Asked by: Dave White, Portland, USA
Unlike planets, stars seem fixed in the night sky. Yet in reality, they too are moving through space: their vast distance means it just takes a long time for their movement to become obvious.
Over the long history of the Solar System, countless stars have approached our planetary neighbourhood. While there’s no evidence of a direct collision, the orbits of the outer planets are thought to have changed dramatically during the early history of the Solar System. It’s possible that this was due to gravitational jostling among the planets themselves, but a stellar intruder can’t be ruled out.
Even a ‘near miss’ could have devastating consequences. Far beyond the known planets lies a vast collection of icy debris and comets surrounding the Sun known as the Oort Cloud. A star passing even a light-year or so away from us could stir these up, hurling cosmic missiles at the planets.
To assess the risk, astronomers at the Max Planck Institute for Astronomy, Germany, recently published an analysis of the movement of over seven million stars. Fortunately, they found just one – codenamed Gliese 710 – likely to disturb the Oort Cloud over the next million years or so.