A New Dwarf Planet, and Maybe Something More

A discovery at the solar system’s edge revives the possibility of a mysterious Planet X.

2012 VP 113.jpg
Say hello to my little friend: 2012 VP 113 is caught moving against a background of stars in three images (red, green, blue), each taken two hours apart.

The discovery of a new dwarf planet at the far edge of the solar system is interesting, I suppose. About as wide as the state of Missouri, 2012 VP 113 (temporarily nicknamed “Biden” for the VP in the official designation) is the second large object found in the so-called inner Oort cloud beyond Pluto. Astronomers Chad Trujillo and Scott Sheppard, who made the discovery, suspect that hundreds more of these objects await detection.

What really intrigues me, though, is what they didn’t find, but still suspect—a much larger planet, maybe ten times the size of Earth, that influences the orbits of Biden and a nearby mini-world called Sedna. Trujillo and Sheppard noticed that one of the orbital elements, the argument of perihelion, is similar for both objects. One possible explanation is a super-Earth out in the distant solar system that perturbs the orbits of the smaller bodies.

Astronomers have long theorized another “Planet X” beyond Neptune and Pluto, but just recently, a search with NASA’s WISE infrared space telescope came up empty. Or at least it found nothing as big as Saturn (100 times the size of Earth) out to a distance of 10,000 astronomical units (the distance between Earth and the Sun).

Trujillo and Sheppard suggest, rather tentatively, that there might be a smaller planet that’s closer in (something like 250 AU), however. And WISE isn’t sensitive enough to see that, says Kevin Luhman of Penn State University, who did the study. Fortunately, new telescopes are on the way that may be able to find such a super-Earth if it exists: the Pan-STARRS telescopes in Hawaii and the Large Synoptic Survey Telescope (LSST), which is due to come online around 2021.