Asteroids and comets were formed about 4.5 billion years ago, with asteroid orbits taking between three and six years, while comets can spend thousands or even millions of years in the solar system before returning to the sun.
The duration of planetary orbits varies widely – Earth takes 365 days, Saturn takes 10,759 days (29.4 years), Neptune takes 60,190 days (164.9 years), contrasted with comets such as Hyakutake with orbital periods of 40,000 years.
While planetary and asteroid orbits are almost circular and stable, comets can have highly eccentric or squashed orbits, with some 'long-period comets' having orbital periods of over 200 years, hinting at their origin from the distant Oort Cloud.
Long-period comets can have highly inclined orbits to the ecliptic, suggesting their origin from the Oort Cloud, located about 100,000 astronomical units (AU) from the sun.
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