And, unlike the sun, stars, and moon, comets did not seem to appear on any schedule. Comets were a deep mystery. We now know that comets are part of our solar system. Like the planets, they orbit the sun. Some comets, called short-period comets, take up to 200 years to make one orbit.
Comets are the icy leftovers from when our solar system formed.
We can learn much about how the solar system began by studying comets. We have taken wonderful pictures of comets, but we have never before landed on one. We don't yet know. We do know that when the spacecraft arrives, it will have a very exciting time carrying out its assignments. It may be soft, like cotton candy, or hard like a rock.