CONSTRAINTS ON THE LOCATION OF A POSSIBLE 9TH PLANET

Image: The six most distant known objects in the solar system with orbits exclusively beyond Neptune (magenta) all mysteriously line up in a single direction. Such an orbital alignment can only be maintained by some outside force, Batygin and Brown say. Their paper argues that a planet with 10 times the mass of the earth in a distant eccentric orbit anti-aligned with the other six objects (orange) is required to maintain this configuration. Credit: Caltech

The astronomers have noticed some of the dwarf planets and other small, icy objects tend to follow orbits that cluster together. To explain the unusual distribution of these Kuiper Belt objects, several authors have advocated the existence of a superEarth planet in the outer solar system (planet Nine or planet X).


The prediction is based on detailed mathematical modeling and computer simulations, not direct observation. It has recently been proposed that a 10 M_earth object with an orbit of 700 AU semi major axis and 0.6 eccentricity can explain the observed distribution of Kuiper Belt objects around Sedna, a large minor planet in the outer reaches of the Solar System that was, as of 2015, at a distance of about 86 astronomical units (AU) from the Sun, about three times as far as Neptune.

Figure 1: Allowed zone for P9. The red zone (C14) is excluded by the analysis of the Cassini data up to 2014. The pink zone (C20) is how much this zone can be enlarged by extending the Cassini data to 2020. The green zone is the most probable zone for P9 (v ∈ [108◦:129◦]), with maximum reduction of the residuals at v = 117.8 ◦ (blue dot P9). The white zone is the uncertainty zone where the P9 perturbation is too faint to be detected. Credit: (Fienga et al. 2016)

In a recent paper (Fienga et al 2016) the authors try to obtain informations about the position of the planet X analyzing the Saturn orbit data obtained thanks to the tracking of the Cassini spacecraft during its exploration of the Saturnian system. According to their analysis the allowed zone for the actual position of the planet X are those shown in Figure 1.

• Fienga et al. 2016 - Constraints on the location of a possible 9th planet derived from the Cassini data (arXiv)
• Planet X - (NASA) (Wikipedia)