Final answer:
Most asteroids are found between Mars and Jupiter, in the asteroid belt. Kirkwood gaps are areas within the asteroid belt with fewer asteroids, caused by Jupiter's gravitational pull creating orbital resonances.
Step-by-step explanation:
Most asteroids lie between the planets, Mars & Jupiter. 'Kirkwood gaps' in the asteroid belt orbits are caused by orbital resonances with the planet Jupiter. The asteroid belt is a vast region where asteroids revolve about the Sun in the same direction as the planets, within a region that has orbital periods ranging between 3.3 to 6 years. Despite the science fiction portrayal of a densely populated asteroid belt, the spacing between these celestial bodies is quite vast, averaging several million kilometers apart.
This spacing has been beneficial for spacecraft like Galileo and Cassini, allowing them to traverse the asteroid belt without encountering collisions. Another impactful aspect caused by the gravitational influence of the giant planet Jupiter are the Kirkwood gaps, which are essentially areas within the belt that are largely clear of asteroids due to orbital resonances. These gaps occur where the orbits of asteroids would have a simple ratio to the orbit of Jupiter, leading to unstable orbits and resulting in a lower density of asteroids or the ejection of asteroids from the belt.