  Observations of the Kepler-1625 system with the Kepler and Hubble Space
Telescopes have suggested the presence of a candidate exomoon, Kepler-1625b I,
a Neptune-radius satellite orbiting a long-period Jovian planet. Here we
present a new analysis of the Hubble observations, using an independent data
reduction pipeline. We find that the transit light curve is well fit with a
planet-only model, with a best-fit $\chi^2_\nu$ equal to 1.01. The addition of
a moon does not significantly improve the fit quality. We compare our results
directly with the original light curve from Teachey & Kipping (2018), and find
that we obtain a better fit to the data using a model with fewer free
parameters (no moon). We discuss possible sources for the discrepancy in our
results, and conclude that the lunar transit signal found by Teachey & Kipping
(2018) was likely an artifact of the data reduction. This finding highlights
the need to develop independent pipelines to confirm results that push the
limits of measurement precision.
