Or is earth the only world in the inner solar system with caves.
I did an research and find this
Note that many caves here on Earth are the result of erosion of stone or dirt by water. These would not appear on the moon, but may be on Mars.
NASA reports caverns hundreds of feet deep.
"these caverns are skylights to lava tubes, so we know such tunnels can exist intact at least in small segments after several billion years."
In fact, lunar caverns are considered prime candidates for colonization. The advantages are pretty obvious. The temperature would be a balmy 7 degrees Fahrenheit a couple hundred feet below the lunar surface and provide protection from meteors and radiation. The moon is not tectonically active so they would be quite stable.
The possibility of lunar caves isn't a new idea. http://en.wikipedia.org/wiki/The_First_Men_in_the_Moon
This is incorrect. Lunar seismic events occur as a consequence of tidal stresses, meteoroid impact and possible tensions generated in association with ongoing mantle cooling.
Apollo seismometers recorded events with body wave magnitudes of 5.5. Given the comparatively short time these instruments functioned - less than a decade - it seems plausible that the maximum magnitude of event that might be experienced could easily be an order of magnitude higher.
Was that humour? I've never heard -14oCelsius called balmy before.
Perhaps you are thinking of the LRO data from 2012 where they identified apparent compression cracks that could be mere millions of years old - re: http://arstechnica.com/science/2012/02/recent-formations-say-the-moons-not-dead-yet/. Note as well there is a difference between tectonic and seismic activity - http://www.lpi.usra.edu/education/explore/shaping_the_planets/tectonism.shtml.
Compared to the lunar surface temperature, which ranges from -243F to +253F - re: http://www.space.com/18175-moon-temperature.html , a temperature of +7F would qualify as 'balmy', IMO.
Let's address the central point first: if there is seismic activity - and there is - you cannot conclude, without further evidence, that the lava tubes would be stable. The observed collapsed state of some tubes may have occurred a billion years ago, or a century ago. Without further study, preferably on-site, it would be precipitate to assume that they would be "quite stable".
The only LRO work relating to tectonics that I am aware of has identified potentially recent tensional cracks, not compressional as you suggest. Indeed the article you linked to confirms that tension is involved, as is clear from the fact that the evidence is based upon the presence of fresh graben.
These may be, as you note, mere millions of years old. That is, in a geological context, current.
Finally, tectonics relates to structural displacements. The 'engine' for these structural displacements is incidental. Impact or tidal stresses can both generate tectonic activity.
And, to repeat, the central point of my post is that if the moon is experiencing seismic events the stability of lava tubes can not be automatically relied upon.
Your hand waving arguments do not alter the fact the lunar crust is far more stable than earth. Of course there is always the possibility a comet could crash into the moon [or earth] tomorrow. You should consider a refresher course in tectonics - no molten core, no tectonics.
1. Please specify which part of my argument constitutes hand-waving.
2. Now, you assert that the lunar crust is more stable than the Earth. That is not in dispute. Why even mention it?
What is in dispute is your statement that "the lunar crust is not tectonically active and so they (the lava tubes) would be stable."
I have addressed this in two parts. Firstly, I have asserted that seismometers on the lunar surface have recorded significant seismic events. You have not disputed that, but if you do I shall provide appropriate citations.
Secondly, you appear hung up on a particular definition of tectonics that excludes activity related to tidal effects or impacts. To be clear, are you asserting that tectonics cannot be related to either of these effects?
3. Terrestrial tectonics is ultimately controlled by temperature contrasts within the mantle. These would exist whether or not the core was molten. Do you dispute this?
I do not dispute seismic activity on the moon, merely your unconventional view of tectonics. Quoting from http://www.lpi.usra.edu/education/ex...ectonism.shtml, "Tectonic activity is caused by heat loss; all the terrestrial planets passed through a molten (or nearly molten) stage early in their development and they have been cooling ever since. ... Earth, and Mars, are large enough to have remained hot inside and still have active tectonism. Smaller bodies, such as the Moon and Mercury, have cooled further and are not thought to be presently active ... Mercury and the Moon are no longer tectonically active". Tidal forces and impacts are generally not sufficiently energetic to cause tectonic activity. An exception can be made in certain cases involving the moons of giant planets [e.g., Jupiter], where tidal forces are sufficient to trigger volcanism.
Recent calculations appear to suggest the possibility of a soft, partially molten lunar core.
“A smaller celestial body like the Moon cools faster than a larger one like the Earth does. In fact, we had thought that volcanic activities on the Moon had already come to a halt. Therefore, the Moon had been believed to be cool and hard, even in its deeper parts. However, this research tells us that the Moon has not yet cooled and hardened, but is still warm. It even implies that we have to reconsider the question as follows: How have the Earth and the Moon influenced each other since their births? That means this research not only shows us the actual state of the deep interior of the Moon, but also gives us a clue for learning about the history of the system including both the Earth and the Moon.”
It seems to me that while you fellows argue the definition of "tectonics" we are missing the larger point. Especially since you both agree that by whatever definition or cause the Moon has substantially less activity than the Earth, yet we have people in mines many miles deep on Earth.
All that really matters here is whether or not these lava tubes would be or could be made to be viable living quarters, saving massive amounts of time, energy and money. If all they would require is some shoring up to prevent large scale collapse and some smaller prevention of falling debris, and probably some filtration systems for the abrasive moon dust, this would be an important discovery.
There even exist high density sprayable expanding foams that can do much of this work, especially if layered with light rebar and steel mesh. Working out the details after that shouldn't be that difficult given a decent payoff because the biggest obstacle is still what it costs per pound to deliver supplies.
The willingness to spend such huge sums of money and take such risks is only really a difference of scale compared to the Gold Rush. I'm not certain what presently would fill the bill... maybe a discovery of million metric tons of relatively pure titanium ore? or in a few decades, several hundred metric tons of pure, potable water?
Whatever it might be we still are faced with requiring reasonable transportation costs and present state chemical rockets will not fill the bill. We rattle off 240,000 miles like it was nothing but it is a LOT of nothing and the gravity holding us here may be the weakest force, but it is certainly sufficient to keeping us here for a very long time, absent some breakthrough in propulsion systems.... IMHO, of course.
My view is not unconventional. Your knowledge of geology appears to be limited.
Here are some examples of impact tectonics in the literature:
Lana, C. et al Impact tectonics in the core of the Vredefort dome, South Africa: Implications for central uplift formation in very large impact structures. Meteoritics & Planetary Science 38, Nr 7, 2003.
Osinski, G.R. and Spray, J.G. Tectonics of complex crater formation as revealed by the Haughton impact structure, Devon Island, Canadian High Arctic Meteoritics & Planetary Science 40, Nr 12, 2005
You, Z-d and Kiu, R Research on Impact Tectonics and Impactites: Status and Prospects Journal of Geomechanics 2008-1
Springer-Verlag have published an entire book, titled Impact Tectonics. Your belief that I am using the term unconventionally is apparently borne of using superficial sources for your information. These are excellent for neophytes, but they necessarily simplify, often by omission.
I see that you do now concede that tectonic effects can be generated through tidal stresses, a point I made in my initial post. To avoid further assertions of unconventional usage, here is a pertinent citation on that form of tectonics.
Greenberg, R. et al, Tectonic Processes on Europa: Tidal Stresses, Mechanical Response, and Visible Features Icarus 135, 1998
Ophiolite, apparently you consider yourself more an authority on tectonics than the Lunar and Planetary Institute. Your enthusiasm is laudatory, responding to posts with 'this is incorrect' could be viewed as provocative. Furthermore, asserting dissent in matters that were never disputed is disingenuous. I am, however, curious. Are you saying the moon suffers sufficient tidal and impact stresses to raise reasonable doubts over the stability of lunar lava tubes? As I recall, this was the original issue.
This is a very delayed reply. Apologies for that. I consider that I have a good understanding of how to interpret the wealth of research related to the issue, including that from the LPI. I believe I have demonstrated that with the citations I have provided.
This is a science forum. I do make the assumption that members will welcome the correction of statements that are wrong. If something is incorrect I believe the appropriate response is to point this out. The objective is not to provoke, but to inform.
I abhor that behaviour in others. If I appear guilty of it, it is due to misinterpretation on my part. Point out where I have done it and I shall correct it.
It certainly raises doubts. I think considerably more research would be required to determine if these were reasonable, or not.
Separate names with a comma.