Comets have the further feature that they carry a disproportionate amount of energy compared to asteroids, since they are generally moving at faster speeds—up to 70 or more km/sec as opposed to 10 to 30 km/sec for asteroids. Typically, a ballistic missile travels at less than 11 km/sec, an asteroid at about 20 km/sec, a short-period comet at more like 35 km/sec, and a long-period comet at 55 km/sec, though faster speeds occur too. (See Figure 32.) Kinetic energy grows not only with mass, but also with the square of the velocity. Comets’ greater speeds mean that even less frequent comet
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