Comets

Comets are among the most striking and dynamic objects in the Solar System. They’re spectacularly beautiful, but they’re also scientifically invaluable — preserving the most primitive ices and dust from the early Solar Nebula. In fact, they may even have delivered much of Earth’s water and some of the organic molecules essential for life.

Learning Activity

Watch the video and find answers to these six questions:

  • What are the similarities and differences between comets and asteroids? (You may also want to watch this companion video.)
  • What types of ice do we find in comets?
  • What are the three main parts of a comet, where does the name “comet” come from, and what causes them to evolve as they orbit the Sun?
  • If comets evaporate when they come close to the Sun, how can they be billions of years old? Where do short-period and long-period comets come from? (This answer isn’t given explicitly in the video, but you can work it out from what you learned in Module 9. For help, see this optional video.)
  • What does the evidence from missions to Halley’s Comet and from ESA’s Rosetta mission to comet 67P/Churyumov-Gerasimenko tell us about the evolution of short-period comets?
  • How might comets have contributed to the origin of life on Earth, and what evidence supports this idea?

Note: Since this video was produced, additional missions such as NASA’s Stardust (sample return from comet Wild 2) and Deep Impact (impact study of Tempel 1) have complemented Rosetta’s close-up observations. Together, these missions have shown that comets contain complex organic molecules — including amino-acid precursors — strengthening the link between cometary chemistry and the early conditions for life on Earth.