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|| Sedna | 2012 VP113 ||
On March 26, 2014, astronomers announced the discovery of another dwarf planet in a highly eccentric orbit like Sedna. Designated 2012 VP113, the object comes no closer than 80 AUs to the Sun but ranges out as far as 452 AUs, and so like Sedna, VP113 can be considered to be a member of the "inner Oort Cloud" (which can be defined between 50 and 1,500 AUs from our Sun, Sol, as objects further out will be perturbed into long-period comets by the passing of neighboring stars). Based on its current distance, brightness and presumed albedo (or ability to reflect light), VP113 is likely to be around 280 miles (or 450 kilometers) wide, which would be around half the diameter of Sedna (NASA news release; astronomer Scott S. Sheppard's web page on 2012 VP113; and Trujillo and Sheppard, 2014). VP113 is large enough to have a spherical shape and so is a candidate for IAU designation as a dwarf planet, as defined by the International Astronomical Union (IAU) on August 24, 2006.
As an inner Oort Cloud member not noticeably subject to the gravity of nearby stars or the giant gas and ice planets closer to the Sun, VP113 should have a relatively stable, promordial orbit. VP113, however, is currently located around 83 AUs from our Sun, Sol -- an orbital distance that is close to three times farther out than that of Pluto or Neptune, and it will eventually move more than five times farther away (around 452 AUs) in a 4,590-year orbit around Sol; it's orbital semi-major axis is around 276 AUs with an extremely high eccentricity of 0.710 (more on VP113's orbit from astronomer Scott S. Sheppard.
Because VP113 is located so far from the Sun, its surface temperature never rises above minus 257 degrees Celsius (minus 430 degrees Fahrenheit). Indeed, it is usually even colder as it approaches the Sun only briefly during its 4,600-year Solar orbit. The discovery team presumes that VP113 has an icy reflective surface like other relatively small, outer Solar System objects, as the dwarf planet is observed to have a pink tinge, which is hypothesized to result from chemical changes produced by the effect of radiation on frozen water, methane, and carbon dioxide.
Scott S. Sheppard,
Larger and jumbo illustrations.
Sedna (orange) and VP113 (red)
have extremely large orbits around
the Sun, that appear to lie within
the hypothesized location of the
inner Oort Cloud (more).
Both VP113 and Sedna appear to lie in a transition region between the Edgeworth-Kuiper Belt and the Oort Cloud. Only a few Edgeworth-Kuiper objects (EKOs) such as 2004 XR190 were known to have orbits that stay mostly beyond 50 AUs. Unlike Scattered Disk objects, these EKOs do not move inward within Neptune's gravitational reach but have been named members of the "Extended Scattered Disk," as defined by some astronomers. Two of these objects (1995 TL8 and 2000 YW134) move inward to within to 40 AUs of the Sun but have fairly elliptical orbits that take them back out beyond 60 AUs. According to VP113's discovery team, their and other recent surveys indicate that there are few (although probably not zero) inner Oort cloud objects with perihelion distances (closest orbital point to Sol) between 50 and 75 AUs, which is consistent with stellar encounter models (that include the capture of extrasolar objects) that predict a strong inner edge to the perihelion distribution of outer Solar System objects (Trujillo and Sheppard, 2014).
Extended Scattered Disk objects include 2000 CR105, which moves inward to within 44 AUs of the Sun but then outward beyond 500 AUs, and Sedna, which never comes closer to the Sun than 76 AUs before moving to around 900 AUs away (into the realm of the inner Oort Cloud). Given the large orbital eccentricities of these two objects (which move beyond 500 AUs of the Sun), some astronomers have argued that they were likely to have been strongly perturbed by a massive celestial object (which is unlikely to have been Neptune as they do not come close enough to feel its gravitational influence) such as the passing of a rogue planet (perturbed from its primordial orbit by the gas giants of the inner Solar Sylstem) or one or more passing stars, which could have dragged the two objects farther out after initial orbital perturbation by Neptune or as part of a "first-generation" Oort Cloud. (More discussion on such scenarios from: Emily Lakdawalla, Planetary Society blog, 2014; with illustrations from computer models are available from a 2005 Powerpoint presentation by Brett Gladman and Collin Chan.) Some astronomers have speculated that inner Oort Cloud objects could even be extra-Solar planets gravitationally captured from neighboring stars during the formation of the Solar System.
Scott S. Sheppard,
Under one scenario, a large planet
with around 10 Earth-masses
orbiting at around 250 AUs from
the Sun, could have perturbed both
the orbits of of VP113 and Sedna
within the inner Oort Cloud, (more).
In the case of VP113, it's discovery team has found a strange alignment in its orbit with those of Sedna and 10 other objects that lie closer to the Sun. The orbital angles for these objects cluster in a way which suggests that most of them were perturbed during a single strong gravitational encounter. One explanation for the alignment is the tug of a rocky planet that has as much as 10 Earth-masses and orbits the sun at around 250 AU. While cold and faint, such a planet would be massive enough to push and pull at the closer objects. While NASA's Wide-field Infrared Survey Explorer (WISE) failed to the tell-tale warmth of gas giants like Saturn within 10,000 AUs and larger than Jupiter objects out to 26,000 AUs (NASA/JPL news release), an icy "super-Earth", would have been too cold and faint for WISE to detect -- even if the hypothesized planet has a small internal heat source and absorbs some sunlight.
VP113's discovery team has been using the Dark Energy Camera on the NOAO 4-meter telescope in Chile to conduct their survey. The astronomers have several more candidates for inner Oort Cloud objects which should provide supporting evidence for models of the orbital perturbation of such objects, but it takes about a year of observing to determine whether an orbit is Sedna-like or not. Based on the amount of sky covered so far, they estimate that there may be 900 objects in the inner Oort cloud as big as Sedna, and so the total number of objects in that vast region may well exceed the population of the Main Asteroid Belt or the Edgeworth-Kuiper Belt.
David Seal (a mission planner and engineer at NASA's Jet Propulsion Laboratory at CalTech) has a web site that generates simulated images of the Sun, planets, and major moons from different perspectives and at different times of the year. Try his Solar System Simulator.
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