The Oort cloud is an immense spherical cloud surrounding the planetary system and extending approximately 3
light years, about 30 trillion kilometres from the Sun. This vast distance is considered the edge of the Sun's orb of physical, gravitational, or dynamical influence. Within the cloud, comets
are typically tens of millions of kilometres apart. They are weakly bound to the sun, and passing stars and other forces can readily change their orbits, sending them into the inner solar system or out to interstellar space. This is especially true of comets on the outer edges of the Oort cloud. The structure of the cloud is believed to consist of a relatively dense core that lies near the ecliptic plane and gradually replenishes the outer boundaries, creating a steady state. One sixth of an estimated six trillion icy objects or comets are in the outer region with the remainder in the relatively dense core.
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