Orbit Perturbations of Habitable Zone Planets Due To Inner Planetary Companions

We investigate the degree of orbit perturbations from confirmed planetary companions on known planets that reside in their host star’s habitable zone. The traditional definition of the habitable zone (HZ) is the range of distances from a star that includes an Earth-like planet where the climate is stable enough for water to be, but this definition does not yet consider the effects on habitability due to orbit perturbations from neighboring planets. This research includes the effects perturbers have on a HZ planet for observed systems. Using orbit and planet parameters of confirmed exoplanets residing in multi-planet systems and traditional HZ considerations, we identify the number of observed planets that are potentially habitable. There are 87 HZ planets using conservative considerations and 113 HZ planets using optimistic considerations. We semi-analytically estimate the degree of dynamical stability for these HZ planets, particularly for planets residing in the inner portions of the HZ. Using optimistic HZ considerations, two Kepler systems, K2-3 and GJ3293, were numerically simulated to analyze the orbits of the HZ planets due to their perturbers, and we estimate the resulting timescales and magnitude of the change in instellation on the HZ planets due to perturbers. If the planets are on low eccentricity orbits, the HZ planets in these systems stayed in the traditionally defined HZ and the change in eccentricity is small.