Introduction to Comets

What are Comets?

Comets are simply any material that was left over from the formation of the solar system that orbit the sun, consisting of being made up of anything ranging from dust, ice, and rock. Comets are generally smaller in size than most above-average asteroids, spanning from a few kilometers wide to tens of kilometers wide. The orbits of comets around the Sun are also highly eccentric. 

In addition, a major characteristic of a comet is its distinguishable tail. This tail is formed when the comet’s orbit comes near the Sun and then it heats up and expels dust and gases. This trail of gases and dust usually follows the comet for millions of miles. 


Comets are classified according to their orbit shape/pattern. 

P – Periodic orbit

C – Non-periodic orbit

D – used (rarely) if a comet breaks up, disintegrates, or is lost after the initial discovery

X – used for comets where no orbit is known

A – object mistakenly identified as a comet, but actually a minor planet

I – Interstellar Object (i.e. Oumuamua)

Known Comets

Currently we know of 3,743 comets in our Solar System, but there are likely billions of comets in the Solar System (especially in the Kuiper Belt and Oort Cloud). 

Arguably the most famous comet in history is Halley’s Comet, a periodic, or “P”, comet that can be seen by people on Earth about every 75 years. The last time Halley’s Comet was seen from Earth was in 1986 and it is predicted to return again in 2061. 


“Comets.” NASA, NASA, 8 July 2021, 

Howell, Elizabeth. “Halley’s Comet: Facts about History’s Most Famous Comet.”, Space, 13 Jan. 2022, 

“List of Comets by Type.” Wikipedia, Wikimedia Foundation, 12 Mar. 2022,,%2C%20and%20D%20(lost). 

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