What is the Oort cloud?
Cometary periods range from a few years to even ten million years. It is believed
that most of the long period comets emanate from a region extending beyond the orbit of Pluto to a distance of some 100,000 a.u. which contains the bulk of the comets in the Solar System.
According to the currently accepted theory, there are at least a trillion long period comets in this region referred to as the Oort cloud. Comets in the Oort cloud cannot be detected from Earth. The only comets visible from Earth are those that have highly eccentric orbits which brings them near the Sun.
What causes a comet to swerve from the Oort cloud towards the Sun?
According to the currently accepted theory, passing stars and interstellar clouds quite often disturb the equilibrium of the Oort cloud making some comets change their circular orbits and come near the Sun.
It remains a perpetual phenomenon with old comets dying out and new ones displaced from the Oort cloud appearing.
Name the space-probe that made a rendezvous with two comets.
Space probe Giotto was launched from Earth in 1985 on a fifteen-year mission. In 1986 it flew 600 km of the nucleus of Halley’s Comet, and in 1992 within 200 km of Grig-Skjellerup comet. It flew past Erath in 1990.
