March 28, 2014
More than 10 years after Sedna was discovered, another dwarf planet - 2012 VP113 - was found at outer reaches of the solar system.
Orbits of 2012 VP113 (red) and Sedna (orange) around Kuiper belt (blue). Credit: Scott S. Sheppard/Carnegie Institution for Science
In 2003, astronomers discovered a small planet that was then labeled as the tenth planet in the solar system, but eventually, it was classified as a dwarf planet named Sedna, together with Pluto. Sedna has highly elliptical orbit around the Sun. The closest it gets to our star is 76 astronomical units (AU), the farthest is about 1,000 astronomical units. One AU is Earth's distance to Sun, almost 150 million kilometres. Now, we have another dwarf planet with similar orbit.
Newly discovered dwarf planet, named 2012 VP113 for now, gets to 80 astronomical units close to the Sun, but its farthest distance is about 450 astronomical units. It is probably made of ice and about 450 kilometres across.
The origin of 2012 VP113 as well as Sedna is a mystery for now. Many computer models don't give up on long-theorised Planet X – the tenth planet suggested to exist somewhere on the edge of the solar system.
Orbits of 2012 VP113 and similar objects suggest they were pulled away from inner parts of the solar system by a neighbouring star or another, larger planet. It could have been rougue planet just passing through the solar system. It also could have been a planet couple of times more massive than Earth, formed closer to the Sun and then ejected in the midst of a chaos during the formation of the system. This ejected planet could still be orbitin the Sun at great distances, at the inner edge of the theorised Oort cloud
Beyond Neptune's orbit, there's a large number of icy objects that make the Kuiper belt. As its name suggests, it looks like a belt or a ring around the Sun and its eight planets. It starts at 30 astronomical units and ends after 50 astronomical units. Pluto is one of the objects in this belt. Beyond that, there is a theorised Oort cloud – a spherical cloud of icy objects anywhere from 10.000 to 50,000 astronomical units from the Sun.
Some models suggest there was one or more Earth-like planets that formed in the region where we today have four gas giants. If one of those planets ended up near at the inner edge of the Oort cloud bringing smaller planets with it, it is not known.
"What happened to those objects – if they collided with the giant planets and eventually became a part of the giant planets, or if they got ejected – is not known," said Scott Sheppard of the Carnegie Institution of Washington DC, USA. He is the co-discoverer of 2012 VP113. "The bigger the object, the more planets it could pull out to this region."
"It's like looking out your car window while you're driving on the highway," says Sheppard's colleague Chad Trujillo at Gemini Observatory in Hilo, Hawaii, USA, explaining why it takes so long to detect these objects. "Things that are very close move very quickly with respect to the background things and things that are more distant, like mountains, move slowly. The technique is to basically to look for objects that move with respect to the background stars, but move very slowly. The slower they move, the farther away they are."
Trujillo and Sheppard are working on confirmation of additional six candidates in the same region, but they suspect there could be hundreds more in the inner Oort cloud.