[HN Gopher] The moon's permanent shadows are coming to light
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The moon's permanent shadows are coming to light
Author : theafh
Score : 53 points
Date : 2022-04-28 13:45 UTC (9 hours ago)
(HTM) web link (www.quantamagazine.org)
(TXT) w3m dump (www.quantamagazine.org)
| tectonic wrote:
| Moon Monday is a great newsletter for keeping up with lunar
| science and exploration: https://blog.jatan.space/s/moon-
| monday/archive
| marcodiego wrote:
| 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?
| verisimi wrote:
| "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 wrote:
| at that speed, the angle does not matter, the crater will be
| circular because the impact vaporized the rocket.
| Teever wrote:
| I don't follow. Can you elaborate?
| JaimeThompson wrote:
| "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...
| ncmncm wrote:
| 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 wrote:
| 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/2009004
| 3092/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.
| ncmncm wrote:
| 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.
| gshubert17 wrote:
| 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.
| ncmncm wrote:
| 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 wrote:
| then again further cooling 20 degC in a vacuum and complete
| darkness might also be feasible
| ncmncm wrote:
| You could maybe have a liquid nitrogen hose bonded to the
| tape, circulating to a refrigeration unit on the rim.
| tomrod wrote:
| Vacuum is not a good conductor of heat, unfortunately. Air
| would be.
| Darkphibre wrote:
| 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...
| m4rtink wrote:
| 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.
| PaulHoule wrote:
| 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 wrote:
| 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 wrote:
| 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.
| swamp40 wrote:
| > "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?
| usefulcat wrote:
| 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 wrote:
| 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.
| sreevisakh wrote:
| Gases escape if their molecular velocity exceeds the escape
| velocity of the planetary body. That's why smaller and hotter
| objects lack an atmosphere.
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