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Comment by kseverest | Hacker News Reader

I wonder how stable such tubes would be? No water erosion, no earthquakes, even though they must have formed at a time that was more geologically active. They could be on the edge of collapse if say, a large vehicle drove in them. Am I wrong?

Just a first thought. Other than that, they could probably serve as a goal for human spaceflight, an intermediate step between walking on the moon and colonizing mars.

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The article mentions the use of inflatable housing inside. Seems like a wise move given we have so little experience with their stability.

If they've survived this long, then presumably they are very unlikely to collapse on their own. That is, settlers would only need to worry about collapse cause by their own movements.

The odds of them being 'on the verge of collapse' are relatively low in my thinking. Unless there is some process that takes them to the edge and then stops that we don't understand. Otherwise, they are likely to have either already collapsed or be somewhat stable.

The moon is pretty dead, so no processes exist... if they’re stable, barring asteroid strike. They’d remain stable. The problem is metastability, the “death block” problem in ice climbing.

There are moonquakes so not completely dead. https://www.nasa.gov/exploration/home/15mar_moonquakes.html

Wouldn’t the acceleration of falling objects be slow enough that the force delivered be much lessened?

I'd imagine the tubes are relatively stable because they regularly (at geologic time scales) experience seismic disturbances from weak plate tectonic activity and especially impact events.

> no earthquakes No but how about moon-quakes? Ok, not geologically active you say. But moon's been bombarded by asteroids it's surface is full of craters. Creating a crater wouldn't that be an equivalent of a moon-quake?

You are absolutely correct.

This is the correct answer. These lava tubes are, at their youngest, a couple billion years old. Since then, the moon has been thwacked very hard and -- on those timescales -- often. If the tubes haven't collapsed yet, then there's a high likelihood that they're exceptionally stable.

That could be survivor bias. Maybe there used to be a lot more of them.

Wouldn't a collapsed tube be very distinctive visually?

Very much so -- and one has even been explored by humans!

https://en.wikipedia.org/wiki/Hadley%E2%80%93Apennine

Yes survivor bias. But since these survived, they are likely to be structurally sound. Like antique furniture or structures on Earth.

Does that count as natural selection?

I don't think lava tubes breed.

Survival of the fittest, then.

You're not accounting for tidal forces. The same forces that create the tides on Earth also affect the moon. In this case via moon-quakes.

https://phys.org/news/2017-08-moon-tidal-stress-responsible-...

But the moon is one-face, so tidal stress should be constant.

What about the sun's? If the force is strong enough to make earth orbit, and moon-to-sun distance oscillates, plus seasonal behaviour, there must be quite some straining tides...

oh yeah, that makes sense. It's a tiny fraction of the moon-sun distance, but it would have some efrect. Is it a "tidal" force, though?

The sun also creates the tides.

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