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In my story, a group of creatures lives on the Moon. I know that microlith striking the Moon is fairly common, to the point that EVA suits are built to compensate for it, but I was planning to have a “meteor shower” kind of deal, where a “rain” of small asteroids or particles hits a small area over a short period (ten minutes or so). This way, the creatures would feel or see the microlith falling at high velocity and be forced to seek shelter, similarly to a very short rainstorm on Earth. Does this really happen at all, or is the impact of micrometeorites more spread out? How frequently would something like this occur?

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  • $\begingroup$ since it would be flying at few km/s I think it's impossible to see it without an atmosphere turning into a bright flash $\endgroup$
    – L.Dutch
    Nov 8, 2021 at 16:23
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    $\begingroup$ "the creatures would feel or see the microlith falling at high velocity and be forced to seek shelter" Those creatures are quite something if they are able to live on a planetary body without atmosphere. Also, they would have quite a good vision if they are able to see small objects traveling at km/s in vacuum. $\endgroup$ Nov 8, 2021 at 16:25
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    $\begingroup$ Don't forget that the micrometeorites might often make visible spashes in the lunar regolith when they hit. I believe that lunar craters go down in size to microscopic sizes. So I presume that the Moon is often struck by tiny micrometeorites the right size to make splashes of dust similar to raindrops splashing in puddles. My answer at scifi.stackexchange.com/questions/87540/… mentions a fictional visible meteor shower on the moon. The question is how far apart the correct size micrometeorites would be in typical showers. $\endgroup$ Nov 8, 2021 at 18:18
  • $\begingroup$ "microlith striking the Moon is fairly common".. unlikely. Microlith is a small flint tool from stoneage. You mean micrometeor, i assume. $\endgroup$
    – PcMan
    Nov 8, 2021 at 18:20

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Direct micrometeors from space would be way,way,way too rare for this.
Impact from something that can be felt, much less something that can be detected ahead of time, would be weeks to many years between single events.

But... how about a strong meteor impact a few (dozen? hundred?) km away. What your astronauts are experiencing is the debris that was kicked up by that impact. This would be both vastly more numerous, and much slower than incoming meteors. It will be both detectable, and yet slow enough for them to have time to seek shelter, with debris travel times of several minutes, and speeds of 1-2km/s only

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  • $\begingroup$ This could work really well. Is there any kind of estimate as to how often this could happen, assuming the meteor was big enough to kick up a potentially dangerous (to a human if reference is needed) amount of debris? $\endgroup$
    – Mark Price
    Nov 8, 2021 at 23:15
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    $\begingroup$ It would require a meteor of about 5m or larger.. Expect to see one such impact on the moon per 5-10 years tops. Possibly a bit less it's very hard to guesstimate the Earth's shielding factor. It will be less common than an natural disaster on Earth. i.e. "happens often enough but very rarely near you" $\endgroup$
    – PcMan
    Nov 9, 2021 at 5:30
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The only plausible way for what you ask to happen, apart from a close impact, is to have the tail of comet cross the lunar orbit.

While producing the tail, the evaporating matter also moves particles away from the comet surface, which then move into space forming the tail. If the tail happens to be intersecting the moon orbit it will end up hitting its surface.

However, the phenomenon will be very rare, and moreover particles traveling at few km/s cannot be seen by the naked eye, even more considering that there is no atmosphere to light them up.

For a reference, look at some of the images taken by Philae and Rosetta during the landing on the comet.

enter image description here

Some of the brightest spot you see are particles leaving the comet surface.

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  • $\begingroup$ Definitely possible. It matches the requirement for micrometeor "rain" very well, but will most certainly not be sudden, unexpected, and short duration so as to be "similarly to a very short rainstorm on Earth." $\endgroup$
    – PcMan
    Nov 9, 2021 at 5:33
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Meteor showers!

We can watch meteor showers on Earth. Most of them burn up in pretty streaks in the sky. Not so on the moon. Every single one plows right into the surface.

https://phys.org/news/2006-12-lunar-leonid.html

Meteoroids that hit Earth disintegrate harmlessly (and beautifully) in the atmosphere. But the Moon has no atmosphere to protect it, so meteoroids don't stop in the sky. They hit the ground. The vast majority of these meteoroids are dust-sized, and their impacts are hardly felt. But bigger debris can gouge a crater in the lunar surface and explode in a flash of heat and light. Some flashes can be seen from Earth.

During the passage through Tempel-Tuttle's debris field, Cooke's team trained their telescopes (two 14-inch reflectors located at the Marshall Space Flight Center) on the dark surface of the Moon. On Nov. 17th, after less than four hours of watching, they video-recorded two impacts: a 9th magnitude flash in Oceanus Procellarum (the Ocean of Storms) and a brighter 8th magnitude flash in the lunar highlands near crater Gauss. "The flashes we saw were caused by Leonid meteoroids 2 to 3 inches (5 to 8 cm) in diameter," says Cooke. "They hit with energies between 0.3 and 0.6 Giga-Joules." In plain language, that's 150 to 300 pounds of TNT.

The Perseid meteors also make impacts on the moon that can be seen from Earth - dozens every year. https://science.nasa.gov/science-news/science-at-nasa/2008/02sep_lunarperseids

For every big explosion one can see from Earth there are many tiny ones that do not kick up enough light and heat to be seen from Earth, but which would definitely make a divot. Even a milligram of rock coming in from space could make your day a bad one. Actually I did the math: 1 mg moving at 50 km/s has the force of a stick of dynamite.

Moon dwellers would definitely pay attention to the periodic meteor showers we know about, and seek cover when they were raining down on the moon.

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    $\begingroup$ Exactly what I was looking for. Would these larger impacts be strong enough to create a lot of shrapnel/debris? That would make a similar effect to what I’m looking for. $\endgroup$
    – Mark Price
    Nov 8, 2021 at 23:18
  • $\begingroup$ 300 pounds of TNT would throw stuff around, I think. All the light from those flashes described is from glowing hot rock - no gas to glow. No shock wave to knock you down. And without air resistance flying shrapnel will go much farther. $\endgroup$
    – Willk
    Nov 8, 2021 at 23:46

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