[DB 1507 (32,33); OAB 17,18] The claim is that comets that pass close to the Sun (the comets we see) cannot have survived for 4.6 billion years in their present orbits. This is not necessarily true for some comets with very long orbital periods, but generally the point is a valid one. However, this claim is a One-Sided Equation that considers the rate at which comets are destroyed without considering how the comet population is replenished. The population of comets is kept in equilibrium by new comets which are continuously introduced into our solar system from beyond Pluto's orbit. When they are far away from the Sun's deteriorating effects, comets can last indefinitely. Comets that are in orbits which bring them close to the sun have not been in those orbits since the formation of the solar system, rather they were perturbed into a close-encounter trajectory by some larger body (e.g. a planet or star or even another comet). Based upon observed comet orbits, scientists have concluded that they come from two major comet sources: the Kuiper belt, a disk-shaped cloud just beyond the orbit of Neptune; and the Oort cloud, a spherically-shaped cloud that may stretch for as far as 1 light-year from the Sun. One piece of evidence favoring this theory is the fact that comets, unlike everything else in the Solar System, have retrograde orbits just as commonly as they have prograde orbits (See Orbits in the Solar System, above). This is strong evidence that comets are not in their original orbits, that rather their orbital directions were picked up randomly when they were thrown into their present orbits, in keeping with the Oort/Kuiper theory. However, due to their small size, low reflectivity, and great distance from the Sun, these objects are nearly impossible to detect. But since the Oort/Kuiper theory is coherent and explains all of the evidence amply, it alone should be sufficient to dispense with the young-Earth objection concerning comet lifetimes. Recently, however, our telescope technology has improved to the point where we no longer need to rely on theory alone to deal with this objection. Since 1995, over 50 Kuiper belt objects have been discovered, dramatically confirming the Oort/Kuiper theory of comet origins. Kuiper belt observations continue to be an ongoing frontier of Planetary Science.