The moon’s permanent shadows are coming to light | Hacker News Reader

The moon’s permanent shadows are coming to light

quantamagazine.org

62 pointstheafh26 comments

Temperatures are permanently below freezing almost everywhere on the moon if you dig a few meters into the regolith. If you buried some ice underground it would stay there for a while but if you don't wrap it up in a vapor barrier it would eventually sublimate and disappear.

If there was a geological structure that trapped the water vapor (like the trapping structures in oil and gas deposits on Earth) and maintained some vapor pressure there could be deposits of water ice anywhere on the moon.

It would be really cool if the permanently shadowed areas had large amounts of nitrogen and carbon oxide ice because that would provide most of the volatiles to support technology and civlization on Luna.

(Without that, lunar water is less transformative than you think. There is a certain ratio of nitrogen/hydrogen and carbon/hydrogen you need to do industry and you're still limited by the need to ship up whatever isn't available on Luna. Similarly as a rocket fuel hydrogen from Luna competes with hydrogen from Earth and with Starship-grade rockets Earth hydrogen is pretty competitive.)

Aren't there also huge lava tubes on the moon? I wonder if there could be water trapped somewhere down there (or other volatiles)

The interiors of these lava tubes will have stuff seen nowhere else in the solar system. They are millions, even hundreds of millions of years old, so evidence of processes that take that long will be everywhere inside. Picture stuff sublimating and crystallizing just a few atoms at a time, building up fantastic filigree.

It probably needs a probe modeled on an ostrich or kiwi to explore inside, moving about by hopping. You would not want anything that makes heat to be on the probe, or it would ruin things when it got close. Even bright light could destroy the best things.

It seems unfortunate that the interior of Shackleton crater is just very slightly too warm for a "high-temperature superconductor" tape to work. To work well, you would want it another 20 degrees colder.

Equipment in the crater could be powered at all times by solar panels stood up on the rim.

then again further cooling 20 °C in a vacuum and complete darkness might also be feasible

You could maybe have a liquid nitrogen hose bonded to the tape, circulating to a refrigeration unit on the rim.

Vacuum is not a good conductor of heat, unfortunately. Air would be.

I mean, the James Webb makes use of such to drop to, what, 20 Kelvin? https://ttu-ir.tdl.org/bitstream/handle/2346/67554/ICES_2016...

Still the thing you manage to cool down (via radiation in the end, of course) will stay cold as it won't pick up more heat from the environment so easily in vacuum.

It is possible a mirrored tent over it would keep enough glare from sunshine on the rim off, allowing it to cool further.

Moon Monday is a great newsletter for keeping up with lunar science and exploration: https://blog.jatan.space/s/moon-monday/archive

How about building solar plants on peaks of eternal light on the Moon? You'd have cheap electricity for a colony and, hopefully, water. What else is required?

There are plans for data centers on the moon: https://spacenews.com/lonestar-emerges-from-stealth-with-pla...

"On October 9, 2009, a two-ton rocket smashed into the moon traveling at 9,000 kilometers per hour. As it exploded in a shower of dust and heated the lunar surface to hundreds of degrees, the jet-black crater into which it plummeted, called Cabeus, briefly filled with light for the first time in billions of years."

Presumably the rocket also came down at 90 degrees to the lunar surface, making another perfectly circular crater.

at that speed, the angle does not matter, the crater will be circular because the impact vaporized the rocket.

I don't follow. Can you elaborate?

"Why are impact craters always round? Most incoming objects must strike at some angle from vertical, so why don't the majority of impact sites have elongated, teardrop shapes?"

https://www.scientificamerican.com/article/why-are-impact-cr...

9000 km/h is not fast enough to vaporize much rocket.

You can experiment tossing stuff into a tub of talcum powder: craters just really like to be circular, shape of object or angle of impact notwithstanding.

The kinetic energy of 2000 kg at 2500 m/sec is about 6 trillion joules. A ton of TNT is about 4 trillion joules. So the kinetic energy of impact would be the same as 1.5 tons of TNT.

A Nasa document https://ntrs.nasa.gov/api/citations/20090043092/downloads/20... has a slide on the second page about this mission. It estimated about 200 tons of lunar rock and soil were excavated, and that the crater made was about 20-25 meters across and 3 meters deep.

1.5t of TNT certainly has enough energy to vaporize 1.5t of TNT. And, as they say, "then some".

2000 kg of aluminum costs, what, 1/4 billion joules to vaporize? I get 6.25 billion joules of impact energy, not trillion, but still plenty. I am corrected.

You can move a fair bit of material out of the way with that many joules. I guess you would start by vaporizing the 2t of Al plus another several tons of rock, and then dissipate the heat by lofting stuff out of the way as it expands, recycling the heat energy back to kinetic as it cools.

You're right. s/trillion/billion/. The key fact is that the two ton object had the impact of 1.5 tons of TNT. Thanks.

> "The moon isn’t an obvious reservoir of water. “It’s really weird when you stop to think about it,” said Mark Robinson, a planetary scientist at Arizona State University. Its lack of atmosphere and extreme temperatures should cause any water to almost instantly evaporate."

Wouldn't the water vapor get pulled back to the moon via gravity?

Gases escape if their molecular velocity exceeds the escape velocity of the planetary body. That's why smaller and hotter objects lack an atmosphere.

    hydrogen = 1 (atomic weight)
    carbon   = 6
    oxygen   = 8

    H2O = 10
    O2  = 16
    CO2 = 22

Since the moon's gravity is too weak to hold the (heavier) latter two, I conclude that it must also be too weak to hold water molecules, which are lighter still.

Umm, not quite.

H = 1

C = 12 (6 protons, 6 neutrons)

O = 16 (8 protons, 8 neutrons)

H2O = 18

O2 = 32

CO2 = 44

Also, the connection between atmosphere retention and gravity isn't quite so direct. If you positioned a molecule of H2O (or even H2) directly above the surface of the moon with no net velocity, it will fall to the ground. However, once it hit the ground, it would thermalize with the surface and could be ejected in any direction at a range of speeds (or react with the surface and never leave).

The simple/approximate method to compute the stability of the atmosphere is to compute the escape velocity for the body and the Maxwell-Boltzmann distribution of speeds for the gas (which does not depend on gravity). You then integrate the probability distribution P(v) (probability of velocity v) for speeds greater than the escape velocity to infinity. This might result in a case where all gases eventually make their way away from the body, but heavier gases simply take longer.

Not to mention, the gravitational acceleration felt by a body is independent of its mass, so the atomic weight of the gas molecules makes no difference to the acceleration they experience anyway.

The reason "lighter" gases float above "heavier" gases under gravity is not because of different gravitational acceleration but because of buoyancy.

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