  Transmission spectroscopy is one of the most successful methods of learning
about exoplanet atmospheres. The process of retrievals using transmission
spectroscopy consists of creating numerous forward models and comparing them to
observations to solve the inverse problem of constraining the atmospheric
properties of exoplanets. We explore the impact of one simplifying assumption
commonly employed by forward models of transiting exoplanets: namely that the
planet can be treated as an isolated, non-rotating spherical body. The
centrifugal acceleration due to a planet's rotation opposes the gravitational
pull on a planet's atmosphere and increases its scale height. Conventional
forward models used for retrievals generally do not include this effect. We
find that atmospheric retrievals produce significantly different results for
close-in planets with low gravity when this assumption is removed, e.g.,
differences between true and retrieved values of gas abundances greater than
1$\sigma$ for a simulated planet analogous to WASP-19 b. We recommend that the
correction to the atmospheric scale height due to this effect be taken into
account for the analysis of high precision transmission spectra of exoplanets
in the future, most immediately JWST Cycle 1 targets WASP-19 b and WASP-121 b.
