Lava tubes on the moon are some of the most interesting, and difficult, places to explore in the solar system. But if humanity plans to eventually have a permanent presence on the moon, the more knowledge we have about the cave systems created by those lava tubes the better.
That’s why ESA’s current focus on lunar cave exploration is so important, and another good reason to take note when it releases more information about some of the technologies leading that push. Recently, it released an update on a project known as DAEDALUS, led by Julius-Maximilians-Universität of Würzburg (JMU), with interesting new insights into the sphere shaped autonomous robot.
Always have a back up plan. Some people take that axiom to the highest levels develop backup plans for life itself. The Svalbard Seedbank is one such backup plan. Located in an ice cave in Norway it houses hundreds of thousands of seed samples in order to preserve biodiversity that is currently arranged on Earth. Ironically, if the worst models of sea level rise from climate change are realized, the Seedbank itself will be inundated by the sea and its precious cargo lost. So now a team led by a professor at the University of Arizona (UA) have proposed a much more radical idea: have the same sort of Ark, but to it much farther away from any potential catastrophic human failure – on the moon.
Infrastructure is going to be one of the biggest components of any permanent human settlement on the moon. NASA Artemis missions are focused directly on building up the facilities and processes necessary to support a moon base. ESA is also contributing both material and knowledge. Most recently they made another step in their path to explore some lava tubes and caves in the subterranean lunar world.
The first lava tube skylight discovered on the moon. Image credit: JAXA/SELENE
Could lava tubes on the Moon and Mars play a role in establishing a human presence on those worlds? Possibly, according to a team of researchers. Their new study shows that lunar and Martian lava tubes might be enormous, and easily large enough to accommodate a base.
Spectacular high Sun view of the Mare Tranquillitatis pit crater revealing boulders on an otherwise smooth floor. The 100 meter pit may provide access to a lunar lava tube. Image Credit: By NASA/GSFC/Arizona State University - http://photojournal.jpl.nasa.gov/catalog/PIA13518, Public Domain, https://commons.wikimedia.org/w/index.php?curid=54853313
When magma comes out of the Earth onto the surface, it flows as lava. Those lava flows are fascinating to watch, and they leave behind some unique landforms and rocks. But a lot of what’s fascinating about these flows can be hidden underground, as lava tubes.
These lava tubes are turning out to be a very desirable target for exploration on other worlds, just as they are here on Earth.
Artist's impression of a lunar base created with 3-d printing techniques. Credits: ESA/Foster + Partners
Between NASA, the Chinese National Space Agency, the European Space Agency and Roscosmos, there’s no shortage of plans for returning to the Moon and creating a permanent base there. Naturally, these plans have given rise to questions of where such bases should be built. So far, the top contenders have been lava tubes that have been spotted in various locations across the surface of the Moon and in the polar regions.
Whereas the polar regions are permanently shaded and appear to have abundant ice water, stable lava tubes would offer protection against the elements and harmful radiation. However, according to a new discovery presented at NASA’s Lunar Science for Landed Missions Workshop, it appears that there is a location on the Moon that ticks off both boxes – a possible lava tube that is located in the norther polar region!
NASA Lunar Reconnaissance Orbiter image showing some of the newly discovered lava tube skylight candidates at Philolaus Crater near the North Pole of the Moon. Credit: NASA/LRO/SETI Institute/Mars Institute/Pascal Lee
These pits were identified based on an analysis of imaging data from NASA’s Lunar Reconnaissance Orbiter (LRO). These images indicated the presence of small pits in the northeastern floor of the Philolaus Crater, a 70 km (43 mi)-diameter impact crater located about 550 km (340 mi) from the Moon’s North Pole. These pits could potentially be “skylights”, holes in the surface that lead to subterranean recesses.
Each pit appears to be a rimless depression measuring roughly 15 to 30 meters (50 to 11 ft) across and have shadowed interiors. Moreover, the pits are located along winding channels known as “sinous rilles” that are present along the floor of the Philolaus Crater. On the moon, these channels are thought to be the result of subterranean lava tubes that have since collapsed, or partially collapsed.
If water ice is present in the region, then these skylights could allow future explorers access to subsurface water ice that is less tainted by regolith. This presents a number of opportunities for research, and future long-term missions to the lunar surface. As Pascal Lee explained:
“The highest resolution images available for Philolaus Crater do not allow the pits to be identified as lava tube skylights with 100 percent certainty, but we are looking at good candidates considering simultaneously their size, shape, lighting conditions and geologic setting.”
In recent years, over 200 pits have been discovered by other researchers on the Moon, many of which were identified as possible skylights leading to underground lava tubes. However, this latest discovery is the first to place a possible skylight and lava tube within the Moon’s polar regions. These regions have become the focal point of research in recent years due to the fact that water ice is known to exist in the polar regions.
Within these permanently-shadowed cratered regions – particularly the South Pole-Aitken Basin – water ice is known to exist within the regolith. As a result, multiple proposals have been made to create lunar bases in the polar regions. However, there remains the challenge of how to get to that water (which would require drilling) and the fact that a permanently-shadowed region would not allow access to solar power.
This new discovery is therefore exciting for three reasons. For one, it would allow for much easier access to lunar polar ice that would be much more pure than anything drilled from the surface. Second, solar power would be available nearby, just outside each skylight. And third, these openings could provide access to a stable lava tube that contains water ice itself, much as lava tubes on Earth do.
Philolaus Crater also offers two additional bonuses when it comes a lunar settlement. Given that the crater formed in the Copernican Era (i.e. the last 1.1 billion years) it is relatively young as lunar craters go. As such, it would offer scientists with plenty of opportunities to study the Moon’s more recent geological history. Also, since the Philolaus Crater is on the near-side on the Moon, it would allow direct communications with Earth.
And as Lee added, a base in this location would also allow for some amazing views:
“We would also have a beautiful view of Earth. The Apollo landing sites were all near the Moon’s equator, such that the Earth was almost directly overhead for the astronauts. But from the Philolaus skylights, Earth would loom just over the crater’s mountainous rim, near the horizon to the southeast.”
Looking ahead, Lee and his colleagues indicate that further exploration is needed to verify whether or not these pits are lava tube skylights and whether or not they contain ice. In the future, astronauts and robots could be sent to the polar regions of the Moon in order to seek out and explore caves that have been identified from orbit. As Lee explained, this will have benefits that go far beyond lunar exploration.
“Exploring lava tubes on the Moon will also prepare us for the exploration of lava tubes on Mars,” he said. “There, we will face the prospect of expanding our search for life into the deeper underground of Mars where we might find environments that are warmer, wetter, and more sheltered than at the surface.”
And as Bill Diamond – president and CEO of the SETI Institute – explained, this discovery highlights the true nature of exploration, which goes well beyond orbiters and robotic explorers:
“This discovery is exciting and timely as we prepare to return to the Moon with humans. It also reminds us that our exploration of planetary worlds is not limited to their surface, and must extend into their mysterious interiors”.
The Lunar Science for Landed Missions Workshop was convened by the Solar System Exploration Research Virtual Institute (SSERVI) at NASA’s Ames Research Center. The purpose of the workshop was to examine the range of scientific investigations that could be conducted on the Moon, including in-situ science, network science and sample return missions.
The Marius Hills Skylight, as observed by the Japanese SELENE/Kaguya research team.
Image by: NASA/Goddard/Arizona State University
On October 5th, 2017, Vice President Mike Pence announced the Trump administration’s plan to return astronauts to the Moon. Looking to the long-term, NASA and several other space agencies are also intent on establishing a permanent lunar base there. This base will not only provide opportunities for lunar science, but will facilitate missions to Mars and beyond.
The only question is, where should such a base be built? For many years, NASA, the ESA and other agencies have been exploring the possibility of stable lava tubes as a potential site. According to new study by a team of international scientists, the presence of such a tube has now been confirmed in the Marius Hills region. This location is likely to be the site of future lunar missions, and could even be the site of a future lunar habitat.
In 2009, data provided by the Terrain Camera aboard JAXA’s SELENE spacecraft indicated the presence of three huge pits on the Moon. These pits (aka. “skylights”) were of particular interest since they were seen as possible openings to subsurface lava channels. Since then, the Marius Hills region (where they were found) has been a focal point for astronomers and planetary scientists hoping to confirm the existence of lava tubes.
Artist’s impression of a surface exploration crew investigating a typical, small lava tunnel, to determine if it could serve as a natural shelter for the habitation modules of a Lunar Base. Credit: NASA’s Johnson Space Center
Together, they examined data from the SELENE mission’s Lunar Radar Sounder (LRS) from locations that were close to the Marius Hills Hole (MHH) to determine if the region hosted stable lava tubes. Such tubes are a remnant from the Moon’s past, when it was still volcanically active. These underground channels are believed to be an ideal location for a lunar colony, and for several reasons.
For starters, their thick roofs would provide natural shielding from solar radiation, cosmic rays, meteoric impacts, and the Moon’s extremes in temperature. These tubes, once enclosed, could also be pressurized to create a breathable environment. As such, finding an entrance to a stable lava tube would the first step towards selecting a possible site for such a colony.
As Junichi Haruyama, a senior researcher at JAXA and one of the co-authors on the study, explained in a University of Purdue press release:
“It’s important to know where and how big lunar lava tubes are if we’re ever going to construct a lunar base. But knowing these things is also important for basic science. We might get new types of rock samples, heat flow data and lunar quake observation data.”
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. Credit: Purdue University/courtesy of David Blair
Granted, the LRS was not specifically designed to detect lava tubes, but to characterize the origins of the Moon and its geologic evolution. For this reason, it did not fly close enough to the Moon to obtain extremely accurate information on the subsurface. Nevertheless, as SELENE passed near the Marius Hills Hole, the instrument picked up a distinctive echo pattern.
This pattern was characterized by a decrease in echo power followed by a large second echo peak. These two echoes correspond to radar reflections from the Moon’s surface, as well as the floor and ceiling of the open lava tube. When they analyzed this pattern, the research team interpreted it is evidence of a tube. They found similar echo patterns at several locations around the hole, which could indicate that there is more than one lava tube in the region.
To confirm their findings, the team also consulted data from NASA’s Gravity Recovery and Interior Laboratory (GRAIL) mission. Consisting of two spacecraft, this collaborative effort collected high-quality data on the Moon’s gravitational field between 2011 and 2012. By using GRAIL data that identified mass deficits under the surface, which are evidence of caverns, the team was able to narrow down their search.
Jay Melosh, a GRAIL co-investigator and Distinguished Professor of Earth, Atmospheric and Planetary Sciences at Purdue University, was also a co-author on the paper. As he explained:
“They knew about the skylight in the Marius Hills, but they didn’t have any idea how far that underground cavity might have gone. Our group at Purdue used the gravity data over that area to infer that the opening was part of a larger system. By using this complimentary technique of radar, they were able to figure out how deep and high the cavities are.”
Arched passages in the main tube show the classic lava tube shape. The floor was the crust on a former lava lake that fell inward as it drained from beneath. Credit: Dave Bunnell/Under Earth Images/Wikipedia Commons
On Earth, stable lava tubes have been found that can extend for dozens of kilometers. To date, the longest and deepest to be discovered is the Kazumura Cave in Hawaii, which is over a kilometer (3,614 feet) deep and 65.5 km (40.7 mi) long. On the Moon, however, lava tubes are much larger, due to the fact that the Moon has only a fraction of the Earth’s gravity (0.1654 g to be exact).
For a lava tube to be detecting using gravity data, it would need to be several kilometers in length and at least one kilometer in height and width. Since the tube in Marius Hills was detectable, it is likely big enough to house a major city. In fact, during a presentation at the 47th Lunar and Planetary Conference, researchers from Purdue University showed GRAIL data that indicated how the tube beneath the MHH could be large enough to house Philadelphia.
This most recent study was also the subject of a presentation at the 48th Lunar and Planetary Conference. Similar evidence of possible stable lava tubes in the Sea of Tranquility was also obtained by the Lunar Reconnaissance Orbiter (LRO) back in 2010. However, this latest combination of radar and gravity data has provided the clearest picture yet of what a stable lava tube looks like.
Similar evidence of lava tubes has also been discovered on Mars, and possible even Mercury. On Mars in particular, chains of pit craters, broad lava fans, skylights and partially collapsed lava tubes all indicate the presence of stable tubes. Based on this latest study, future mission to the Red Planet (which could include the creation of a habitat) might also entail the investigation of these features.
In fact, lava tubes could become the means through which a human presence is established throughout the Solar System someday!
Images of Mercury's northern polar region, provided by MESSENGER. Credit: NASA/JPL
Welcome back to another installment in the “Definitive Guide to Terraforming” series! We complete our tour of the Solar System with the planet Mercury. Someday, humans could make a home on this hostile planet, leading to the first Hermians!
The planet Mercury is an intensely hot place. As the nearest planet to our Sun, surface temperatures can get up to a scorching 700 K (427° C). Ah, but there’s a flip-side to that coin. Due to it having no atmosphere to speak of, Mercury only experiences intensely hot conditions on the side that is directly facing the Sun. On the nighttime side, temperatures drop to well below freezing, as low as 100 K (-173° C).
Due to its low orbital period and slow rate of rotation, the nighttime side remains in the dark for an extended period of time. What’s more, in the northern polar region, which is permanently shaded, conditions are cold enough that water is able to exist there in ice form. Because of this, and a few reasons besides, there are many who believe that humanity could colonize and even terraform parts of Mercury someday.
Map showing variations in the lunar gravity field, as measured by NASA's Gravity Recovery and Interior Laboratory (GRAIL) . Credit: NASA/JPL-Caltech/MIT/GSFC
For years, scientists have been hunting for the stable lava tubes that are believed to exist on the Moon. A remnant from the Moon’s past, when it was still volcanically active, these underground channels could very well be an ideal location for lunar colonies someday. Not only would their thick roofs provide naturally shielding from solar radiation, meteoric impacts, and extremes in temperature. They could also be pressurized to create a breathable environment.
But until now, evidence of their existence has been inferred from surface features such as sinuous rilles – channel-like depressions that run along the surface that indicate the presence of subterranean lava flows – and holes in the surface (aka. “skylights”). However, recent evidence presented at the 47th Lunar and Planetary Science Conference (LPSC) in Texas indicates that one such stable lava tube could exist in the once-active region known as Marius Hills.
Artist's concept of a terraformed moon. According to a new study, the Moon may have had periods of habitability in its past where it had an atmosphere and liquid water on its surface. Credit: Ittiz
Welcome back to our ongoing series, “The Definitive Guide To Terraforming”! We continue with a look at the Moon, discussing how it could one day be made suitable for human habitation.
Ever since the beginning of the Space Age, scientists and futurists have explored the idea of transforming other worlds to meet human needs. Known as terraforming, this process calls for the use of environmental engineering techniques to alter a planet or moon’s temperature, atmosphere, topography or ecology (or all of the above) in order to make it more “Earth-like”. As Earth’s closest celestial body, the Moon has long been considered a potential site.
All told, colonizing and/or terraforming the Moon would be comparatively easy compared to other bodies. Due to its proximity, the time it would take to transport people and equipment to and from the surface would be significantly reduced, as would the costs of doing so. In addition, it’s proximity means that extracted resources and products manufactured on the Moon could be shuttled to Earth in much less time, and a tourist industry would also be feasible.
