Dirty Snowballs in Summer: Comets!

Dr. Teri Gee, Barlow Planetarium Director
Apr 30, 2024
2 min read

Updated: Jun 6

*Pictured: the 12P/Pons-Brooks Comet in our sky right now!*

Do you like snowballs in the summertime?

I’m not talking about from your backyard, but rather, I’m talking about cosmic dirty snowballs. Specifically, I’m talking about COMETS! You might be thinking of the normal pictures of comets and wondering why we call them dirty snowballs. They’re beautiful and glowing. Not dirty-looking at all!

Comets normally live out in the far reaches of our solar system, mostly in two areas: the Kuiper Belt and the Oort Cloud. Now, those names might seem strange, but they’re actually named after astronomers who did some of the first research about those parts of the solar system. Comets only come into the inner solar system when something knocks them out of their usual orbit. Some comets are now on regular orbits into the inner solar system and around the Sun. Others come into the inner solar system and then break up because of the heat of the Sun. Still others come into the inner solar system and then leave, never to return.

When comets are out in the Kuiper Belt or the Oort Cloud, they don’t have tails! Instead, they are frozen chunks of water and ice combined with dust, rock and other materials called “volatiles” like carbon dioxide or methane. They orbit around the Sun almost undetected until they get nudged out of their orbit and head toward the Sun. The closer they get, the hotter it gets. All that ice starts to vaporize, or turns into gas, forming the glowing coma and the tail, which always points away from the Sun.

There’s actually a comet in our sky right now! It’s called 12P/Pons-Brooks and, in the picture, you can see the glowing coma or head and the diffuse tail streaming behind. The comet reached its closest approach to the Sun on April 21, but it will reach its closest approach to us on June 2. It’s possible that it might be bright enough to see with your own eyes or binoculars, so keep watching! Maybe you’ll be able to see this dirty snowball as it heads back out into the Kuiper Belt once more.