The JWST Search for Earth-Luna Analogs: Upper Limits on Exomoons and Refined Ephemerides for TOI 700 d and e

TL;DR

This study used JWST to search for Earth-Luna analog exomoons around TOI 700 d and e, refining planetary data and identifying noise sources that limit moon detection sensitivity.

Contribution

The paper presents the first JWST search for exomoons around habitable-zone M-dwarf planets and improves ephemerides while analyzing noise impacts on detection capabilities.

Findings

Refined planetary ephemerides with an order-of-magnitude period accuracy improvement.

Identified stellar granulation noise affecting JWST transit observations.

Sensitivity limited to moons larger than Ganymede due to noise, but future corrections could enable Luna-analog detection.

Abstract

While no conclusive detections of exomoons have been reported to date, planet formation theories predict that satellites should be a common outcome of the collisional dynamics in early extrasolar systems. Such satellites have the potential to unlock new avenues to learn about exoplanet systems, speaking to topics of habitability, tidal heating, planet formation, late-stage growth, planetary compositions, and more. Here we describe the results of our JWST program to search for Luna-analog exomoons around the rocky, habitable-zone M-dwarf planets TOI 700 d and e. We refine the ephemerides of both worlds, providing an order-of-magnitude improvement in period precision and a factor of 2-3 improvement in planetary radii. We identify a strong correlated noise signal with a timescale of $16\pm4$ minutes and an amplitude of $46\pm4$ ppm; similar signals have been observed in previous JWST analyses of other stars and have been ascribed to stellar granulation. This noise source inflates our error by a factor of 4 relative to photon-noise expectations in 10-minute bins and limits our sensitivity to moons: we determine that our observations are sensitive mainly to moons larger than Ganymede on periods longer than 2 days (i.e., moons larger than our solar system's natural satellites). If this noise could be corrected, we would be sensitive to Luna-analog moons. Future work to address this noise source will thus be critical for detecting exomoons in stellar transits, as well as for all other science cases that hope to take advantage of JWST white-light curves in the photon-noise limit.