I’m thinking that Cecil misses an important point when he responds to “I plan to destroy the moon. What effect would this have on the earth?”. Just how you do it is all-important as to what happens next.
If you explode it or use some “simple process of vaporization” (as Cecil puts it), the bulk of what used to be the moon will stay in orbit, and dogs are left howling at that fuzzy white cloud in orbit. Some matter will be blown out of Earth’s orbit (but not out of the solar system), some will rain down on the earth (with lots of fun consequences).
If, on the other hand, you attach a bunch of space-going tugs to the poles to send it off to the Kuiper (sp?) belt, the gravitational pull of the moon (as it stops orbiting and starts moving away) will affect the Earth’s orbit. Not only that, but it will noticably affect the orbits of any planets, moons, and asteroids it passes. Whether or not it’s a big deal depends on a lot of factors.
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If you’re going to hypothesize destroying the Moon, you might as well include removing the debris from the Solar System, putting the Earth in the orbit the Earth-Moon system used to occupy, with the same tilt, and putting back any planets and asteroids you disturbed. This is essentially the situation Cecil answered.
Cecil talked about “vaporization” as a means to keep big chunks of stuff from raining down on the Earth, but he didn’t talk about restoring orbits (!!!).
The point I was making was that if you somehow break up the moon, most of it will still be in orbit, so you don’t change much in terms of orbits. On the other hand, you go dragging it off somewhere, it will affect orbits on the way out, and probably much more that if you were able to somehow teleport it instantaneously.
I think the point of the column was to imagine the earth without the moon, would it still support life, etc. So we just have to assume the moon disappears.
I suspect Cecil underestimates the danger in point 3 of his reply. Seems like I’ve read that the moon acts as a kind of flywheel on the earth, and that without it the earth would “wobble” around its axis much more than it already does. Mars has shown a much greater tendency to wobble, resulting in huge, rapid climate changes(for what passes for a climate on Mars).
Yes, but there are other differences between Earth and Mars besides Mars’s lack of a significant moon. So before we assume Luna is essential to keeping Earth’s axis on the up-and-up, I’d want to know if Venus and Mercury (two other moonless terrestrials) also exhibit this Marsian wobble, or why they don’t.
The “flywheel” hypothesis is attractive (people seem to want to need Luna, to the extent that I wonder if it’s coded in our genome somewhere), but given Luna’s very tiny mass relative to Earth, I’m very skeptical of any claim that chaos would result from its sudden absence.
The Moon may be less massive, but it has most of the angular momentum of the system:
I = angular momentum = Radius * Mass * Velocity
Imoon = 3.8410^5 * 7.3510^25 * 29.78 = 8.41*10^32 km^2 g / s
Iearth < 6378 * 5.9810^27 * 0.464 = 1.7710^31 km^2 g / s
Where for the Earth, I was too lazy to find the correct angular momentum of a sphere, so I just assumed all the mass is at the equator. This is an overestimate, hence the “<”. So the Earth’s rotation has less than about 1/50th the angular momentum of the Moon.
As far as looking at Venus and Mercury, Mercury’s rotation is synchronized with its orbit, so it may not help settle the matter. Looking at Venus may help, but it rotates very slowly, so you’d have to take that into account, somehow. I don’t know what effect that would have on the comparison.
I’m not saying the “flywheel” hypothesis is valid, however.
Don’t forget how unusually large the moon is for a satellite. Some astronomers almost consider the earth and moon to be co-planets. But granted it’s mass is pretty insignificant compared with earth’s.
What I’m saying is that removing the moon is not a simple mass reduction problem as stated in #3 of Cecil’s column. The moon produces torque on the earth, and is in turn being slowly raised into a higher orbit.
What would happen to the earth if this gravitatonal force were suddenly removed? The tides, for instance – the oceans bulge out on the side of the earth facing the moon (and to a lesser extent on the side opposite). Normally this bulge slowly rotates around the earth in concert with the moon. But now the moon is suddenly gone. Wouldn’t tidal waves be one result? Not the end of life as we know it, but pretty catastrophic for anyone with oceanfront property. (Maybe I’ve found a solution to the election mess in FL?)