.如果真係有粒十公里大的小行星撞落月球度. Suppose a 10-km asteroid did hit the Moon’s farside at head-on speed of 20 km/sec.
A size of 10-km means 1/347 Moon’s diameter. So the mass of this asteroid is roughly 1/347 x 1/347 x 1/347 = 1/40,000,000 that of the Moon. With the intrusion of this asteroid, the Moon has virtually no change of its total mass.
Now, the Moon is orbiting the Earth at ~1 km/s. Its kinetic energy (1/2 * mass M * velocity square) will be equal to “0.5 M” units.
By similar calculation, the kinetic energy of the asteroid is equal to 1/2 * 1/40,000,000 M * 20 square = 0.000005 M units. Again this shows the Moon has virtually no change of its orbital speed. Even the orbital speed suffers (possibly moving inward towards the Earth by cm order), it just shortens one sidereal month by a very very small amount.
The asteroid impact only creates a new crater (diameter 100~150 km) on the Moon. The Earth has no change, except a chance to capture few debris (lunar meteorites) escaped from the impact ejecta.
But if this asteroid hits the Earth instead of the Moon, abrupt climate changes leads to floodless. Many lives lost including mankind. |
發表於 2007-11-17 10:44:12
辯論測試
發表於 2007-11-18 15:30:49
發表於 2008-1-17 15:48:04
