Interaction Cross Sections and Survival Rates for Proposed Solar System Member Planet Nine

Abstract

Motivated by the report of a possible new planetary member of the solar system, this work calculates cross sections for interactions between passing stars and this proposed Planet Nine. Evidence for the new planet is provided by the orbital alignment of Kuiper belt objects, and other solar system properties, which suggest a Neptune-mass object on an eccentric orbit with a semimajor axis a 9 ≈ 400-1500 au. With such a wide orbit, Planet Nine has a large interaction cross section and is susceptible to disruption by passing stars. Using a large ensemble of numerical simulations (several million) and Monte Carlo sampling, we calculate the cross sections for different classes of orbit-altering events: (A) scattering the planet into its proposed orbit from a smaller orbit, (B) ejecting it from the solar system from its current orbit, (C) capturing the planet from another system, and (D) capturing a free-floating planet. Results are presented for a range of orbital elements with planetary mass m 9 = 10 M ⊕ . Removing Planet Nine from the solar system is the most likely outcome. Specifically, we obtain ejection cross sections s int ∼ 5 × 10 6 au 2 (5 × 10 4 au 2 ) for environments corresponding to the birth cluster (field). With these cross sections, Planet Nine is likely to be ejected if the Sun resides within its birth cluster longer than Δt  100 Myr. The probability of ejecting Planet Nine due to passing field stars is 3% over the age of the Sun. Probabilities for producing the inferred Planet Nine orbit are low (5%).

Fly-by encounters between two planetary systems I: Solar system analogues

“…Hence, an encounter closer than ∼1000 au is needed to destabilise such a distant planet. An average star experiences a few such encounters in a few hundred Myr (Malmberg et al 2007;Li & Adams 2016). So the planets scattered or captured onto wide orbits may be vulnerable to external perturbers as long as the star cluster remains compact.…”

New Extreme Trans-Neptunian Objects: Toward a Super-Earth in the Outer Solar System

“…Scattered objects with very distant orbits will likely start to show effects from the distant planet (Lawler et al 2016). Several additional papers have discussed the possible formation, effects and composition of the unseen planet in the distant solar system (Kenyon and Bromley 2016;Fortney et al 2016;Sivaram et al 2016;de la Fuente Marcos and de la Fuente Marcos 2016;Li and Adams 2016;Cowan et al 2016;Beust 2016;Linder and Mordasini 2016;Pauco and Klacka 2016;Mustill et al 2016;Brown and Firth 2016;Whitmire 2016;Gomes et al 2016). …”

Consequences of a Distant Massive Planet on the Large Semimajor Axis Trans-Neptunian Objects

“…These arguments launched a flurry of discussions and studies on the origins, location, and implications of a ninth planet. The studies have covered formation and capture scenarios Cowan et al 2016;Li & Adams 2016;Mustill et al 2016), constraints on the location, detectability and physical properties of P9 de la Fuente Marcos & de la Fuente Marcos 2016aFienga et al 2016;Fortney et al 2016;Ginzburg et al 2016;Holman & Payne 2016aLinder & Mordasini 2016;Philippov & Chobanu 2016;Toth 2016;Veras 2016), the dynamical implications of P9 in the solar system (de la Fuente Marcos et al 2016c;Lawler et al 2016), P9 producing inclined TNOs (Batygin & Brown 2016b), resonances and P9 (Beust 2016;Malhotra et al 2016), a dark matter P9 (Sivaram et al 2016), and impacts of P9 on the Sun's obliquity (Bailey et al 2016;Lai 2016).…”