Orbital perturbations caused by passing stars might very well have caused past extinctions
According to new computer simulations, scientists now think that any calculations of the long term changes in the orbits of the planets in our solar system must include the orbital perturbations caused by passing stars, perturbations that might very well have caused past extinctions. From their paper’s introduction:
Simulations of the long-term orbital evolution of the Sun’s planets have nearly always modeled the solar system as an isolated system. For many purposes, this is a very good approximation, but the solar system is of course part of the Milky Way Galaxy. Consequently, it occasionally suffers close encounters with other field stars, and solar neighborhood kinematic studies predict an average of ∼20 stellar passages within 1 [parsec] of the Sun each [million years].
Because the solar system cross section scales with the square of heliocentric distance, the large majority of these encounters will be distant and inconsequential to the planets’ dynamics, but this is not guaranteed. In fact, there is a ∼0.5% chance that a field star passage will trigger the loss of one or more planets over the next 5 [billion years], and such passages may actually guarantee the disruption of the planets’ orbits many [billion years] after the Sun becomes a white dwarf. Yet, encounters need not trigger an instability for them to have dynamical consequences for the planets. For instance, it has been suggested that ∼one-third of Neptune’s modern eccentricity has been generated through past stellar encounters, but many of the long-term dynamical effects of stellar passages remain unknown.
Their simulations as well as other data suggest that for computer models to have any chance of accurately calculating the orbital evolution of the solar system’s planets, those models must include the passing of nearby stars.
Or to put it in more blunt terms, the uncertainties here are so great that it is unlikely any computer model will ever be able to reconstruct our solar system going back further than 50 million years.