  The planetary mass and radius sensitivity of exoplanet discovery capabilities
has reached into the terrestrial regime. The focus of such investigations is to
search within the Habitable Zone where a modern Earth-like atmosphere may be a
viable comparison. However, the detection bias of the transit and radial
velocity methods lies close to the host star where the received flux at the
planet may push the atmosphere into a runaway greenhouse state. One such
exoplanet discovery, Kepler-1649b, receives a similar flux from its star as
modern Venus does from the Sun, and so was categorized as a possible exoVenus.
Here we discuss the planetary parameters of Kepler-1649b with relation to Venus
to establish its potential as a Venus analog. We utilize the general
circulation model ROCKE-3D to simulate the evolution of the surface temperature
of Kepler-1649b under various assumptions, including relative atmospheric
abundances. We show that in all our simulations the atmospheric model rapidly
diverges from temperate surface conditions towards a runaway greenhouse with
rapidly escalating surface temperatures. We calculate transmission spectra for
the evolved atmosphere and discuss these spectra within the context of the
James Webb Space Telescope (JWST) Near-Infrared Spectrograph (NIRSpec)
capabilities. We thus demonstrate the detectability of the key atmospheric
signatures of possible runaway greenhouse transition states and outline the
future prospects of characterizing potential Venus analogs.
