Data from GRAIL spacecraft suggest moon may have large lava tubes

December 19, 2016 by Bob Yirka, Phys.org report
Credit: CC0 Public Domain

(Phys.org)—A team of researchers with Purdue University has found evidence from lunar-mapping spacecraft that the moon may have large lava tubes that could conceivably be used to house astronauts and supplies. In their paper published in the journal Icarus, the team describes their study of data from NASA's Gravity Recovery and Interior Laboratory (GRAIL) twin spacecraft and outline the evidence for large lava tubes.

Prior research here on Earth has shown that lava flowing across a surface can form a shell of sorts as it cools, and when the shell collapses, a hollowed-out underground space remains—geologists call them lava tubes. Examples have been found in Hawaii and Iceland. Now, the researchers at Purdue believe they have found that such structures might exist just below the surface of the moon in some places as well.

The evidence from GRAIL consists of very small variations in the moon's , suggesting differences in density below the surface. There is also some evidence of skylights in photographs taken of the moon near the areas of the gravitational variations. Skylights are areas on the surface that occur when part of a lava tube collapses creating a window of sorts into the tube below. The team built a geology-based computer model using the data they had gathered from GRAIL and the photographs, along with other known information about lava tubes here on Earth and other features unique to the moon. The model then offered predictions regarding the possible existence of lava tubes below the of the moon and how big and stable they might be—the researchers reasoned that they could be much larger than those found on Earth due to less pressure from gravity.

The model indicated that were likely present and that they could be as wide as three miles across and still remain stable. Such a wide, long tube, the researchers note, might be an ideal form of shelter for future astronauts—they could live in the tubes along with all their gear free from the fear of being struck by space debris and the constant barrage of solar radiation. It would likely be easier to manage temperature control as well, making life less dangerous for future residents.

Explore further: Theoretical study suggests huge lava tubes could exist on moon

More information: David M. Blair et al, The structural stability of lunar lava tubes, Icarus (2017). DOI: 10.1016/j.icarus.2016.10.008

Abstract

Mounting evidence from the SELENE, LRO, and GRAIL spacecraft suggests the presence of vacant lava tubes under the surface of the Moon. GRAIL evidence, in particular, suggests that some may be more than a kilometer in width. Such large sublunarean structures would be of great benefit to future human exploration of the Moon, providing shelter from the harsh environment at the surface—but could empty lava tubes of this size be stable under lunar conditions? And what is the largest size at which they could remain structurally sound? We address these questions by creating elasto-plastic finite element models of lava tubes using the Abaqus modeling software and examining where there is local material failure in the tube's roof. We assess the strength of the rock body using the Geological Strength Index method with values appropriate to the Moon, assign it a basaltic density derived from a modern re-analysis of lunar samples, and assume a 3:1 width-to-height ratio for the lava tube. Our results show that the stability of a lava tube depends on its width, its roof thickness, and whether the rock comprising the structure begins in a lithostatic or Poisson stress state. With a roof 2 m thick, lava tubes a kilometer or more in width can remain stable, supporting inferences from GRAIL observations. The theoretical maximum size of a lunar lava tube depends on a variety of factors, but given sufficient burial depth (500 m) and an initial lithostatic stress state, our results show that lava tubes up to 5 km wide may be able to remain structurally stable.

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12 comments

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barakn
5 / 5 (7) Dec 19, 2016
Prior research here on Earth has shown that lava flowing across a surface can form a shell of sorts as it cools, and when the shell collapses, a hollowed-out underground space remains—geologists call them lava tubes

Care to cite your source? I bet you can't, because this is a garbled understanding of lava tube formation. The shell that forms is the tube, so it can't collapse as stated and still be a tube. In reality, a river of lava can form a shell on its surface that prevents the interior from freezing and allows it to keep flowing. Eventually, either due to the end of the eruption or an upstream diversion of lava, all the lava in the tube drains out, leaving behind the hollow, uncollapsed shell.
gkam
1 / 5 (5) Dec 19, 2016
"may have large lava tubes that could conceivably be used to house astronauts and supplies."
-------------------------------

Or huge Tube Worms!!
Mayday
5 / 5 (1) Dec 19, 2016
I've been talking about these lava tubes for years. It astounds me how obsessed NASA, our scientists, and the media are with focusing solely on surface features across the Solar System. The big story will be found below the surface. The potential is too great to ignore. On the Moon, on Mars, Ceres, etc. Can we just get on with it now?
Rockguy
5 / 5 (1) Dec 19, 2016
@barakn
First off this is just a summary article of the paper so the sources would be in the paper. Second the summary is not the same as the abstract. I often find writers will use simpler explanations than the author(s) of the scientific paper itself. I find that your explanation is not quite correct either. My source: https://en.wikipe...ava_tube Also from Earth Portrait of a Planet by Stephen Marshak P239 C2 P2: "If lava drains out of the tunnel, an empty space known as a lava tube develops. Eventually during the final stages of cooling the interior of a thick lava flow contracts and fractures into roughly hexagonal columns , a type of fracturing called columnar jointing." So while draining is part of it so is fracturing.
Whydening Gyre
4.7 / 5 (3) Dec 19, 2016
I've been talking about these lava tubes for years. It astounds me how obsessed NASA, our scientists, and the media are with focusing solely on surface features across the Solar System. The big story will be found below the surface. The potential is too great to ignore. On the Moon, on Mars, Ceres, etc. Can we just get on with it now?

Think I read bout these in Popular Science, back in the 60's...
gkam
1 / 5 (4) Dec 19, 2016
I still like the worm idea better.
TrollBane
5 / 5 (1) Dec 20, 2016
So it's not green cheese, it's Swiss!
TheGhostofOtto1923
3.7 / 5 (3) Dec 20, 2016
Here's a nice pic of a skylight
https://nssphoeni...va-tube/

-Heinlein wrote a story about a large lunar cavity used as an air reservoir that people would fly around in by strapping on wings-
TheGhostofOtto1923
3 / 5 (2) Dec 20, 2016
Eventually, either due to the end of the eruption or an upstream diversion of lava, all the lava in the tube drains out leaving behind the hollow, uncollapsed shell
Here's an example of an undrained tube. They're common.
http://www.goodea...ube.html

-And here's a very familiar example of a collapsed tube.
http://adsabs.har....3....1H
barakn
3 / 5 (2) Dec 20, 2016
The second sentence of Marshak's quote is simply a second example of something that can happen to a lava flow, not something that is specifically involved in the creation of a lava tube. Note that columnar jointing is what happens to thick beds of slowly cooling lava, whereas the shell of a lava tube is thinner and formed rapidly due to its exposure to the atmosphere (the walls and floor of the tube will also cool more rapidly than the surrounding bulk). It's possible that a thicker lava tube might develop columnar jointing, but as noted the fact that it "contracts and fractures" means this sort of tube will be prone to collapsing and forming a non-tube.
BendBob
not rated yet Dec 26, 2016
I wish I could recall the authors' name who wrote about bubbles that formed from the lunar lava; which allowed a device to move the air in a circular way so "free-flight" could be done. Yes, there was lunar gravity in the story, but the air was moving such that the wings you fit on the upper torso/arms allowed flight. He wrote lots of short stories, I know someone will remind me shortly, hehe, oh - maybe it was Heinlein!?!
TheGhostofOtto1923
1 / 5 (1) Dec 27, 2016
I wish I could recall the authors' name who wrote about bubbles that formed from the lunar lava; which allowed a device to move the air in a circular way so "free-flight" could be done. Yes, there was lunar gravity in the story, but the air was moving such that the wings you fit on the upper torso/arms allowed flight. He wrote lots of short stories, I know someone will remind me shortly, hehe, oh - maybe it was Heinlein!?!

https://en.wikipe...om_Earth

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