Long-Period Comet

Comet McNaught from Australia in 2007. Image source: www.pbs.org, Akira Fujii

Comets with orbital periods longer than 200 years, often with highly elliptical orbits highly inclined to the ecliptic. These comets probably were perturbed from orbits in the Oort cloud by a passing star or giant molecular cloud, or by tidal forces generated by the bulge and disk of our Galaxy. The high inclinations of the orbits arise since they can enter the inner Solar System from any angle. Long-period comets tend to be the most spectacular comets; because they have not made many (if any) passes through the inner Solar System, and still retain a large percentage of their initial volatiles. Sublimation of these volatiles from the comet nucleus as it nears the Sun produces the coma and highly-visible tail. Comets Hale-Bopp (1997), Hyakutake (1996), and McNaught (2007), shown below, were long-period comets.

Some or all content above used with permission from J. H. Wittke.