Separate orbital geometry from atmospheric asymmetry in spectroscopic transit analyses

Determine how to separate the effects of planetary orbital geometry from atmospheric asymmetry when the wavelength-dependent centroid of the effective planetary silhouette differs from the planet’s center of mass, thereby establishing a reliable reference for interpreting morning–evening atmospheric differences.

Background

The paper explains that spectroscopic transit analyses seek to infer atmospheric inhomogeneities, such as differences between the morning and evening terminators, from wavelength-dependent ingress and egress signals. These inferences require accurate knowledge of the planetary orbit, including the mid-transit time, because the orbit defines the reference point relative to which an atmospheric asymmetry is measured.

A further complication arises because the centroid of the effective silhouette can vary with wavelength and need not coincide with the planet’s center of mass. Consequently, orbital geometry and atmospheric asymmetry can produce partially confounded signatures. The paper identifies resolving this separation as an issue that has not yet been fully resolved in current analyses.