Evidence for a Large Exomoon Orbiting Kepler-1625b

TL;DR

This study presents evidence suggesting the existence of a large exomoon orbiting Kepler-1625b, based on Hubble observations, photodynamical modeling, and timing deviations, highlighting the need for further monitoring to confirm the exomoon.

Contribution

First observational evidence supporting a large exomoon around Kepler-1625b using Hubble data and detailed modeling, advancing exomoon detection methods.

Findings

Evidence favors the exomoon hypothesis based on timing and flux data.

The exomoon is estimated to have a mass and radius similar to Neptune.

Further observations are needed to confirm the exomoon's existence.

Abstract

Exomoons are the natural satellites of planets orbiting stars outside our solar system, of which there are currently no confirmed examples. We present new observations of a candidate exomoon associated with Kepler-1625b using the Hubble Space Telescope to validate or refute the moon's presence. We find evidence in favor of the moon hypothesis, based on timing deviations and a flux decrement from the star consistent with a large transiting exomoon. Self-consistent photodynamical modeling suggests that the planet is likely several Jupiter masses, while the exomoon has a mass and radius similar to Neptune. Since our inference is dominated by a single but highly precise Hubble epoch, we advocate for future monitoring of the system to check model predictions and confirm repetition of the moon-like signal.