DOI: 10.5061/dryad.zs7h44jh4
title: Concerning the possible exomoons around Kepler-1625b and Kepler-1708b

description: Recently, Heller & Hippke 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, we show
 that their Hubble light curve is identical to that previously published by
 the same lead author, in which the moon-like dip was recovered. Indeed,
 our fits of their data again recover the moon-like dip with improved
 residuals than that obtained by Heller & Hippke. Their fits
 therefore appear to have somehow missed this deeper likelihood maximum, as
 well producing apparently unconverged posteriors. Consequently, their
 best-fitting moon is the same radius as the planet, Kepler-1625 b; a
 radically different signal from that which was originally claimed. 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 issue 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. For Kepler-1708 b-i it was claimed that the exomoon model's
 Bayes factor is highly sensitive to detrending choices, yielding reduced
 evidence with a biweight filter versus the original claim. We use their
 own i) detrended light curve and ii) biweight filter code to investigate
 these claims. For both, we recover the original moon signal, to even
 higher confidence than before. The discrepancy is explained by comparing
 to their quoted fit metrics, where we again demonstrate that the Heller
 & Hippke regression definitively missed the deeper likelihood
 maximum corresponding to Kepler-1708 b-i. We conclude that both candidates
 remain viable but certainly demand further observations. The following
 archive contains the files used to generate the figures, including scripts
 used, as well as the actual data and related products used in the
 analysis. The README file provides details on the contents.
description: Data behind the figures, analysis and tables in Kipping et al. (2025)
 [https://doi.org/10.5061/dryad.zs7h44jh4](https://doi.org/10.5061/dryad.zs7h44jh4) ## === Description of the data and file structure === Each folder contains files concerning specific tasks. In reference to the folder name, "H19" refers to the paper bibcode 2019A&A...624A..95H, "HH23" refers to the paper bibcode 2023NatAs.tmp..258H, K22 refers to the paper bibcode 2022NatAs...6..367K and TK18 refers to the paper bibcode 2018SciA....4.1784T. ### Extraction folders The extraction folders (*_extraction/) contain one or more notebooks that outline the extraction process, coupled to the relevant files needed in each folder. Within each, the file formats are: **HST_H19** * HST_H19_extraction/H19_Fig2h_bestfitline.csv: time (d), relative flux * HST_H19_extraction/H19_Fig2h_rawextraction.csv: time (d), relative flux * HST_H19_extraction/H19_HST_WFC3.dat: time (d), relative flux, error on relative flux **HST_HH23** * HST_HH23_extraction/HH23_Fig1d_rawextraction.csv: time (d), relative flux * HST_HH23_extraction/HH23_Fig1l_rawextraction.csv: time (d), relative flux * HST_HH23_extraction/HH23_HST_WFC3_residuals.dat: time (d), relative flux, error on relative flux * HST_HH23_extraction/HH23_HST_WFC3.dat: time (d), relative flux, error on relative flux * HST_HH23_extraction/TK18_HST_WFC3.dat: time (d), relative flux, error on relative flux **Kep_HH23** * Kep_HH23_extraction/HH23_Fig3a_rawextraction.csv: time (d), relative flux * Kep_HH23_extraction/HH23_Fig3b_rawextraction.csv: time (d), relative flux * Kep_HH23_extraction/HH23_Kep_v1.dat: time (d), relative flux, error on relative flux * Kep_HH23_extraction/HH23_Kep_v3c.dat: time (d), relative flux, error on relative flux * Kep_HH23_extraction/HH23_Kep_v3d.dat: time (d), relative flux, error on relative flux * Kep_HH23_extraction/K22_AVG.dat: time (d), relative flux, error on relative flux * Kep_HH23_extraction/kplr007906827-2011073133259_llc.dat: time (d), SAP flux, error on SAP flux, PDC flux, error on PDC flux, error flag * Kep_HH23_extraction/kplr007906827-2013098041711_llc.dat: time (d), SAP flux, error on SAP flux, PDC flux, error on PDC flux, error flag ### HST\_intraorbit\_RMS\_comparison/ This contains the files and scripts needed to compute the median intra-orbit root-mean-square of contrasting data sets. All the files have the same first three column formats: time (d), relative intensity, error on relative intensity ### H19\_vs\_HH23\_HST\_comparison/ This contains a Mathematica notebook comparing two light curve extractions contained within that folder, H19_HST_WFC3.dat and HH23_HST_WFC3.dat. These are the H19 and HH23 reductions of Kepler-1625b's HST WFC3 light curve, with the columns representing: time (d), relative flux, error on relative flux ### Ext\_Data\_Fig3/ This contains a Jupyter notebook that was used to generate Extended Data Figure 3. ### Fit folders (\_fits/) These contain the output files from MultiNest regressions unaltered by our team (see [https://github.com/farhanferoz/MultiNest/blob/master/README.md](https://github.com/farhanferoz/MultiNest/blob/master/README.md) for file formats), included some additional analysis notebooks our team generated. The sub-folders, M_chromatic, P_chromatic and Z_chromatic refer to planet+moon model, planet-only model, and zero-radius moon-model, respectively (where the chromatic term just emphasises the distinct geometric depth and limb darkening coefficients allowed for between bands). For the planet-only model (LRVplan), the 7 free parameter solutions regressed as Rp/R*, rho*, b, P, tmid, q1, q2. For the LRVmoon models, these are the same but we append Ps, asp/p, phi_s, cos(is), Omega_s, Ms/Mp and Rs/Rp (14 in total). **K1708_fits/K22_injections/*.dat** contains injected planet-only light curves into the real Kepler data, which are then detrended using i) CoFiAM ii) local linear regression iii) polynomials using a) SAP data b) PDC data - giving a total of six data products for the two injected epochs. These are then method marginalized ("AVG" filenames). The bash shell scripts used for the detrending are also left in the folder for reproducibility. In each of the 22 injected folder ("1" -&gt; "22") one can find these files, as well as a fits/ subfolder containing the same MultiNest outputs as before. ## === Sharing/Access information === Data was derived from the following sources: Kipping et al. (2025), Nature Matters Arising, accepted ## === Code/Software === Contains shell and Mathematica scripts. MultiNest (Feroz et al. 2009) used for regressions [see [https://github.com/farhanferoz/MultiNest](https://github.com/farhanferoz/MultiNest)]