TOI-3884~b is an unusual 6.4~R⊕ planet orbiting an M4 host, whose transits display large and persistent spot-crossing events. We used the \textit{Tierras} Observatory to monitor both the long-term photometric variability of TOI-3884 and changes in the spot-crossing events across multiple transits of the planet. We show that the star rotates with a period of 11.020±0.015~days. We simultaneously model the rotational modulation of the star and variations in transit shapes that arise due to rotation of the spot, allowing us to determine the true stellar obliquity, ψ⋆. The data are best described by a planet on a misaligned orbit around a highly inclined star (ψ⋆=77.4∘−2.5∘+2.3∘; i⋆=22.3∘−1.6∘+1.8∘) that hosts a large polar starspot (rspot=31.2∘−1.9∘+2.4∘; λspot=80.5∘±1.2∘). Archival photometry from the Zwicky Transient Facility suggests that this polar spot has persisted on TOI-3884 for at least seven years. The TOI-3884 system provides a benchmark for studying the evolution of a polar spot on an M dwarf.
@article{arxiv.2506.11998,
title = {Spot-Crossing Variations Confirm a Misaligned Orbit for a Planet Transiting an M Dwarf},
author = {Patrick Tamburo and Samuel W. Yee and Juliana García-Mejía and David Charbonneau and Allyson Bieryla and Karen A. Collins and Avi Shporer},
journal= {arXiv preprint arXiv:2506.11998},
year = {2025}
}