Let's tackle gravity first. Every object in the solar system experiences a gravitational pull from the sun; the farther away one is from the sun, the weaker the pull. Provided, however, that the sun's gravity is still stronger at your position in space than the gravity from any other stars, then your motion through space will be subject to an acceleration which pulls you towards the sun.

At this point, it is useful to introduce a more convenient unit of measurement for distance: the astronomical unit (AU). A distance of 1 AU is the distance between the sun and Earth, which is approximately 150 million km. All of the known planets, asteroids, and almost all of the known comets are gravitationally bound to the sun and orbit around it. More distant objects experiencing a weaker gravitational pull, take longer to complete an orbit.

The Earth, at 1 AU of course, takes one year. Jupiter, orbiting the sun at 5 AU, takes just under 12 years. Distant Pluto (about 40 AU) takes 248 years—so long in fact, that it hasn't even completed one orbit of the sun since it was discovered in 1930. Pluto, however, is far from being at the edge of the solar system; there are many more distant worlds.

The most distant gravitationally bound objects to the sun are aperiodic comets. Aperiodic, or long-period comets, can take many thousands of years to complete one solar orbit. All of them have completed no more than a single passage through the inner solar system during recorded history.