How might a planet between Mars and Jupiter influence the inner solar system? effects on orbital motion, obliquity, and eccentricity

As implied by exoplanet population censuses, super-Earths are extremely common in the galaxy. In the solar system, models suggest that the formation of an Earth-to-super-Earth mass planet could have readily occurred in the inner regions ($<3$ AU) if such body is able to survive the early intense and chaotic intertaction episodes of the Jovian worlds with the rest of the solar system. In this study, we test the consequences of such a hypothesis using a three-dimensional (3D) N-Rigid-Body integrator. With a 3D model in which the planet is modeled as a rigid body to account for its finite size and rotation, we simulate the orbital evolution of the three inner terrestrial planets over 2 Myr periods. Our results show that an additional super-Earth sized planet between 2 and 3.5 AU would have (i) destabilized Earth’s orbit over timescales of 1-2 Myrs, (ii) increased Mars’s obliquity by $\sim 55°$, and (iii) perturbed the eccentricity of Venus by up to $e\sim 0.4$. Our study explores an “alternate fate” of the terrestrial planets and our results suggest that the formation of a super-Earth in the inner solar system would have exerted grave consequences for the orbital dynamics and habitability of the terrestrial planets.