by Akshat Rathi, David Rothery and Stephen Lowry, The Conversation
A new, planet-like body has been found on the outer edges of the solar system. This object, called 2012VP113, is the second body of its class found since the identification of the dwarf planet Sedna in 2003. It joins an exclusive club composed of some of the strangest objects in the solar system.
The observable solar system can be divided into three regions: the rocky planets including the Earth and asteroids of the inner solar system, the gas giant planets, and the icy Kuiper Belt objects, which include Pluto. The Kuiper belt stretches from beyond Neptune, which is at 30 astronomical units (one astronomical unit, AU, represents the distance between the Earth and the sun), to about 50AU.
Sedna and 2012VP113 are strange objects, because they reside in a region where there should be nothing, according to our theories of the solar system formation. Their orbit is well beyond that of Neptune, the last recognised planet of the solar system, and even beyond that of Pluto, which differs from planets because of its size, unusual orbit, and composition. (Pluto, once considered a planet, is now considered the lead object of a group of bodies called plutinos.)
The closest Sedna, which is 1000km-wide, gets to the sun is about 76AU and for 2012VP113, which is 450km-wide, that distance is 80AU. Their orbits are also at weird inclinations compared to most other solar system objects.
The results of the discovery have been published in Nature. Chadwick Trujillo of Gemini Observatory in Hawaii, who was also involved in finding Sedna, and Scott Shepherd of the Carnegie Institution for Science, who found 2012VP113 with Trujillo, propose that these objects are members of the inner Oort cloud.
The Oort cloud is a hypothetical region that is thought to stretch outwards beyond the Kuiper belt. Beyond 5000AU, the Oort cloud expands out into a sphere centred on the sun. We have no direct evidence that the Oort cloud exists, but indirect evidence comes in the form of comets with extremely elongated orbits.
Stephen Lowry at the University of Kent said:
“The orbital properties of these two objects are so very different from that of the Kuiper belt objects that it wouldn’t be wrong to suggest they may be part of the inner Oort cloud.”
The fact that these objects exist is remarkable, since they exist in a region where material is thought to have been too sparse for them to form. Current thinking is that they actually formed in the giant-planet region, and that their orbits may carry the signature of whatever events caused them to scatter to such distances. It is hoped that this discovery will lead efforts to find other objects.
David Rothery of Open University said:
“This is a remarkable discovery, but it is not entirely surprising. When they found Sedna, there was hope that they would find others in that region.”
But the fact that it took Trujillo, who was involved in the original team that found Sedna, more than ten years to find Sedna’s neighbour speaks to the challenge of discovery. Lowry said,
“The farther you get from the sun, the less sunlight falls on these objects, which makes the task of locating them harder”.
“Worse still,” Lowry continued -
“the eccentric orbits of these objects means that there is very tiny window in which they can be observed from even the most powerful telescopes on Earth. What is needed to find these objects is not just technology but persistence.”
For example, Sedna gets as close as 76AU away from the sun, but at its farthest it is nearly 1000AU. Its orbital period is about 11,400 years, which means it spends lots of time too far out to be detected.
While 2012VP113 and Sedna provide some information about the inner Oort cloud, to say any more, scientists are going to need more than two data points. Next generation instruments such as the Subaru telescope in Hawaii and Large Synoptic Survey Telescope in Chile may hold the answers.
About the Authors
Akshat has a PhD in organic chemistry from Oxford University as well as a Bachelor of Technology in chemical engineering from the Institute of Chemical Technology in Mumbai. After leaving the lab, he moved into journalism and has written for The Economist, The Hindu and Ars Technica, among others.
David Rothery became Professor of Planetary Geosciences in November 2013, having been a Senior Lecturer in Earth Sciences since 1994. Before that, he was a Lecturer here. He is now in the Department of Physical Sciences, but until 2011 was in the former Department of Earth Sciences. During 1999-2004 Mr. Rothery was Director of Teaching and Geosciences Programme Director. I had also been Leader of the IAVCEI Commission on Remote Sensing, and in 2005, he was appointed to the PPARC Solar System Advisory Panel and the BepiColombo Oversight Committee. In May 2006, he was appointed UK Lead Scientist on MIXS (Mercury Imaging X-ray Spectrometer), which is the only UK Principal Investigator instrument on BepiColombo, the European Space Agency mission to Mercury to be launched in 2014. Mr. Rothery chairs ESA's Mercury Surface and Composition Working Group. He was also a member of the Science Advisory Panel for C1XS , the X-ray spectrometer on Chandrayaan-1 (launched 22 Oct 2008). In 2006-7, he served on the ESSC/ESF Ad Hoc Group on Definition of a science-driven European scenario for space exploration. His research interests centre on the study of volcanic activity by means of remote sensing, and volcanology and geoscience in general on other planets.
Dr. Lowry is a Senior Lecturer at the University of Kent's Centre for Astrophysics and Planetary Science. He specializes in optical and infrared observations and modeling of Solar System Small Bodies, making use of both space-based and large ground-based telescope facilities. He completed his PhD in 2001 at Queen's University Belfast in the area of cometary science, and from there he was a research fellow for several years in the UK and US. Before moving to his current position at the University of Kent, he was a Research Scientist at NASA's Jet Propulsion Laboratory working on physical and compositional characterizations of cometary and asteroidal bodies, and supported numerous spacecraft missions to these bodies and the development of a new comet surface sample return mission. His publications include four research papers in Science and one in the Nature, and was lead author in a chapter in the recent 'The Solar System Beyond Neptune' book. Dr. Lowry is a member of the science team for the OSIRIS optical camera instrument on board ESA's Rosetta spacecraft, en route to comet 67P/Churyumov-Gerasimenko, and is Principal Investigator on a new Large Programme at the European Southern Observatory to study near-Earth asteroids.