Where Do Comets Come From?

What is a Comet?

Comets are bodies made of rock, dust and ice that orbit the sun within our solar system. They range in size from just a hundred meters to several kilometers across. What separates a comet from an asteroid is that comets are rather loosely packed together, as opposed to asteroids, which are more or less a solid rock in space. Comets trail debris behind them, especially when they approach the sun and heat up, leaving a visible tail of vaporized gas, dust and rocky matter behind them. Comets also have long, elliptical orbits and are drawn from deep space and into the solar system by gravitation.

The Kuiper Belt

One of the places comets are thought to originate from is the Kuiper Belt. The Kuiper Belt is similar to the asteroid belt between Mars and Jupiter, but far larger, extending from beyond the orbit of Neptune to far outside the solar system. Pluto resides inside the Kuiper Belt, and is mostly made up of leftovers from the creation of the solar system. Comets from the Kuiper Belt tend to have short orbits (less than 200 years), and are typically rockier and/or dustier than other comets.

The Oort Cloud

Another source of comets is the Oort Cloud, which is much further away, being one light-year from the sun and therefore fully in interstellar space. The Oort Cloud is thought to be dotted with potential comets, mostly made from water, ammonia and methane ice. These comets tend to have a long orbital period. While defined as more than 200 years, the orbital period can extend into thousands or even millions of years. The Oort Cloud is also the theorized source of single-apparition comets; these have hyperbolic orbits that carry them straight out of the solar system following a single pass.