By the turn of the 20th century, it was understood that there were two main classes of comet: short-period comets (also called See more

The Oort cloud is thought to have developed after the formation of planets from the primordial protoplanetary disc approximately 4.6 … See more

Most of the comets seen close to the Sun seem to have reached their current positions through gravitational perturbation of the Oort cloud by the tidal force exerted by the See more

Space probes have yet to reach the area of the Oort cloud. Voyager 1, the once fastest and farthest of the interplanetary space probes … See more

The Oort cloud is thought to occupy a vast space somewhere between 2,000 and 5,000 AU (0.03 and 0.08 ly) from the Sun to as far out as 50,000 AU (0.79 ly) or even 100,000 to … See more

Comets are thought to have two separate points of origin in the Solar System. Short-period comets (those with orbits of up to 200 years) are … See more

Besides the galactic tide, the main trigger for sending comets into the inner Solar System is thought to be interaction between the Sun's … See more