Is there an exoplanet in the Solar System?

Understand

We investigate the prospects for the capture of the proposed Planet 9 from other stars in the Sun's birth cluster.

• Any capture scenario must satisfy three conditions: the encounter must be more distant than ~150 au to avoid perturbing the Kuiper belt; the other star must have a wide-orbit planet (a>~100au); the planet must be captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit Solar System bodies.
• Here we use N-body simulations to show that these criteria may be simultaneously satisfied.
• In a few percent of slow close encounters in a cluster, bodies are captured onto heliocentric, Planet 9-like orbits.