Predicted Number, Multiplicity, and Orbital Dynamics of TESS M Dwarf Exoplanets

TL;DR

This study predicts that NASA's TESS mission will detect significantly more M dwarf exoplanets and their system architectures than previously expected, revealing high multiplicity and dynamically cooler systems.

Contribution

The paper introduces a new ensemble completeness function and dual-population model to accurately predict TESS's M dwarf exoplanet yield and system architectures.

Findings

TESS will find 990±350 planets around M1V–M4V stars, 1.5 times more than previous estimates.

Approximately 20% of these stars will host two or more transiting planets.

Many transiting planets will be missed due to detection thresholds, but follow-up can uncover additional planets.

Abstract

We present a study of the M dwarf exoplanetary systems forthcoming from NASA's TESS mission. While the mission's footprint is too complex to be characterized by a single detection completeness, we extract an ensemble completeness function that recovers the M dwarf planet detections from previous work. We employ this completeness function, together with a dual-population planet occurrence model that includes compact multiple planetary systems, to infer anew the planet yield. We predict both the number of M dwarf planets likely from TESS and their system architectures. We report four main findings: first, that TESS will likely detect more planets orbiting M dwarfs that previously predicted. Around stars with spectral types between M1V--M4V, we predict TESS will find 990$\pm$350 planets orbiting 715$\pm$255 stars, a 1.5-fold increase over previous predictions. Secondly, TESS will find two or more transiting planets around 20% of these host stars, a number similar to the multiplicity yield of NASA's Kepler mission. Thirdly, TESS light curves in which one or more planets are detected will often contain transits of additional planets below the detection threshold of TESS. Among a typical set of 200 TESS hosts to one or more detected planets, 116$\pm$28 transiting planets will be missed. Transit follow-up efforts with the photometric sensitivity to detect an Earth or larger around a mid-M dwarf, even with very modest period completeness, will readily result in additional planet discoveries. And fourth, the strong preference of TESS for systems of compact multiples indicates that TESS planets will be dynamically cooler on average than Kepler planets, with 90% of TESS-detected planets residing in orbits with $e<0.15$.