A comet is a mountain of ice and dust, tumbling through space. When a comet approaches the sun, its ices sublimate (turn from solid to gas). Vapor, dust and gases stream out to form a hazy tail behind the comet.
Halley's gravity is so low, an object dropped from chest height would take two minutes to fall to the surface. When close to the sun, Halley's surface temperature can reach 170 degrees Fahrenheit (77 degrees Celsius). [Take Our Comet Quiz]
Comet Halley has an elongated orbit that takes it from out beyond Neptune to closer to the sun than Venus's orbit. Halley is a "dirty snowball" containing dust, ice, carbon dioxide, ammonia, methane and more.
Read our full special report:
Living on Other Planets: What Would It Be Like?
Find out what it might be like to live on other worlds in our solar system, from Mercury to Pluto and beyond in our 12-part series.
- Capturing Halley's Comet: An Astronomy Tale
- Photos: Spectacular Comet Views from Earth and Space
- Halley's Comet Legacy: Photos of Eta Aquarid Meteor Shower