Detecting Exomoons Via Doppler Monitoring of Directly Imaged Exoplanets

TL;DR

This paper explores the potential to detect large exomoons around directly imaged exoplanets using Doppler spectroscopy, suggesting feasible detection with current or upcoming instruments and additional insights into planetary spin orientations.

Contribution

It introduces a novel method for detecting massive exomoons via Doppler shifts in directly imaged exoplanets and discusses its implications for planetary system characterization.

Findings

A Neptune-sized exomoon would induce a 200 m/s radial velocity signal.

Current and next-generation instruments could detect such exomoons.

Radial velocity surveys can also reveal planetary spin axis orientations.

Abstract

Recently, Teachey, Kipping, and Schmitt (2018) reported the detection of a candidate exomoon, tentatively designated Kepler-1625b I, around a giant planet in the Kepler field. The candidate exomoon would be about the size and mass of Neptune, considerably larger than any moon in our Solar System, and if confirmed, would be the first in a new class of giant moons or binary planets. Motivated by the large mass ratio in the Kepler-1625b planet and satellite system, we investigate the detectability of similarly massive exomoons around directly imaged exoplanets via Doppler spectroscopy. The candidate moon around Kepler-1625b would induce a radial velocity signal of about 200 m/s on its host planet, large enough that similar moons around directly imaged planets orbiting bright, nearby stars might be detected with current or next generation instrumentation. In addition to searching for exomoons, a radial velocity survey of directly imaged planets could reveal the orientations of the planets' spin axes, making it possible to identify Uranus analogs.