A mysterious visitor from another solar system could be an alien spacecraft, according to a leading Harvard astronomer.

We investigate the kinematic evolution of planetesimals in self-gravitating discs, combining smoothed particle hydrodynamical (SPH) simulations of the disc gas with a gravitationally coupled ...

In a multiplanet system, when orbital precession is fast enough to resonate with the orbital motion of a distant binary companion, the results range from excitation of large planetary ...