 9, in the most sort of surprising thing: It tilts the entire solar system by about 6 degrees with respect to the sun. Planet 9 could very naturally explain that.
Onscreen: And that’s not all.
Batygin: Yet another population of distant bodies that Planet 9 predicts is objects called Centaurs that orbit out of the plane of the solar system. They’re perpendicular to the planetary orbits.
Onscreen: These predicted objects have now been discovered.
Batygin: The fact that these objects have been observed, and they really are there, is one of the strongest lines of evidence we have towards the true existence of Planet 9 itself.
Brown: There's now a laundry list of things that Planet 9 does that we see. It is it is inconceivable to me that there is not a Planet 9 out there. There are just too many things that were previously unexplained that Planet 9 naturally explains.
Onscreen: If they find Planet 9, it’ll be a game changer.
Batygin: The astronomical confirmation of the existence of Planet 9 will be the first real expansion of the Sun's planetary album in 170 years. It would completely redefine our scale of what the solar system really looks like.
Onscreen: Now, astronomers around the world are searching the skies to see if they can actually spot this 9th planet.
Next: Hunting for Planet 9.
Produced and Directed by: Caitlin Saks and Terri Randall
Camera: Dave Arabia
Digital Producer: Ana Aceves
Additional Footage: Adler Planetarium, Joe Tucciarone, ESO/A. Santerne, Ed Bell Media, National Astronomical Observatory of Japan, Mike Brown, Konstantin Batygin
© WGBH Educational Foundation 2019