A new paper calculates how often stars stray into the Oort cloud, a vast, spherical shell of billions of icy objects that is thought to envelop our solar system. Such close encounters can dislodge these loosely orbiting comets, sending them hurtling into the solar system, risking a collision course with the Earth. So scientists believe they must spend most of their existence in an outer reservoir and get kicked inwards by passing stars. Theoretical models suggest the Oort cloud spans from as close as 2,000 astronomical units (1AU is the Earth-sun distance) to as far as 200,000 AU. Our sun completes one orbit in about 250m years, sometimes crossing the paths of other stars in brief stellar encounters.

Source: The Guardian August 31, 2017 17:15 UTC