Where and how do comets originate?

   The most commonly accepted theory about where comets originate was suggested by Dutch astronomer Jan Hendrick Oort in 1950. Oort's theory states that trillions of inactive comets lie on the outskirts of the solar system, about one light-year from the Sun. They remain there in what is called an Oort cloud, until a passing gas cloud or star jolts a comet into orbit around the Sun. The Oort cloud lies somewhere between 50,000 and 150,000 astronomical units (AU) from the Sun. In 1951, another Dutch as­tronomer, Gerard Kuiper, suggested that there is a second cometary reservoir located just beyond the edge of our solar system, around one thousand times closer to the Sun than the Oort cloud. His hypothetical Kuiper belt is located somewhere between 35 and 1,000 AU from the Sun. It contains an estimated ten million to one billion comets, far fewer than the Oort cloud.