【英语时差8,16】奥尔特云与彗星（下）（在线收听）

The Oort cloud is a spherical haze of comets that surrounds our entire solar system. We often get the false impression that the solar system ends with Pluto. In fact, beyond Pluto is the Oort cloud, encircling everything else like an enormous shell. It’s so far out it’s halfway to the next star, and almost beyond the reach of our sun’s gravity. Why Do We See Comets Zooming By? So if the Oort cloud is so far away, why do we see comets zooming past earth from time to time? Passing stars do it. Another star passing through the Oort cloud, or just near it, will disturb lots of comets, sometimes causing them to go flying inward toward the planets. So you could say that other stars throw snowballs at us from time to time.