  The discovery of terrestrial exoplanets is uncovering increasingly diverse
architectures. Of particular interest are those systems that contain exoplanets
at a variety of star-planet separations, allowing direct comparison of
exoplanet evolution (comparative planetology). The Kepler-1649 system contains
two terrestrial planets similar both in size and insolation flux to Venus and
Earth, although their eccentricities remain largely unconstrained. Here we
present results of dynamical studies of the system and the potential effects on
climate. The eccentricities of the Kepler-1649 system are poorly constrained,
and we show that there are dynamically viable regions for further terrestrial
planets in between the two known planets for a limited range of eccentricities.
We investigate the effect of eccentricity of the outer planet on the dynamics
of both planets and show that this results in high-frequency (1000-3000 year)
eccentricity oscillations in long-term stable configurations. We calculate the
resulting effect of these eccentricity variations on insolation flux and
present the results of 3D climate simulations for the habitable zone planet.
Our simulations demonstrate that, despite large eccentricity variations, the
planet can maintain stable climates with relatively small temperature
variations on the substellar hemisphere for a variety of initial climate
configurations. Such systems thus provide key opportunities to explore
alternative Venus/Earth climate evolution scenarios.
