|MadSci Network: Physics|
Dove - you are right that spaceships and satellites take a small amount of matter away from the surface of the Earth. But this amount is very, very small. For example, consider a 2 metric-ton satellite, which has a mass of 2000 kg. The Earth's mass is 6x10^24 kg, so the satellite has only 3x10^(-25), or 0.0000000000000000000000003 times the mass of the Earth. Pretty small, so even a million satellites will not have much effect. The Earth also gains mass when meteorites fall to the ground from space. I don't know how big the total mass gain is, but it might even be enough to balance mass loss due to satellites. The Earth's orbit will change in time, but this will be due more to gravitational perturbations from the other planets, and slight changes in the mass of the Sun as it ages. I don't know if rocket exhaust, for example, causes chemical changes in the atmosphere; it might be interesting to try and find out about this on the Web. Pauline
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