Close encounters of the stellar kind / Gaia / Space Science / Our Activities / ESA
http://www.esa.int/Our_Activities/Space_Science/Gaia/Close_encounters_of_the_stellar_kind
The movements of more than 300 000 stars surveyed by ESA’s Gaia satellite reveal that rare close encounters with our Sun
might disturb the cloud of comets at the far reaches of our Solar System, sending some towards Earth in the distant future.
As the Solar System moves through the Galaxy, and as other stars move on their own paths, close encounters are inevitable –
though ‘close’ still means many trillions of kilometres.
A star, depending on its mass and speed, would need to get within about 60 trillion kilometres before it starts to have an
effect on the Solar System’s distant reservoir of comets, the Oort Cloud, which is thought to extend out to 15 trillion
kilometres from the Sun, 100 000 times the Sun–Earth distance.
For comparison, the outermost planet Neptune orbits at an average distance of about 4.5 billion kilometres, or 30 Sun–Earth
distances. The gravitational influence of stars that pass near the Oort Cloud could perturb the paths of comets residing there,
jolting them onto orbits that bring them in to the inner Solar System.
While this is thought to be responsible for some of the comets that appear in our skies every hundred to thousand years,
it also has the potential to put comets on a collision course with Earth or other planets.
Tracking stellar motions
https://www.youtube.com/watch?v=KCEr8PqeLWI