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.
What It Would Be Like to Live On a Comet
Halley’s Comet, named after astronomer Edmond Halley, last visited the inner solar system in 1986, and will return in 2061.
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).
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.
Source SPACE.com: All about our solar system, outer space and exploration.
Source: http://www.space.com/29025-living-on-comets-facts-infographic.html