6 ms·

The moon’s permanent shadows are coming to light

62 points by theafh 4y ago

PaulHoule 4y ago
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.)
- Melatonic 4y ago
  Aren't there also huge lava tubes on the moon? I wonder if there could be water trapped somewhere down there (or other volatiles)
  - ncmncm 4y ago
    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.
verisimi 4y ago
"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.
- sam-s 4y ago
  at that speed, the angle does not matter, the crater will be circular because the impact vaporized the rocket.
  - Teever 4y ago
    I don't follow. Can you elaborate?
    - JaimeThompson 4y ago
      "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-craters-al/ https://www.scientificamerican.com/article/why-are-impact-cr...
  - ncmncm 4y ago
    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.
    - gshubert17 4y ago
      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/20090043092.pdf 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.
swamp40 4y ago
> "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?
- sreevisakh 4y ago
  Gases escape if their molecular velocity exceeds the escape velocity of the planetary body. That's why smaller and hotter objects lack an atmosphere.
- usefulcat 4y ago
  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.
  - jkqwzsoo 4y ago
    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.
    - Arnavion 4y ago
ncmncm 4y ago
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.
- go_elmo 4y ago
  then again further cooling 20 °C in a vacuum and complete darkness might also be feasible
  - ncmncm 4y ago
    You could maybe have a liquid nitrogen hose bonded to the tape, circulating to a refrigeration unit on the rim.
  - tomrod 4y ago
    Vacuum is not a good conductor of heat, unfortunately. Air would be.
    - Darkphibre 4y ago
      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_141.v2.pdf?sequence=1 https://ttu-ir.tdl.org/bitstream/handle/2346/67554/ICES_2016...
    - m4rtink 4y ago
      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.
  - ncmncm 4y ago
    It is possible a mirrored tent over it would keep enough glare from sunshine on the rim off, allowing it to cool further.
marcodiego 4y ago
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?
- layer8 4y ago
  There are plans for data centers on the moon: https://spacenews.com/lonestar-emerges-from-stealth-with-plans-for-lunar-data-centers/ https://spacenews.com/lonestar-emerges-from-stealth-with-pla...
tectonic 4y ago
Moon Monday is a great newsletter for keeping up with lunar science and exploration: https://blog.jatan.space/s/moon-monday/archive https://blog.jatan.space/s/moon-monday/archive

62 points by theafh 4y ago

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.)

Melatonic 4y ago
Aren't there also huge lava tubes on the moon? I wonder if there could be water trapped somewhere down there (or other volatiles)
- ncmncm 4y ago
  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.

verisimi 4y ago

"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.

sam-s 4y ago
at that speed, the angle does not matter, the crater will be circular because the impact vaporized the rocket.
- Teever 4y ago
  I don't follow. Can you elaborate?
  - JaimeThompson 4y ago
    "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-craters-al/ https://www.scientificamerican.com/article/why-are-impact-cr...
- ncmncm 4y ago
  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.
  - gshubert17 4y ago
    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/20090043092.pdf 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.

swamp40 4y ago

> "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?

sreevisakh 4y ago
Gases escape if their molecular velocity exceeds the escape velocity of the planetary body. That's why smaller and hotter objects lack an atmosphere.
usefulcat 4y ago
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.
- jkqwzsoo 4y ago
  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.
  - Arnavion 4y ago

ncmncm 4y ago

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.

go_elmo 4y ago
then again further cooling 20 °C in a vacuum and complete darkness might also be feasible
- ncmncm 4y ago
  You could maybe have a liquid nitrogen hose bonded to the tape, circulating to a refrigeration unit on the rim.
- tomrod 4y ago
  Vacuum is not a good conductor of heat, unfortunately. Air would be.
  - Darkphibre 4y ago
    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_141.v2.pdf?sequence=1 https://ttu-ir.tdl.org/bitstream/handle/2346/67554/ICES_2016...
  - m4rtink 4y ago
    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.
- ncmncm 4y ago
  It is possible a mirrored tent over it would keep enough glare from sunshine on the rim off, allowing it to cool further.

marcodiego 4y ago

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?

layer8 4y ago
There are plans for data centers on the moon: https://spacenews.com/lonestar-emerges-from-stealth-with-plans-for-lunar-data-centers/ https://spacenews.com/lonestar-emerges-from-stealth-with-pla...

tectonic 4y ago

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