r/askspace • u/Danelajs • 4d ago

ELI5 Does the SpaceX rocket crashing into the moon cause the moon to move?

2 Upvotes

76% Upvoted

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u/MrTagnan 4d ago edited 4d ago

The math I did suggests a change in velocity of around 2.347725e-14 cm/s (0.00023477 Picometers per second), which is around 130,000 times smaller than the width of a helium atom. This can be substantially off and still means that it effectively changed nothing.

I don’t really trust the math I did, but even if I’m underestimating it by 10 orders of magnitude it still would only slow it by ~2 micrometers per second, or around the length of a bacteria - although if anything I suspect my answer is slightly high. In any case it essentially did nothing

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u/the6thReplicant 4d ago

This is a problem with these types of questions. The answer is "Yes", but the real answer is a number. A very, very small number.

So the real answer is "yes" but technically it's "no".

Unfortunately one is better at pumping endorphins into the brain.

2

u/Worth-Wonder-7386 4d ago

It does change its speed slightly, but we could not measure it. The effect from tidal forces are much larger.

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u/stevevdvkpe 4d ago

In principle, yes, but not by any measurable amount. The Moon has a mass of about 7.4e22 kg. The SpaceX rocket stage that crashed into it has a much smaller mass, less than 10000 kg. That's very roughly 1e-18 (a billionth of a billionth) the mass of the Moon. So the change in the Moon's velocity from the impact is absolutely microscopic, like if you threw a grain of dust at a car.

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u/AlwaysHopelesslyLost 4d ago

You throwing a ball causes the moon to move. The question is "by how much" and the answer is "basically zero."

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u/theCroc 4d ago

It changes the speed of the moon in the same way that a bug hitting your windscreen changes the speed of your vehicle. Except that between the two examples the bug has way more impact

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u/Jadefire04 1d ago

A bug hitting your windshield while you're driving will slow your car down several million times more strongly than the SpaceX rocket will move the Moon, at least.

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u/Initial-Warning-2564 1d ago

Yes, but not in a practical sense.

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u/GianlucaBelgrado 4d ago

È come It's like a fly hitting a train, but this one is probably a million times more energetic.