PHOTO COURTESY OF JPL

With their bright "hairy" heads and long, wispy tails, the sight of a comet in the night sky used to scare people. Now we know that comets are part of our solar system family. They are icy objects made of materials left over after our solar system formed. Scientists want to find out all about comets to help us understand how the solar system formed.

Most comets come from the Kuiper Belt, a region beyond the orbit of Neptune. Sometimes the gravitational pull of a planet flings one of these comets headlong toward the Sun.

Comets have another hangout, the Oort Cloud, a far-far-distant cloud of comets that surrounds the solar system. Sometimes the gravitational pull of a passing star stirs up comets in the Oort Cloud, sending some of them flying toward the inner solar system.

Wherever the comet came from, as it approaches the Sun, the Sun's gravity shapes the comet's path into a lopsided orbit. The comet swings around the Sun, then heads out again far into the solar system. When the comet is in the inner solar system where Earth is, that's when we may see it in our skies.

We can see a comet because it grows a big fuzzy cloud around its nucleus (the solid part) as the Sun heats it up. Some of the ice on the surface starts to boil off, and trapped gases may escape in jets. The solar wind pushes this misty cloud of gas and dust into a long tail. (The solar wind is the windy blast of particles from the Sun.)

NASA has sent several spacecraft to visit comets, and we have already learned a lot about them. A new mission called Rosetta, is now on its way to a comet with the long name of Comet Churyumov-Gerasimenko. Rosetta is a European Space Agency mission with help from NASA. When Rosetta arrives at the comet in 2014, it will orbit the comet's nucleus and drop a lander on it. Neither of these feats has ever been done before!

You can be a part of the Rosetta mission! Get "Comet Quest," the brand new iPhone and iPad action game. Check it out at http://spaceplace.nasa.gov/comet-quest. It's free!

This article was written by Diane K. Fisher and provided courtesy of the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.