Misaligned Protoplanetary Disks in a Young Binary System

TL;DR

This study reveals that the protoplanetary disks in the young binary system HK Tau are significantly misaligned, providing evidence that such misalignments can influence planetary orbit evolution during formation.

Contribution

First direct measurement of the three-dimensional misalignment of the bulk of the planet-forming disks in a young binary system, supporting theories of misalignment-driven orbital evolution.

Findings

Disks in HK Tau are misaligned by 60-68 degrees.

Misalignments are present at the time of planet formation.

Conditions for misalignment-driven mechanisms exist early in binary systems.

Abstract

Many extrasolar planets follow orbits that differ from the nearly coplanar and circular orbits found in our solar system; orbits may be eccentric or inclined with respect to the host star's equator, and the population of giant planets orbiting close to their host stars suggests significant orbital migration. There is currently no consensus on what produces such orbits. Theoretical explanations often invoke interactions with a binary companion star on an orbit that is inclined relative to the planet's orbital plane. Such mechanisms require significant mutual inclinations between planetary and binary star orbital planes. The protoplanetary disks in a few young binaries are misaligned, but these measurements are sensitive only to a small portion of the inner disk, and the three-dimensional misalignment of the bulk of the planet-forming disk mass has hitherto not been determined. Here we report that the protoplanetary disks in the young binary system HK Tau are misaligned by 60{\deg}-68{\deg}, so one or both disks are significantly inclined to the binary orbital plane. Our results demonstrate that the necessary conditions exist for misalignment-driven mechanisms to modify planetary orbits, and that these conditions are present at the time of planet formation, apparently due to the binary formation process.