Concerning the possible exomoons around Kepler-1625 b and Kepler-1708 b

arising from Heller, R. & Hippke, M. Nature Astronomy https://doi.org/10.1038/s41550-023-02148-w (2024)

Recently, Heller and Hippke¹ argued that the exomoon candidates Kepler-1625 b-i and Kepler-1708 b-i were allegedly ‘refuted’. In this Matters Arising, we address these claims. For Kepler-1625 b-i, we show that their Hubble light curve is identical to that previously published by the same lead author², in which the moon-like dip was recovered. Indeed, our fits of their data again recover this dip with improved residuals compared with the work of Heller and Hippke¹. Their fits therefore somehow missed this deeper likelihood maximum, producing apparently unconverged posteriors. Consequently, their best-fitting moon is the same radius as the planet, Kepler-1625 b-i, a radically different signal from that originally claimed³. The authors then inject this solution into the Kepler data and remark, as a point of concern, how retrievals obtain much higher significances than originally reported. However, this stems from the injection of a fundamentally different signal. We demonstrate that their Hubble light curve exhibits ~20% higher noise and discards 11% of the useful data, which compromises its ability to recover the subtle signal of Kepler-1625 b-i.