Comets are quite the celestial spectacle. Would you believe that they are simply pieces of dusty ice?
Specifically, comets are ball of frozen gases, rock and dust—that are often the size of a small town! Think of comets as comic snowballs—or, some people jokingly refer to comets as dirty snowballs.
Image: Comet Giacobini-Zinner on 31 October 1998. Credit: N.A.Sharp/NOAO/AURA/NSF
Comets orbit the sun. Jets of gas and dust from comets form long tails that can be seen from Earth.
When a comet flies close to the Sun, it heats up and spews dust and gases. Some of its ice turns into a giant glowing head larger than most planets. The dust and gases form a long, bright trail, or tail, of vapor that stretches away from the Sun for millions of kilometers. That tail is a comet’s most amazing feature.
This image of comet Encke was taken in Jauerling (lower Austria) in May of 2014. Credit: Gerald Rhemann/NASA.
Comets may not be able to support life themselves, but they may have brought water and organic compounds—the building blocks of life—through collisions with Earth and other bodies in our solar system.
As Almanac astronomer Bob Berman says, “Comets are relics of the birth of the solar system around 4.6 billion years ago. Comets are part of the original material that made up the solar system.”
Why do see we green comets? They are not common, but the green is caused by dark organic matter on the comet itself! You won’t find this on an astroid.
Most comets are unpredictable. Over the centuries, people were both awed and alarmed by comets because of this unpredictability—as if they were stars that suddenly appeared in the sky. Can you imagine a snowball over a mile wide appearing above your head?
Through the ages, comets were omens and portends—usually of doom and death and bad things. Comets were not good! Remember that it was a comet that probably wiped out the dinosaurs on Earth. That said, comets have also been taken as good omens by some historic figures, such a William the Conquerer.
Landing on a Comet!
In 2014, European Space Agency proble Rosetta (named after the famous Rosetta Stone) landed successfully on a comet—Comet 67P/Churyumov–Gerasimenko (67P). Below are some amazing images of the comet. All credit goes to ESA/Rosetta/NAVCAM, CC BY-SA IGO 3.0.
Rosetta “selfie” at Mars
Rosetta’s image of Comet 67P with a tail of gas and dust, as it orbits the comet from 162 km (101 mi) away.
Rosettta’s image of Comet 67P as it orbits the comet from 10 km (6 mi) away.
Learn more about the Rosetta mission on the European Space Agency web site here.
What are Meteor Showers? See our page with Meteor Shower facts.