Orbit diagram for the outer solar system. Jupiter, Saturn, Uranus and Neptune are shown by solid purple lines, while the Kuiper belt is depicted by the dotted blue region. Sedna's orbit is orange, and VP113 is red.
(Credit: Scott Sheppard)
A dwarf planet out beyond Pluto has been found orbiting our sun — and there may be another planet 10 times the size of Earth.
Our solar system is now officially just a little bit bigger. Out beyond the known edges of our solar system, Carnegie Institution for Science's Scott Sheppard and Gemini Obervatory's Chadwick Trujillo have discovered a dwarf planet orbiting the sun. Named 2012 VP113, it is thought to be just one of thousands of objects that are thought to make up the inner Oort cloud.
Although VP113 is just 450 kilometres across, Sheppard and Trujillo have also found evidence that there may be a much bigger planet out there. They have extrapolated its presence based on a gravitational effect on VP113's orbit, as well as other objects in the Oort cloud.
The solar system had previously been defined by the Kuiper belt, a field of icy debris — including Pluto — that extends out beyond Neptune. Until the discovery of VP113, there was only thought to be one object past the Kuiper belt — the 995-kilometre diameter planetoid Sedna, discovered in 2003.
"This is an extraordinary result that redefines our understanding of our Solar System," says Linda Elkins-Tanton, director of Carnegie's Department of Terrestrial Magnetism.
VP113 was spotted using the new 570-megapixel(DECam) in Chile. It has the largest field-of-view of any large telescope, meaning it can detect faint objects unseen by other telescopes. The planetoid's orbit and surface properties were then determined using the Magellan 6.5-meter telescope at Carnegie's Las Campanas Observatory.
VP113 has a pinkish hue due to radiation damage that alters the composition of the ice, methane and carbon dioxide that make up the planet. It also has the greatest known distance of any object orbiting the sun — 12 billion kilometres at its closest point (the perihelion), about 80 times the distance of the Earth, or 80AU (astronomical units). The Kuiper belt is between 30 and 50AU, and Sedna orbits at 76AU. At its farthest point (the aphelion), VP113 hits 446AU.
Yet it is only one of what Sheppard and Trujillo think could be around 900 objects with similar orbits and sizes larger than 1000 kilometres.
"The search for these distant inner Oort cloud objects beyond Sedna and 2012 VP113 should continue, as they could tell us a lot about how our Solar System formed and evolved," Sheppard said. "Some of these inner Oort cloud objects could rival the size of Mars or even Earth. This is because many of the inner Oort cloud objects are so distant that even very large ones would be too faint to detect with current technology."
One of these objects could be what is known as a super-Earth — a planet larger than the Earth but smaller than Uranus. The orbits of both Sedna and VP113 — as well as a few other objects near the edge of the Kuiper belt — suggest that a massive body is shepherding these objects into similar orbital configurations.
The results of the research have been published online in the journal Nature.