GEOL 212 Lecture Notes - Lecture 60: Protoplanetary Nebula, Jan Oort, Scattered Disc
27 Dec 2017
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Document Summary
In terms of orbits, there are two distinct groups of comets: we have discussed short- period comets, most comets have much longer orbital periods, such that their periodicity can"t be studied on the time scale of human history. These are the long-period comets: their orbits have semimajor axes of hundreds or even thousands of au, can have any inclination, are as likely to be retrograde as prograde. The nature of the orbits reveals two different sources for comets: short-period comets derive from the outer kuiper belt, long period comets come from the oort cloud, a diffuse spherical region enclosing the solar system at great distances. The oort cloud was first proposed in 1950 by jan oort, a dutch astronomer, based on the observation that long period comets can enter the solar system from any direction, and from calculations of their apoapses.
