Is there any scenario where a large impactor striking the far side of the Moon would perturb the Earth's orbit enough to reduce the distance from the Earth to the Sun and still remain within the habitable zone?
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2 Answers
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... and still remain within the habitable zone?
Everything perturbs all the time. Every change in the distribution of mass in the solar system (or in the universe) perturbs the orbit of the Earth... so the literal answer is "yes".
But suppose someone asked instead:
Can an 'invisible' impact perturb the orbit enough to have a measurable effect on the the climate
The answer to that question would be "no" The Earth's orbit already takes it closer and further from the sun each year, reaching its closest in January. To move the Earth enough that it has a climatic effect would require a huge force on the Earth-moon system, and an impact on the far side of the moon that is large enough to cause such a perturbation would cause other effects (like melting the moon, disrupting it completely, blasting enough of the moon into space and having it fall to Earth....) These would affect the climate much more.
An undetected asteroid impact on the far side of the moon might change the orbit of the Earth-moon system around the sun by millimeters.
It is just really really hard to change the orbit of a planet.
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$\begingroup$ The literal answer is "yes", but I'm also answering the implied question. "change the climate while remaining in the habitable zone" $\endgroup$– James KCommented Sep 19, 2020 at 9:23
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1$\begingroup$ I've taken the liberty to make a proposed edit. how does that look? $\endgroup$– uhohCommented Sep 19, 2020 at 9:39
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No.
A short calculation: the Moon orbits the Earth with with 1022m/s. The mass of the Earth is 81 times bigger than of the Moon.
That means, that also the Earth orbits the common center of mass of the Moon-Earth system by $\frac{1022}{81}=12 m/s$.
The largest possible indirect effect of such a Moon impact would be roughly so high, as if the Moon would disappear.
Thus, it is hard to think that it could cause a larger perturbation to the Earth's velocity around the Sun, than 12m/s.
But the Earth is going by 29800m/s around the Sun. A 12m/s change, happens it in any direction, would not be enough to cause any measurable effect to the climate.
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$\begingroup$ Btw, other secondary effects of the impact, like meteor shower, space waste, could be dangerous. $\endgroup$– peterhCommented Sep 19, 2020 at 22:06