There Could Be Lava Tubes on the Moon, Large Enough for Whole Cities

Every year since 1970, astronomers, geologists, geophysicists, and a host of other specialists have come together to participate in the Lunar and Planetary Science Conference (LPCS). Jointly sponsored by the Lunar and Planetary Institute (LPI) and NASA’s Johnson Space Center (JSC), this annual event is a chance for scientists from all around the world to share and present the latest planetary research concerning Earth’s only moon.

This year, one of the biggest attention-grabbers was the findings presented on Tuesday, March 17th by a team of students from Purdue University. Led by a graduate student from the university’s Department of Earth, Atmospheric and Planetary Sciences, the study they shared indicates that there may be stable lava tubes on the moon, ones large enough to house entire cities.

In addition to being a target for future geological and geophysical studies, the existence of these tubes could also be a boon for future human space exploration. Basically, they argued, such large, stable underground tunnels could provide a home for human settlements, shielding them from harmful cosmic radiation and extremes in temperature.

The Hadley Rille, at the foot of the Apennine Mountains encircling the Mare Imbrium where Apollo 15 landed (NASA/JAXA)
The Hadley Rille, at the foot of the Apennine Mountains encircling the Mare Imbrium where Apollo 15 landed. Credit: NASA/JAXA

Lava tubes are natural conduits formed by flowing lava that is moving beneath the surface as a result of a volcanic eruption. As the lava moves, the outer edges of it cools, forming a hardened, channel-like crust which is left behind once the lava flow stops. For some time, Lunar scientists have been speculating as to whether or not lava flows happen on the Moon, as evidenced by the presence of sinuous rilles on the surface.

Sinuous rilles are narrow depressions in the lunar surface that resemble channels, and have a curved paths that meanders across the landscape like a river valley. It is currently believed that these rilles are the remains of collapsed lava tubes or extinct lava flows, which is backed up by the fact they usually begin at the site of an extinct volcano.

Those that have been observed on the Moon in the past range in size of up to 10 kilometers in width and hundreds of kilometers in length. At that size, the existence of a stable tube – i.e. one which had not collapsed to form a sinuous rille – would be large enough to accommodate a major city.

For the sake of their study, the Purdue team explored whether lava tubes of the same scale could exist underground. What they found was that the stability of a lava tube depended on a number of variables- including width, roof thickness and the stress state of the cooled lava. he researchers also modeled lava tubes with walls created by lava placed in one thick layer and with lava placed in many thin layers.

The city of Philadelphia is shown inside a theoretical lunar lava tube. A Purdue University team of researchers explored whether lava tubes more than 1 kilometer wide could remain structurally stable on the moon. (Purdue University/courtesy of David Blair)
The inside of a theoretical lunar lava tube, with the city of Philadelphia shown for scale. Credit: Purdue University/David Blair

David Blair, a graduate student in Purdue’s Department of Earth, Atmospheric and Planetary Sciences, led the study that examined whether empty lava tubes more than 1 kilometer wide could remain structurally stable on the moon.

Our work is somewhat unique in that we’ve combined the talents of people from various Departments at Purdue,” Blair told Universe Today via email. “With guidance from Prof. Bobet (a civil engineering professor) we’ve been able to incorporate a modern understanding of rock mechanics into our computer models of lava tubes to see how they might actually fail and break under lunar gravity.”

For the sake of their research, the team constructed a number of models of lava tubes of different sizes and with different roof thicknesses to test for stability. This consisted of them checking each model to see if it predicted failure anywhere in the lava tube’s roof.

“What we found was surprising,” Blair continued, “in that much larger lava tubes are theoretically possible than what was previously thought. Even with a roof only a few meters thick, lava tubes a kilometer wide may be able to stay standing. The reason why, though, is a little less surprising. The last work we could find on the subject is from the Apollo era, and used a much simpler approximation of lava tube shape – a flat beam for a roof.

 Mons Rümker rise on the Oceanus Procellarum was taken from the Apollo 15 while in lunar orbit.
Mons Rümker, an extinct volcanic formation on the Moon’s surface, as imaged by the Apollo 15 spacecraft while in orbit. Credit: NASA

The study he refers to, “On the origin of lunar sinuous rilles“, was published in 1969 in the journal Modern Geology. In it, professors Greeley, Oberbeck and Quaide advanced the argument that sinuous rilles formation was tied to the collapse of lava flow tubes, and that stable ones might still exist. Calculating for a flat-beam roof, their work found a maximum lava tube size of just under 400 m.

“Our models use a geometry more similar to what’s seen in lava tubes on Earth,” Blair said, “a sort of half-elliptical shape with an arched roof. The fact that an arched roof lets a larger lava tube stay standing makes sense: humans have known since antiquity that arched roofs allow tunnels or bridges to stay standing with wider spans.”

The Purdue study also builds on previous studies conducted by JAXA and NASA where images of “skylights” on the Moon – i.e. holes in the lunar surface – confirmed the presence of caverns at least a few tens of meters across. The data from NASA’s lunar Gravity Recovery And Interior Laboratory (GRAIL) – which showed big variations in the thickness of the Moon’s crust  is still being interpreted, but could also be an indication of large subsurface recesses.

As a result, Blair is confident that their work opens up new and feasible explanations for many different types of observations that have been made before. Previously, it was unfathomable that large, stable caverns could exist on the Moon. But thanks to his team’s theoretical study, it is now known that under the proper conditions, it is least possible.

The thickness of the moon's crust as calculated by NASA's GRAIL mission. The near side is on the left-hand side of the picture, and the far side on the right. Credit: NASA/JPL-Caltech/S. Miljkovic
NASA’s lunar Gravity Recovery And Interior Laboratory (GRAIL) mission calculated the thickness of the moon’s crust. Credit: NASA/JPL-Caltech/S. Miljkovic

Another exciting aspect that this work is the implications it offers for future exploration and even colonization on the Moon. Already, the issue of protection against radiation is a big one. Given that the Moon has no atmosphere, colonists and agricultural operations will have no natural shielding from cosmic rays.

“Geologically stable lava tubes would absolutely be a boon to human space exploration,” Blair commented. “A cavern like that could be a really ideal place for building a lunar base, and generally for supporting a sustained human presence on the Moon. By going below the surface even a few meters, you suddenly mitigate a lot of the problems with trying to inhabit the lunar surface.”

Basically, in addition to protecting against radiation, a subsurface base would sidestep the problems of micrometeorites and the extreme changes in temperature that are common on the lunar surface. What’s more, stable, subsurface lava tubes could also make the task of pressurizing a base for human habitation easier.

“People have studied and talked about all of these things before,” Blair added, “but our work shows that those kinds of opportunities could potentially exist – now we just have to find them. Humans have been living in caves since the beginning, and it might make sense on the Moon, too!”

In addition to Melosh, Blair and Bobet, team members include Loic Chappaz and Rohan Sood, graduate students in the School of Aeronautics and Astronautics; Kathleen Howell, Purdue’s Hsu Lo Professor of Aeronautical and Astronautical Engineering; Andy M. Freed, an associate professor of earth, atmospheric and planetary sciences; and Colleen Milbury, a postdoctoral research associate in the Department of Earth, Atmospheric and Planetary Sciences.

Further Reading: Purdue News

Can NASA’s Planetary Science Budget Be Saved?

[/caption]

“Flat is the new up,” said NASA’s new Associate Administrator for the Science Mission Directorate, John Grunsfeld, attempting to bring a bit of levity to the outlook for NASA’s proposed 2013 budget. Grunsfeld was speaking to a shellshocked community that will be taking the biggest hit in the NASA budget decrease: planetary scientists attending the Lunar and Planetary Science Conference this week in The Woodlands, Texas. There weren’t many jokes or laughs during Grunsfeld’s talk; nor from Jim Green, NASA’s Planetary Science Division Director. Both gave short remarks and then answered questions from the audience at “NASA Night,” the annual NASA Headquarters briefing event at LPSC.

“I wish I had a good succinct answer that this was punitive for overruns on the Mars Science Lab or JWST (James Webb Space Telescope), but this is not a Pavlovian system,” said Grunsfeld. “It comes down to tough trades: do we cut across the board, or do we pick some area? Sadly, it was decided that planetary science was the area.”

President Obama’s proposed FY 2013 budget would eliminate $300 million from the agency’s Planetary Sciences Division, a 21% cut from the $1.5 billion it received for 2012.

“We essentially lost the ability to create new missions,” Grunsfeld said.

Sitting among the people who, because of this proposed budget “whacking” (as Grunsfeld called it), will likely lose jobs or see their life’s work delayed or canceled, it was hard not to believe that this particular budgetary decision is wrong in every way possible. NASA would be slashing what many believe is the space agency’s most successful program.

“A 20% budget cut will likely equal 20% loss of jobs,” one commenter from the audience said. “People who land missions on Mars will lose their jobs, and when we get to the stage of landing humans on Mars, those with the know-how won’t be there.”

President Obama has stated he will see astronauts on Mars in his lifetime, so the plan to put the Mars program essentially on hold is extremely short-sighted, if not ironic.

“What a lot of people don’t realize is these cuts will most deeply impact the youth in our field,” wrote Dr. Pamela Gay in her StarStryder blog. “Many senior people who normally can find funding for themselves and a small fleet of postdocs and students will now just be funding themselves. It’s hard. It’s ugly. Especially when we work so hard to get people to get educations in this field.”

Planetary scientist Jim Bell, who is also President of The Planetary Society, along with Bill Nye, TPS’s Executive Director, both gave impassioned pleas for everyone – and especially for Grunsfeld and Green – to “fight back” against the cuts and request a review of “the largest crisis facing Planetary Science.”

Grunsfeld said he and Green are there to fight for the scientists and the missions. “Jim (Green) could have thrown his badge on the table (in response to the budget proposal), but he decided to stay and fight,” Grunsfeld said. He offered hope by reminding everyone how in 2004 when he was NASA’s chief scientist, the decision was made to not do the final repair mission to Hubble. That decision was eventually reversed. “History tends to repeat itself,” he said.

Jim Green, NASA’s Planetary Science Division Director speaking at the Lunar and Planetary Science Conference on March 19, 2012. Credit: John Blackwell/USRA.

Grunsfeld and Green both stressed how the scientists — and anyone in attendance or watching the webcast of the event — should spread the word to the general public about the importance of planetary science and also about contacting their congress-people – the ones who make the final decision about the budget.

“Without question, we must keep our eye on the ball this year,” Green said. “Our top priority for the Planetary Science Division this year is to make the landing of the Curiosity rover a success. Tell everyone about this, relate this to your neighbor. We should not let this opportunity go by without relaying it to our stakeholders, the general public. This is such an important event, and a success will compel this nation to invest more in planetary science.”

But yet, NASA’s Education and Public Outreach budget has been cut from $136 million in FY12 to $100 million in the FY13 request.

The ExoMars program. Credit: ESA

One of the most perplexing issues about the budget cuts is how NASA’s involvement in future international Mars missions, an orbiter and lander called ExoMars — with instruments and science teams already selected for parts of the mission — would be cancelled. This leaves the international partners in the lurch, damages NASA’s reputation among the international science community and puts in doubt the possibility of any future collaboration.

Yet, Green said in his talk that NASA needs to “deliver on our international commitment,” and NASA officials often tout the incredible success of the international cooperation of the International Space Station – saying it is a model for future international missions.

NASA Administrator Charlie Bolden has asked the Science Mission Directorate and Grunsfeld to reformulate an agency-wide Mars exploration strategy, where they are now suggesting a smaller, US-only Mars mission in 2018.

But could a smaller mission be less expensive and offer anywhere near the amount of science that could have been attained with the joint ExoMars mission?

“Can we recapture the Mars program?” Grunsfeld asked. “We’re not just going to look at 2018 mission but a much larger Mars program. It will be an enormous amount of work, not new analysis, but compiling inputs you (the scientists) have made in the past, and where we are in the science to see what kind of path forward makes sense.”

Grusnfeld and Green also suggested a future melding of science and human spaceflight-related missions as a way to get more funding for Mars missions. But when asked by Universe Today for an example of a “dream” Mars science mission within a scenario of a human spaceflight precursor, neither could come up with a really enticing idea.

However, Grunsfeld said science at NASA would stand to benefit from developments in human exploration and space technology. “It might be a bit of a stretch, but imagine what kind of planetary mission you could launch with a 70 metric ton launch capability,” he said, referring to the Space Launch System’s big rocket that is in the preliminary stages of being developed for future human mission to either an asteroid, the Moon or Mars.

One piece of good news: Green announced that the GRAIL mission has already received a mission extension, as well as MESSENGER, which was announced earlier. Still hanging in the balance are extended missions such as for Kepler and MER, the decisions on which will be made by this summer, Green said.

The outlook for the start-up of production of Pu-238 is not brilliant – and for any future outer planet mission, this is crucial for power for the spacecraft, and ultimately, for science. The Department of Energy did not receive any funding for a re-start, so it looks as though NASA may have to go it alone and pay the entire costs of start-up and reproduction.

Surely, it was a tough situation for Green and Grunsfeld to be in, especially for Grunsfeld – a true scientist, astronaut and ‘Hubble Hugger’ who just started his new job at NASA HQ in January. “I’m trying to look at big picture. I come from an environment where I’ve loved the partnership between humans and science. When NASA has done well overall, science has done well. So we are in tough times, and NASA needs to have a cohesive vision.”

So, it may come down to grassroots support for NASA to possibly change the current of action. While the administration proposes a budget, but it’s Congress that actually enacts the budget and appropriates the money, so anyone who is passionate on this subject needs to contact their representatives.

Inspired by Neil de Grasse Tyson’s recent suggestion during testimony to Congress (see video below) that NASA should receive a full penny on the dollar of the national budget ($37.5 Billion) instead of less than half a cent at the $17.7 billion now proposed, a student named John Zeller has started a website, Penny4NASA., which offers templates for letters to Congress, petitions on Change.org and more.

The Planetary Society is also mounting a campaign to restore the science funding to NASA.

We’ll add more links to ways to support science and planetary missions as they come in.