A newly discovered moon tunnel • Hacker News Board

Re: A newly discovered moon tunnel

#131

Post by paulvs » Mon, Oct 23, 2017, 2:49 AM UTC

kobeya wrote: post #43

raldi wrote: post #41

Earlier quoted context omitted.

Oddly, the satellite that did the mapping ended its mission in 2009: https://en.wikipedia.org/wiki/SELENE Did it really take until now to analyze its data?

As someone whose job was once to work with that data, yes. It’s a tremendous amount of data and the resources allocated is often a half dozen grad students with a copy of MATLAB. The big iron is only really applied to create the official maps for the planetary science data archives, then real analysis is often paid for piecemeal with relatively small grants.

You worked on this actual data? It's amazing how Hacker News brings together people from such diverse backgrounds.

Re: A newly discovered moon tunnel

#132

Post by kobeya » Mon, Oct 23, 2017, 2:50 AM UTC

DougWebb wrote: post #73

ealloc wrote: post #65

Earlier quoted context omitted.

The reason water exists on earth, and not on mars, may be that life on earth saved the water by discovering photosynthesis. The discovery of photosynthesis caused the "great oxygenation event" which pumped oxygen into the atmosphere. Oxygen reacts with atmospheric hydrogen to form water. Without the oxygen, the very light hydrogen molecules would float to the top of the atmosphere and are easily blown away by solar w…

That seems like it must be incorrect. Life on earth evolved in the oceans, so the oceans had to exist for eons before life evolved and the eons it took for life to evolve photosynthesis and produce significant amounts of oxygen in the atmosphere. If what you're saying is correct, then the earth either started out with much more water than it has now, or the hydrogen escaped a lot more slowly than I'd expect it to.

I've been in planetary science and never encountered this theory. I have a default position of skepticism towards it for that reason, but I don't have a reason to object on the face of it. The question is not where the oceans came from (that's settled -- it came out of the mantle as the Earth cooled, and ultimately before that from cometary impact), but how the oceans did not boil or evaporate off like they did everywhere else. I could understand a theory that they were kept from boiling by being in the habitable zone AND by some combination of life processes, and that this hydrogen-capture mechanism helped replenish the ocean as hydrogen escaped from natural gas upwellings. But I have no sense of the scales and magnitudes involved to see if inputs approximately match outputs without seeing the underlying paper.

Re: A newly discovered moon tunnel

#133

Post by interfixus » Mon, Oct 23, 2017, 2:51 AM UTC

> It might even contain ice or water

As a boy in the early seventies, reading Tintin: Destination Moon, I was always put off by the episode with the underground cave full of slippery ice. That was clearly an outdated view of lunar conditions, which somewhat dented my suspense of disbelief.

Maybe I needn't have worried.

Re: A newly discovered moon tunnel

#134

Post by kobeya » Mon, Oct 23, 2017, 3:13 AM UTC

pjungwir wrote: post #67

JumpCrisscross wrote: post #61

Earlier quoted context omitted.

> Where did the comets get the water they impacted on earth? Hydrogen comes from primordial nucleosynthesis [1] and makes up most of the interstellar medium [2]. Oxygen is produced when neutron stars collide and stars explode [3] as well as when some stars burn [4]. These freely combined in the gas disk from which our solar system formed, condensing into planets, moons, comets and other things [5]. [1] https://en.m.w…

Thank you for this answer! But then why does the water have to come from comets? Why couldn't the Earth have formed with its own water? Also, we seem to have a lot of water. It's really all from comets, a little here, a little there?

There is a "frost line" in the middle of the asteroid belt where you see rocky objects closer and icy objects further. The reason is that closer the Sun has enough energy to sublimate the icy objects into a comet with a tail, where the tail is the icy material being blown off into space. Over billions of years that results in objects with ice-free rocky surfaces inside the frost line, and big, gaseous, volatile-rich outer solar system objects.

So at the time of the formation of the solar system, the whole area was a big gaseous cloud of supernova debris with lots of ice. The ignition of the sun started the frost line, and pushed volatiles out of the inner solar system. However some had already been trapped in the formation of the planets, and rose to the surface as they cooled. That's where Earth's ocean came from, and we know Mars and Venus had oceans too. Presumably also Mercury, although I'm sure that was short-lived.

So yes, it's all from cometary material. But then ALL of the Earth is from cometary material, and the oceans only make up a small amount of the Earth's total mass.

Re: A newly discovered moon tunnel

#135

Post by kobeya » Mon, Oct 23, 2017, 3:18 AM UTC

njarboe wrote: post #81

pjungwir wrote: post #67

Earlier quoted context omitted.

Thank you for this answer! But then why does the water have to come from comets? Why couldn't the Earth have formed with its own water? Also, we seem to have a lot of water. It's really all from comets, a little here, a little there?

Earth likely had some water during early creation (accretion) but the best theory on how the Moon formed is that a Mars sized object hit the early Earth at the end of accretion. This blasted much of the Earth's rock part (mantle) and any water it might have had into orbit. The rock part quickly fell back to Earth and the rest condensed and collapsed to form the moon. The water and other volatilizes that were on Earth…

There's actually a lot of water in the mantle of the Earth. There's something like 3x the current ocean volume trapped in the mantle, and there are theories that pressure differentials cause this water to escape as gaseous water escapes from the atmosphere. It would explain why the ocean happens to be approximately the height of the continental shelf, and always has been. Under this theory the water simply emerged as the Earth cooled from the impact. The Moon, on the other hand, would be missing this water as the debris was mostly stripped of water content as it accreted.

Re: A newly discovered moon tunnel

#136

Post by kobeya » Mon, Oct 23, 2017, 3:23 AM UTC

cyberferret wrote: post #62

sideshowb wrote: post #57

"Let's dig a tunnel to the centre of the moon!" "You can't dig a tunnel to the centre of the moon, Blode!" "Yes I can! It will be a special tunnel, and it will go to the centre of the moon!" Anyone else remember that?

I don't recall that quip, but I do recall an episode of "Space 1999" decades ago titled "The Catacombs of the Moon" where they discover a vast underground cave system, (which turns out to be the hibernation place for a civilisation of aliens, IIRC)... The episode always had me intrigued as to whether the moon actually could have a large cave system that could be hermetically sealed and inhabited by humans to save on…

Yes, and it's one of the oldest and seriously touted plans for lunar settlement. Apollo 15 landed next to and studied a collapsed lava tube, so we even have ground truth here.

Re: A newly discovered moon tunnel

#137

Post by kobeya » Mon, Oct 23, 2017, 3:30 AM UTC

DougWebb wrote: post #78

ballenf wrote: post #27

Earlier quoted context omitted.

Are there any figures on the minimum $/gram of minerals that would justify a mining mission (presumably unmanned)? Just can't imagine that gold, platinum or any stable metal would be worth it. Maybe high grade diamonds that don't need to be extracted from other rock. The surveys would have likely identified the presence of such a high density substance and we haven't seen any mention of it. I know you probably meant…

The most common elements on the moon are quite common on the earth too; I don't think the value in mining them will ever come from bringing the mined materials back to earth. The value is going to come from having and maintaining an established base on the moon. The moon is a high point in the earth's gravity well that's full of raw materials that can be used to build things that can go further out. Mining on the moo…

The most common elements, sure. It's the rare elements that are more interesting. Many of these are rare on both Earth and the Moon because they are iron soluble and sank to the core. On Earth they get replenished from either asteroid impact or volcanism, then plate tectonics and hydration cycles slowly move the material back into the mantle or away from the site of deposit. Those processes don't exist on the Moon, so there's been ~3.5bn years of bombardment leaving precious-metal rich deposits on the surface of the Moon, where they remain until someone comes by to pick them up. You'll find that most of the Moon is boring rocks only a geologist could love, and then a bunch of super highly concentrated ores at deposit sites. And these deposit sites are not hard to find either. Just look for craters...

Re: A newly discovered moon tunnel

#138

Post by kobeya » Mon, Oct 23, 2017, 3:33 AM UTC

r00fus wrote: post #11

jccooper wrote: post #4

Earlier quoted context omitted.

Whomever can occupy it. Outer Space Treaty prohibits national claims but not use for peaceful purposes. So if you sit on it, you own it.

According to link above the treaty prohibits all sovereign claims. However, getting there can be made into a reasonable barrier to competition. Sure you can also exploit the moon, but how are you going to get there?

If you think getting to the Moon is hard, where many resources are surface extractable, look into what it takes to mine certain ores on Earth kilometers below ground in remote regions.

Re: A newly discovered moon tunnel

#139

Post by larkeith » Mon, Oct 23, 2017, 3:52 AM UTC

waegawegawe wrote: post #115

larkeith wrote: post #86

Earlier quoted context omitted.

Depending on the volume of surface ice (especially at the poles), might it be possible to produce atmosphere on a massive scale via orbital lenses or mirrors? With recent advances in solar sail technology, I can't imagine the implementation would be too far removed from current capabilities.

Think about how large of a lens you're talking about. Even if it were one hundred meters across and was able to collect 100% of the sun's energy passing through it, the amount of energy produced would be utterly insignificant compared to the problem we're discussing. And how would you get a one hundred meter lens to mars orbit? Even after that, you have to consider that we want an oxygen atmosphere, not one made of w…

The IKAROS sail (launched 2010) is 196 m^2, using aluminum as a reflector (about 90% efficiency). With regards to transferring a lens to orbit, that is a self-solving problem - a large lens or mirror can both be used as a solar sail, potentially even hauling additional mass to Mars orbit.

Mars receives 593 W/m^2 flux, so each IKAROS-sized reflector could produce about 100 KW of energy. Given the expected difficulty of large scale terraforming and colonization efforts, it seems the cost of, say, the equivalent of 10,000 IKAROS-sized mirrors (~1 GW, comparable to a large nuclear plant) would be relatively minor.

Whether that would be more cost effective than shipping an equivalently powerful reactor or other generator is questionable - it will presumably depend on our lifting capacities.

Re: A newly discovered moon tunnel

#140

Post by larkeith » Mon, Oct 23, 2017, 3:59 AM UTC

hutzlibu wrote: post #116

larkeith wrote: post #86

Earlier quoted context omitted.

Depending on the volume of surface ice (especially at the poles), might it be possible to produce atmosphere on a massive scale via orbital lenses or mirrors? With recent advances in solar sail technology, I can't imagine the implementation would be too far removed from current capabilities.

With lenses you could also burn the soil to produce gases that add up to he atmosphere ... but we want breathable atmosphere. With lot's of oxygen and very little co2. And that is a bit harder ... So you also couldn't just vaporize the ice, you need to split it up. Solar heat could be sufficient, but the water will then be missed everywhere else on mars where life wants to grow. And Mars is dry. So I would first use…

I wonder if it would be a reasonable colonization process to establish a non-breathable atmosphere, allowing postprocessing facilities to later separate oxygen from airborne water vapour.

The notable benefits from such an approach would be the ability to easily deliver asteroid-based water deposits (aim it at Mars, let reentry do the rest), as well as the significant simplification of ground based colonization technology - it's far easier to build resilient habitats for a non-breathable atmosphere than it is for a vacuum, and the risk of accidents and difficulty of venturing outside is much, much lessened (a face mask or filter and oxygen tank instead of a bulky spacesuit), not to mention the radiation protection afforded by a thick atmosphere.