5 ms·

Lunar Lava Tube

ncmncm 5y ago
If ever there were something that needs exploring, it is lunar lava tubes. They must be millions, maybe tens or hundreds of millions of years old. Probably crystals have been growing in them the whole time. The robot sent to explore it should look like a kangaroo.
- ajuc 5y ago
  I think crystals need the required substance to be liquid to grow? If you just put salt grains near each other you don't get a crystal, you need to dissolve it in water or to melt it.
  - ncmncm 5y ago
    With enough time, sublimation and vapor deposition can do the job, under the right conditions. If you come in after the experiment has been running for a hundred million years, there are probably surprises in store, things no one has ever seen.
    - BurningFrog 5y ago
      I know nothing, but my physics instincts say any vapor that might form crystals would evaporated in the eternal vacuum.
      - nitrogen 5y ago
        Vacuum deposition is a thing.
        Tagbert 5y ago
        Yes, but the result is usually a more granular, friable substance rather than a cohesive crystal.
        ncmncm 5y ago
        Have you heard of "molecular beam epitaxy"? You can make functional microelectronics with vacuum vapor deposition.
      - ncmncm 5y ago
        This is the same argument as saying since all the stuff that might be deposited on (say) a gypsum crystal can dissolve in water, the water would carry it all away and there would be no gypsum crystals. But we do, in fact, get gypsum crystals: http://i0.wp.com/unusualplaces.org/wp-content/uploads/2016/07/1200px-Cristales_cueva_de_Naica.jpg http://i0.wp.com/unusualplaces.org/wp-content/uploads/2016/0... A likely process would be a (maybe impure) deposit of a mineral at one end of a tunnel, with a heat source, whether the sun through a skylight or thinner roof, or a geologic hot spot, causing the mineral to sublimate, howsoever slowly, and some of the vapor migrating to a colder part of the tunnel, and crystalizing out there.
- xattt 5y ago
  Or is this the problem the Boston Dynamics robots were looking to solve?
- zabzonk 5y ago
  > The robot sent to explore it should look like a kangaroo What, sort of furry, beige colour, big feet, long tail, and a goofy looking offspring peering out from a pouch? I fail to see how this will aid lunar exploration :)
  - ncmncm 5y ago
    Who said anything about aiding exploration? Some of us want space probes that look like kangaroos. Why should a space probe look like not-a-kangaroo? But anyway a cave is likely to have a floor far too uneven for wheels. Another plausible configuration would be a crab or daddy-long-legs. Operating in the dark, a plutonium RTG radiating heat would seem to threaten to damage the contents of the cave we came to look at. Maybe it sets out solar panels, and reels out a wire as it goes into the dark. And perforce sleeps for two weeks out of each month.
johnwalkr 5y ago
Hey, I've been working on missions and rovers to investigate these for 10 years now. That particular pit at the top of the wikipedia article shown is really convincing, when checked at different times and angles [1]. You can see at some point, the shadow of the crater stops moving with time, this can only be explained by an overhang, which implies a tube is there. As mentioned in the article, these are really attractive from a scientific view, and also could provide much protection from the harsh lunar environment (radiation, 100C + at lunar noon, and -150C during 2 weeks of lunar night). https://www.researchgate.net/figure/Mare-Tranquillitatis-pit-A-near-nadir-image-M126710873R-and-B-7-emission-angle_fig4_234129963 https://www.researchgate.net/figure/Mare-Tranquillitatis-pit...
- sandworm101 5y ago
  >> could provide much protection from the harsh lunar environment Or introduce a host of new threats. Without the minimal "erosion" of micrometeoroids and dust, I would expect every edge on every rock in such tubes to be sharp. And the lack of tectonic activity/wind/water means that any 3d rock structure might well be on the edge of collapse. I wouldn't attempt to walk down one of these tunnels.
  - tokai 5y ago
    >I would expect every edge on every rock in such tubes to be sharp Why? The rock has been melted away, if anything things should be quite smooth in the tubes.
    - andrewflnr 5y ago
      Having walked in a couple lava tubes, "smooth" is not really the word I would use, but I suppose neither is "sharp". (Among other things, imagine popcorn ceiling texture, on the floor, made of rock)
  - me_me_me 5y ago
    I think you just described precisely why some people would love to explore those kind of formations.
denton-scratch 5y ago
It has always struck me that in pictures of the moon's surface, what are supposed to be depressions usually look like bumps instead. I'm not referring to the photo at the top of the article; that definitely looks like a hole. But the next one down, under "Observational Evidence", is an example. I find it very difficult to adjust my gaze so they look like pits rather than bumps. I watched the Apollo moon-landing on TV as a kid; even when they were flying in, a few hundred feet over the surface, I couldn't make the craters look like craters, even though I knew they were craters. It feels like I have some kind of cognitive deficiency.
- orbital-decay 5y ago
  It's not just you. Terrain reversal is also a problem in cartography; that's why hillshades are usually lit from the NW direction. (although there are other solutions to this issue)
- ncmncm 5y ago
  It takes practice, but it can be overcome. With enough practice, you can flip them convex and concave and back, at will. In the meantime, flipping the image over, top to bottom, often helps.

If ever there were something that needs exploring, it is lunar lava tubes. They must be millions, maybe tens or hundreds of millions of years old. Probably crystals have been growing in them the whole time. The robot sent to explore it should look like a kangaroo.

ajuc 5y ago
I think crystals need the required substance to be liquid to grow? If you just put salt grains near each other you don't get a crystal, you need to dissolve it in water or to melt it.
- ncmncm 5y ago
  With enough time, sublimation and vapor deposition can do the job, under the right conditions. If you come in after the experiment has been running for a hundred million years, there are probably surprises in store, things no one has ever seen.
  - BurningFrog 5y ago
    I know nothing, but my physics instincts say any vapor that might form crystals would evaporated in the eternal vacuum.
    - nitrogen 5y ago
      Vacuum deposition is a thing.
      - Tagbert 5y ago
        Yes, but the result is usually a more granular, friable substance rather than a cohesive crystal.
        ncmncm 5y ago
        Have you heard of "molecular beam epitaxy"? You can make functional microelectronics with vacuum vapor deposition.
    - ncmncm 5y ago
      This is the same argument as saying since all the stuff that might be deposited on (say) a gypsum crystal can dissolve in water, the water would carry it all away and there would be no gypsum crystals. But we do, in fact, get gypsum crystals: http://i0.wp.com/unusualplaces.org/wp-content/uploads/2016/07/1200px-Cristales_cueva_de_Naica.jpg http://i0.wp.com/unusualplaces.org/wp-content/uploads/2016/0... A likely process would be a (maybe impure) deposit of a mineral at one end of a tunnel, with a heat source, whether the sun through a skylight or thinner roof, or a geologic hot spot, causing the mineral to sublimate, howsoever slowly, and some of the vapor migrating to a colder part of the tunnel, and crystalizing out there.
xattt 5y ago
Or is this the problem the Boston Dynamics robots were looking to solve?
zabzonk 5y ago
> The robot sent to explore it should look like a kangaroo What, sort of furry, beige colour, big feet, long tail, and a goofy looking offspring peering out from a pouch? I fail to see how this will aid lunar exploration :)
- ncmncm 5y ago
  Who said anything about aiding exploration? Some of us want space probes that look like kangaroos. Why should a space probe look like not-a-kangaroo? But anyway a cave is likely to have a floor far too uneven for wheels. Another plausible configuration would be a crab or daddy-long-legs. Operating in the dark, a plutonium RTG radiating heat would seem to threaten to damage the contents of the cave we came to look at. Maybe it sets out solar panels, and reels out a wire as it goes into the dark. And perforce sleeps for two weeks out of each month.

johnwalkr 5y ago

Hey, I've been working on missions and rovers to investigate these for 10 years now. That particular pit at the top of the wikipedia article shown is really convincing, when checked at different times and angles [1]. You can see at some point, the shadow of the crater stops moving with time, this can only be explained by an overhang, which implies a tube is there. As mentioned in the article, these are really attractive from a scientific view, and also could provide much protection from the harsh lunar environment (radiation, 100C + at lunar noon, and -150C during 2 weeks of lunar night). https://www.researchgate.net/figure/Mare-Tranquillitatis-pit-A-near-nadir-image-M126710873R-and-B-7-emission-angle_fig4_234129963 https://www.researchgate.net/figure/Mare-Tranquillitatis-pit...

sandworm101 5y ago
>> could provide much protection from the harsh lunar environment Or introduce a host of new threats. Without the minimal "erosion" of micrometeoroids and dust, I would expect every edge on every rock in such tubes to be sharp. And the lack of tectonic activity/wind/water means that any 3d rock structure might well be on the edge of collapse. I wouldn't attempt to walk down one of these tunnels.
- tokai 5y ago
  >I would expect every edge on every rock in such tubes to be sharp Why? The rock has been melted away, if anything things should be quite smooth in the tubes.
  - andrewflnr 5y ago
    Having walked in a couple lava tubes, "smooth" is not really the word I would use, but I suppose neither is "sharp". (Among other things, imagine popcorn ceiling texture, on the floor, made of rock)
- me_me_me 5y ago
  I think you just described precisely why some people would love to explore those kind of formations.

denton-scratch 5y ago

It has always struck me that in pictures of the moon's surface, what are supposed to be depressions usually look like bumps instead. I'm not referring to the photo at the top of the article; that definitely looks like a hole. But the next one down, under "Observational Evidence", is an example. I find it very difficult to adjust my gaze so they look like pits rather than bumps. I watched the Apollo moon-landing on TV as a kid; even when they were flying in, a few hundred feet over the surface, I couldn't make the craters look like craters, even though I knew they were craters. It feels like I have some kind of cognitive deficiency.

orbital-decay 5y ago
It's not just you. Terrain reversal is also a problem in cartography; that's why hillshades are usually lit from the NW direction. (although there are other solutions to this issue)
ncmncm 5y ago
It takes practice, but it can be overcome. With enough practice, you can flip them convex and concave and back, at will. In the meantime, flipping the image over, top to bottom, often helps.