When an asteroid or comet impacts the Earth, the energy released
mainly depends on the mass and velocity of the impactor.
Mass is determined by the volume and density of the object. Below
is a table of some information known about several of the largest
asteroids.
1 Ceres |
2.05 ± 0.05 |
466 |
2 Pallas |
4.2 ± 0.3 |
261 |
4 Vesta |
4.3 ± 0.3 |
262.5 |
16 Psyche |
1.8 ± 0.6 |
132 |
243 Ida |
2.7 ± 0.4* |
58 x 23 |
253 Mathilde |
1.3 ± 0.2 |
28.5 x 25 |
433 Eros |
2.67 ± 0.03 |
17.5 x 6.5 |
For comparison, the density of water is 1 g/cc, rock about 2 g/cc,
and iron about 7 g/cc.
For velocity of an object at impact, consider that the Earth's
escape velocity is 11 km/sec. An object falling toward the Earth
from a large distance (well beyond the moon) and starting from rest
would be moving at close to this velocity on impact. Also, the Earth
is moving at about 30 km/sec in its orbit about the sun; an object
moving in the opposite direction might impact at more than twice
this velocity. Try investigating the other components of the Earth's
velocity through space.
Some current information about actual threats to the Earth can
be found here: NASA/JPL
Near-Earth Object Program
Copyright © 2004, Stephen R. Schmitt
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