Probable Spin-Orbit Aligned Super-Earth Planet Candidate KOI-2138.01

TL;DR

This study uses rotational gravity darkening to measure the low spin-orbit misalignment of a super-Earth exoplanet, providing insights into planetary system architectures.

Contribution

It presents the first aligned super-Earth with a measured spin-orbit angle, using gravity darkening, expanding understanding of planetary orbital alignments.

Findings

KOI-2138.01 has a low projected spin-orbit angle of 1°±13°.

It is the second super-Earth with a measured spin-orbit alignment.

The planet's orbital period suggests potential for similar systems with terrestrial planets.

Abstract

We use rotational gravity darkening in the disk of \emph{Kepler} star KOI-2138 to show that the orbit of $2.1-R_\oplus$ transiting planet candidate KOI-2138.01 has a low projected spin-orbit alignment of $\lambda=1^\circ\pm13$. KOI-2138.01 is just the second super-Earth with a measured spin-orbit alignment after 55 Cancri e, and the first to be aligned. With a 23.55-day orbital period, KOI-2138.01 may represent the tip of a future iceberg of solar-system-like terrestrial planets having intermediate periods and low-inclination circular orbits.