Planet Nine
Artist's impression of Planet Nine as an ice giant eclipsing the central Milky Way, with the Sun in the distance. Neptune's orbit is shown as a small ellipse around the Sun. (See labeled version.)
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|
| Orbital characteristics | |
|---|---|
| Aphelion | 1,200 AU (est.) |
| Perihelion | 200 AU (est.) |
| 700 AU (est.) | |
| Eccentricity | 0.6 (est.) |
| 10,000 to 20,000 years | |
| Inclination | 30° to ecliptic (est.) |
| 150° (est.) | |
| Physical characteristics | |
|
Mean radius
|
13,000 to 26,000 km (8,000–16,000 mi) 2–4 R⊕ (est.) |
| Mass |
6×1025 kg (est.) ≥10 M⊕ (est.) |
| >22.5 (est.) | |
Planet Nine is a hypothetical large planet in the far outer Solar System, the gravitational effects of which would explain the improbable orbital configuration of a group of trans-Neptunian objects (TNOs) that orbit mostly beyond the Kuiper belt.
In a 2014 letter to the journal Nature, astronomers Chad Trujillo and Scott S. Sheppard inferred the possible existence of a massive trans-Neptunian planet from similarities in the orbits of the distant trans-Neptunian objects Sedna and 2012 VP113. On 20 January 2016, researchers Konstantin Batygin and Michael E. Brown at Caltech explained how a massive outer planet would be the likeliest explanation for the similarities in orbits of six distant objects, and they proposed specific orbital parameters. The predicted planet could be a super-Earth, with an estimated mass of 10 Earths (approximately 5,000 times the mass of Pluto), a diameter two to four times that of Earth, and a highly elliptical orbit with an orbital period of approximately 15,000 years.
On the basis of models of planet formation that might include planetary migration from the inner Solar System, such as the five-planet Nice model, Batygin and Brown suggest that it may be a primordial giant planet core that was ejected from its original orbit during the nebular epoch of the Solar System's evolution. Others have proposed that it was captured from another star, or that it formed on a very distant circular orbit and was perturbed onto its current eccentric orbit during a distant encounter with another star.
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