Swell Comet
When they are far from the Sun, most comets are insignificant specks less than 10 km (6 miles) across. But when a comet gets close to the Sun, the cloud of gases surrounding it can swell larger than the size of Jupiter - more than 10 times the diameter of Earth. Comets also sprout beautiful tails that stretch for millions of kilometers away from the Sun.

One Tough Robot
No one expected Europe's Giotto spacecraft to survive the beating it took from dust and rocks when it made a close pass by Comet Halley in 1986. Damaged, but far from dead, Giotto flew on to study a second comet.

Thar She Blows
Comet Hale-Bopp spewed out about 250 tons of gas and dust per second - more than 50 times what most other comets churn out. It made for a spectacular show as it passed through the inner solar system in 1997.

Don't Wait Up
Comet Hale-Bopp won't return to our skies for about 2,740 years - and that's not even close to the longest orbit comets make around our Sun. Some far travelers take millions of years to make one orbit. Others, such as Comet Encke, run by the Sun every few years.

Hang On
If you weigh 45 kilograms (100 pounds) on Earth, you'd weigh only about 0.005 kilograms (0.01 pounds) on a comet. Although we don't recommend it, you could easily jump right off into space. If you rode a comet close to the Sun, you'd probably get blown into space on a jet of dust and gas.

Killer Comet?
Were the dinosaurs wiped out by a comet impact 65 million years ago? It's possible. In the earliest days of the solar system, comets regularly bombarded the planets. And a comet smashed into Jupiter as recently as 1994.