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The known Solar System can be divided into three parts: the rocky planets like Earth, which are close to the Sun; the gas giant planets, which are further out; and the frozen objects of the Kuiper belt, which lie just beyond Neptune's orbit. Beyond this, there appears to be an edge to the Solar System where only one object, Sedna, was known to exist. New work from Scott S. Sheppard (Carnegie Institution for Science) and Chad Trujillo (Gemini Observatory) report the discovery of a second object, dwarf planet 2012 VP113, found beyond this edge. The new discovery opens up the fourth domain of the solar system and suggests a massive unknown planet orbits in this region. This work is now published in the March 27, 2014 issue of the journal Nature. 2012 VP113 is the provisional designation of the object, which the discovers affectionately are calling "Biden" because of the VP in the objects name.
Figure 1: The discovery images of 2012 VP113 (affectionately nicknamed "Biden" because of the VP in the provisional name). It has the most distant orbit known in our Solar System as it never comes closer than 80 AU to the Sun, which is about 2.5 times more distant than Pluto's current position. Three images of the night sky from the Dark Energy Camera at CTIO in Chile, each taken about 2 hours apart, were combined into one. The first image was artificially colored red, second green and third blue. 2012 VP113 moved between each image as seen by the red, green and blue dots. The background stars and galaxies did not move and thus their red, green and blue images combine to show up as white sources.
Credit: Scott S. Sheppard/Carnegie Institution for Science
Credit: Scott S. Sheppard/Carnegie Institution for Science
In 2003, the dwarf planet Sedna was discovered beyond the Kuiper Belt edge and it was not known if Sedna was unique, like Pluto once was thought to be before the Kuiper Belt was discovered. "With the discovery of 2012 VP113 it is now clear Sedna is not unique and is likely the second known member of the hypothesized inner Oort cloud, from where some of the comets may originate", says Trujillo.
2012 VP113's closest orbit point to the Sun brings it to about 80 times the distance that the Earth is from the Sun, a measurement referred to as an astronomical unit or AU. For context, the rocky planets and asteroids exist at distances ranging between .39 and 4.2 AU. Gas giants are found between 5 and 30 AU, and the Kuiper belt (composed of thousands of icy objects, including Pluto) ranges from 30 to 50 AU. In our solar system there is a distinct edge at 50 AU, of which only Sedna was known to stay significantly beyond at 76 AU for its entire orbit. "The search for more of these distant inner Oort cloud objects should continue, as they can tell us a lot about how our solar system formed and evolved", says Sheppard.
Surprisingly, the similarity in the orbits found for Sedna, 2012 VP113 and a few other extreme objects near the edge of the Kuiper Belt suggests that an unknown massive planet may be gravitationally shepherding these objects into these similar orbital configurations. Sheppard and Trujillo show a Super Earth (2-15 Earth masses) from about 200 AU with a possible inclined orbit at some 1500 AU could create the shepherding effect seen in the orbits of these objects, which are too distant to be perturbed significantly by any of the known planets. This is the first strong evidence that a massive planet beyond Neptune does exist, which would be some ten times the distance of Neptune and well beyond the fabled Planet X, so it would be more like Planet Y.
Sheppard and Trujillo used the new Dark Energy Camera (DECam) on the NOAO 4 meter telescope in Chile for discovery. DECam has the largest field-of-view of any 4 meter or larger telescope, giving it unprecedented ability to search large areas of sky for faint objects. The Magellan 6.5 meter telescope was used to determine the orbit of 2012 VP113 and obtain detailed information about its surface properties.
From the amount of sky area searched, Sheppard and Trujillo determine that about 900 objects with orbits like Sedna and 2012 VP113 are out there with sizes larger than 1000 km and that the total population of the inner Oort cloud is likely bigger than the Kuiper Belt and main asteroid belt.
Orbit diagram for the outer solar system. The Sun and Terrestrial planets are at the center. The orbits of the four giant planet Jupiter, Saturn, Uranus and Neptune are shown by purple solid circles. The Kuiper Belt (including Pluto) is shown by the dotted light blue region just beyond the giant planets. Sedna's orbit is shown in orange while 2012 VP113's orbit is shown in red. Both objects are currently near their closest approach to the Sun (perihelion). They would be too faint to detect when in the outer parts of their orbits. Notice that both orbits have similar perihelion locations on the sky and both are far away from the giant planet and Kuiper Belt regions
Plot of all the known bodies in the outer solar system with their closest approach to the Sun (Perihelion) and eccentricity. 2012 VP113 has the most distant closest approach to the Sun of any known solar system object.
There are three competing theories for how the inner Oort cloud might have formed. As more objects are found, it will be easier to narrow down which of these theories is most likely accurate. One theory is that a rogue planet could have been tossed out of the giant planet region and this planet could have perturbed objects out of the Kuiper Belt to the inner Oort cloud on its way out. This planet could have been ejected or still be in the distant solar system today. The second theory is that a close stellar encounter could put objects into the inner Oort cloud region while a third theory suggests inner Oort cloud objects are captured extra-solar planets from other stars that were near our Sun in its birth cluster.
The outer Oort cloud is distinguished from the inner Oort cloud because in the Outer Oort cloud, starting around 1500 AU, the gravity from other nearby stars starts to perturb the orbits of the objects, causing objects in the outer Oort cloud to have their orbits change drastically over time. This creates many of the comets we see as objects that were perturbed out of the Outer Oort Cloud. Inner Oort cloud objects are not highly affected by the gravity of other stars and thus have more stable and thus primordial orbits.
The three discovery images of 2012 VP113 combined into a movie to show the motion of this distant solar system object compared to the background stars and galaxies. The images were taken about 2 hours apart on UT November 5, 2012 with the Dark Energy Camera (DECam) on the CTIO 4 meter telescope in Chile operated by the NSF of the United States. The motion of 2012 VP113 clearly stands out compared to the steady state background of stars and galaxies.
Credit: Scott S. Sheppard/Carnegie Institution for Science
Credit: Scott S. Sheppard/Carnegie Institution for Science
This work was partially funded by NASA.
This project used data obtained with DECam, which was constructed bythe Dark Energy Survey collaborating institutions.
Observations were partly obtained at Cerro Tololo Inter-AmericanObservatory, National Optical Astronomy Observatory, operated by theFoundation of Universities for Research in Astronomy, under contractwith the National Science Foundation.
This paper includes data gathered with the Carnegie 6.5 meter MagellanTelescopes located at Las Campanas Observatory, Chile.
This project used data obtained with DECam, which was constructed bythe Dark Energy Survey collaborating institutions.
Observations were partly obtained at Cerro Tololo Inter-AmericanObservatory, National Optical Astronomy Observatory, operated by theFoundation of Universities for Research in Astronomy, under contractwith the National Science Foundation.
This paper includes data gathered with the Carnegie 6.5 meter MagellanTelescopes located at Las Campanas Observatory, Chile.
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