The Case for an Early Solar Binary Companion

TL;DR

This paper proposes that the early Sun had a temporary binary companion, which increased the likelihood of forming the outer Oort cloud and capturing Planet Nine, with testable predictions for future observations.

Contribution

It introduces a binary companion model for the Sun's early history, explaining the origin of Planet Nine and the outer Oort cloud more effectively than single-star models.

Findings

Binary companion increases likelihood of outer Oort cloud formation.

Capture of Planet Nine is more probable in the binary model.

Predicts overabundance of dwarf planets with similar orbits to Planet Nine.

Abstract

We show that an equal-mass, temporary binary companion to the Sun in the solar birth cluster at a separation of $\sim 10^3 \; \mathrm{\; AU}$ would have increased the likelihood of forming the observed population of outer Oort cloud objects and of capturing Planet Nine. In particular, the discovery of a captured origin for Planet Nine would favor our binary model by an order of magnitude relative to a lone stellar history. Our model predicts an overabundance of dwarf planets, discoverable by LSST, with similar orbits to Planet Nine, which would result from capture by the stellar binary.