Solar Obliquity Induced by Planet Nine
The six-degree obliquity of the Sun suggests that either an asymmetry was present in the solar system's formation environment, or an external torque has misaligned the angular momentum vectors of the Sun and the planets. However, the exact origin of this obliquity remains an open question. Batygin & Brown have recently shown that the physical alignment of distant Kuiper Belt orbits can be explained by a 5-20 m_⊕ planet on a distant, eccentric, and inclined orbit, with an approximate perihelion distance of ~250 au. Using an analytic model for secular interactions between Planet Nine and the remaining giant planets, here, we show that a planet with similar parameters can naturally generate the observed obliquity as well as the specific pole position of the Sun's spin axis, from a nearly aligned initial state. Thus, Planet Nine offers a testable explanation for the otherwise mysterious spin–orbit misalignment of the solar system.
© 2016. The American Astronomical Society. Received 2016 June 24; revised 2016 August 12; accepted 2016 August 23; published 2016 October 21. We are grateful to Chris Spalding and Roger Fu for useful discussions, and to the anonymous reviewer for insightful comments.
Published - Bailey_2016_AJ_152_126.pdf
Submitted - 1607.03963.pdf