Simulations explain giant exoplanets with eccentric, close-in orbits

by University of California – Santa Cruz, Oct 30, 2019 in ScienceDaily

As planetary systems evolve, gravitational interactions between planets can fling some of them into eccentric elliptical orbits around the host star, or even out of the system altogether. Smaller planets should be more susceptible to this gravitational scattering, yet many gas giant exoplanets have been observed with eccentric orbits very different from the roughly circular orbits of the planets in our own solar system.

Surprisingly, the planets with the highest masses tend to be those with the highest eccentricities, even though the inertia of a larger mass should make it harder to budge from its initial orbit. This counter-intuitive observation prompted astronomers at UC Santa Cruz to explore the evolution of planetary systems using computer simulations. Their results, reported in a paper published in Astrophysical Journal Letters, suggest a crucial role for a giant-impacts phase in the evolution of high-mass planetary systems, leading to collisional growth of multiple giant planets with close-in orbits.