The Demographics of Wide-Separation Planets

TL;DR

This review discusses the current understanding, detection methods, and challenges in characterizing the demographics of wide-separation exoplanets beyond the snow line, emphasizing future prospects for comprehensive statistical surveys.

Contribution

It provides an overview of detection techniques, their sensitivities to wide-separation planets, and discusses the challenges and future directions in exoplanet demographic studies beyond the snow line.

Findings

Detection methods vary in sensitivity to wide-separation planets.

Scaling relations help estimate detectability based on physical parameters.

Future surveys aim for a nearly complete statistical census.

Abstract

I begin this review by first defining what is meant by exoplanet demographics, and then motivating why we would like as broad a picture of exoplanet demographics as possible. I then outline the methodology and pitfalls to measuring exoplanet demographics in practice. I next review the methods of detecting exoplanets, focusing on the ability of these methods to detect wide separation planets. For the purposes of this review, I define wide separation as separations beyond the 'snow line' of the protoplanetary disk, which is at roughly $\sim3$ au for a sunlike star. I note that this definition is somewhat arbitrary, and the practical boundary depends on the host star mass, planet mass and radius, and detection method. I review the approximate scaling relations for the signal-to-noise ratio for the detectability of exoplanets as a function of the relevant physical parameters, including the host star properties. I provide abroad overview of what has already been learned from the transit, radial velocity, direct imaging, and microlensing methods. I outline the challenges to synthesizing the demographics using different methods and discuss some preliminary first steps in this direction. Finally, I describe future prospects for providing a nearly complete statistical census of exoplanets.