Mounting discoveries of extrasolar planets orbiting post‐main‐sequence stars motivate studies to understand the fate of these planets. In the traditional ‘adiabatic’ approximation, a secondary’s eccentricity remains constant during stellar mass‐loss. Here, we remove this approximation, investigate the full two‐body point‐mass problem with isotropic mass‐loss, and illustrate the resulting dynamical evolution. The magnitude and duration of a star’s mass‐loss combined with a secondary’s initial orbital characteristics might provoke ejection, modest eccentricity pumping, or even circularization of the orbit. We conclude that Oort Clouds and wide‐separation planets may be dynamically ejected from 1–7 M⊙ parent stars during AGB evolution. The vast majority of planetary material that survives a supernova from a 7–20 M⊙ progenitor will be dynamically ejected from the system, placing limits on the existence of first‐generation pulsar planets. Planets around >20 M⊙ black hole progenitors may easily survive or readily be ejected depending on the core collapse and superwind models applied. Material ejected during stellar evolution might contribute significantly to the free‐floating planetary population.

ABSTRACT25-50 per cent of all white dwarfs (WDs) host observable and dynamically active remnant planetary systems based on the presence of close-in circumstellar dust and gas and photospheric metal pollution. Currently accepted theoretical explanations for the origin of this matter include asteroids that survive the star's giant branch evolution at au-scale distances and are subsequently perturbed on to WD-grazing orbits following stellar mass-loss. In this work, we investigate the tidal disruption of these highly eccentric (e > 0.98) asteroids as they approach and tidally disrupt around the WD. We analytically compute the disruption time-scale and compare the result with fully self-consistent numerical simulations of rubble piles by using the N-body code PKDGRAV. We find that this time-scale is highly dependent on the orbit's pericentre and largely independent of its semimajor axis. We establish that spherical asteroids readily break up and form highly eccentric collisionless rings, which do not accrete on to the WD without additional forces such as radiation or sublimation. This finding highlights the critical importance of such forces in the physics of WD planetary systems.

Exoplanets have been observed at many stages of their host star's life, including the main sequence (MS), subgiant and red giant branch stages. Also, polluted white dwarfs (WDs) likely represent dynamically active systems at late times. Here, we perform 3-body simulations which include realistic post-MS stellar mass loss and span the entire lifetime of exosystems with two massive planets, from the endpoint of formation to several Gyr into the WD phase of the host star. We find that both MS and WD systems experience ejections and star-planet collisions (Lagrange instability) even if the planet-planet separation well-exceeds the analytical orbit-crossing (Hill instability) boundary. Consequently, MS-stable planets do not need to be closely-packed to experience instability during the WD phase. This instability may pollute the WD directly through collisions, or, more likely, indirectly through increased scattering of smaller bodies such as asteroids or comets. Our simulations show that this instability occurs predominately between tens of Myr to a few Gyrs of WD cooling.A planet's life may be split into four distinct stages: 1) formation and concurrent dynamical excitation, 2) main sequence (MS) evolution, 3) evolution during post-MS stellar phase changes, and 4) white dwarf (WD) evolution. The first stage generally lasts no longer than 0.1% of the entire MS lifetime. The second stage is relatively dynamically quiescent, with only occasional but often important scattering interactions. In the third stage, the planet is subject to dynamical changes due to the star's violent actions as it becomes a giant. In the final stage, the star has become a WD, and the planet again enters and remains in a phase of relative dynamical quiescence occasionally punctuated by scattering interactions or external forcing. This general picture, which does not include possibilities such as the capture of free-floating planets, planetary destruction due to supernovae, or multiple host stars, describes the life cycle of the vast majority of known exoplanets.The volume of planetary literature investigating the ⋆