Explosive volcanism on the Moon: What if I told you NASA was looking to turn what’s left over into rocket fuel?
Earth isn’t the only place with explosive volcanoes like Krakatoa or Mount St. Helens; the Moon has them too, and NASA is looking at ways to turn lunar volcanic ash into rocket fuel. The Moon’s explosive volcanoes are slightly different than the ones here on Earth, so let’s take a closer look!
First, we have to understand that, unlike terrestrial volcanoes which can be very active, lunar volcanoes are all extinct. Earth’s core and mantle are still active and churning, fueling the heat, pressure, and energy necessary to keep our volcanoes active and healthy. In contrast, the Moon’s mantle and magma have cooled deep in the subsurface, so when we study the Moon’s volcanoes, we’re studying things that were typically active billions of years ago.
Visualization of the Apollo 15 landing site created from Lunar Reconnaissance Orbiter (LRO) data. Near foreground shows Hadley Rille, an ancient lava channel. Image from “Apollo 15 Stand-Up EVA” video from NASA Goddard: Apollo 15 Stand-Up EVA (youtube.com).
What are Moon volcanoes made out of?
Even though the Moon is an extraterrestrial body, it’s more similar to Earth than you might think. That’s because approximately 4.5 billion years ago, a giant impact between a Mars-sized protoplanet and a proto-Earth formed our modern Earth-Moon system. The impact between these two protoplanets melted, churned up, and redistributed the elements and minerals between the two bodies, which now share many characteristics.
Volcanoes on the Moon once erupted in similar ways to how volcanoes on Earth now do – magma at great depths have gases and liquids at high pressure, and when the pressure gets too high (which can happen for a lot of reasons) it erupts onto the surface. Some volcanoes erupt “effusively,” which create lava flows and lava channels. Other lunar volcanoes are “explosive” and make lava fountains like those in Hawai’i, or bursts of gas like those at Stromboli in Italy. Earth’s volcanoes have much more gas in the magma, and create much larger eruptions like the Mount St. Helens eruption in 1980 or the largest Yellowstone eruption from 2.1 million years ago. Lunar volcanoes are slightly calmer than this, and will have a few other differences that are important to consider.
First, we know the Moon is smaller than Earth, so there’s lower gravity. (If you haven’t seen a compilation reel of Astronauts tripping on the Moon, you’re missing out!) With lower gravity, pyroclasts (literally “fire pieces,” or the pieces of rock and glass that shoot out of an explosive volcano) can fly farther on the Moon than they would on Earth. So explosive lunar volcanoes spread out more and don’t build cone structures as easily as they would if they were on Earth. Adding to the low gravity, the Moon doesn’t have a thick atmosphere like Earth does, so there’s no air resistance to slows down the pyroclasts’ trajectory. On Earth, air resistance helps build cones and keep the rocks and particles close to the volcanic vent. On the moon, pyroclasts can fly really far, forming “lunar pyroclastic deposits” instead of volcanic cones. It’s these lunar pyroclastic deposits that may contain resources that necessary for exploration into the solar system.
Although not our Moon, this limb photo of Jupiter’s volcanic moon, Io, shows a perfect example of an explosive eruption on a body without an atmosphere, lofting pyroclasts into space from the surface. This is likely very similar to what was happening on our Moon billions of years ago. Check out his link for a video of the eruption: NASA SVS | Io Erupts. Image Public Domain: NASA's Goddard Space Flight Center; NASA/JPL/University of Arizona.
How do you make rocket fuel out of rocks?
There are many potential resources on the Moon that can help us explore the solar system without having to bring everything from Earth. Oxygen is a valuable resource because it is a component of rocket fuel, water, and can be used for, you know… breathing. It also happens to be the most common element found in most minerals on Earth and on the Moon. But separating the oxygen from the rest of the mineral structures is very difficult, and often requires a lot of energy (sometimes too much energy for the value of the oxygen you get). Lunar pyroclastic deposits, however, have minerals and elements that take less energy to pull oxygen from than other rocks found on the Moon.
Astronaut Jack Schmitt uses a rake tool to collect lunar samples during Apollo 17. Image public domain, NASA.
Pyroclastic deposits often have a lot of glass, similar to obsidian from a volcano on Earth. This glass is usually found as tiny droplets and beads, which can be easily crushed. Glass and minerals both have silica and oxygen atoms, glass lacks an ordered crystal structure. That means the bonds between atoms and molecules in glass droplets are easier to break apart than they are in a mineral, so you get more oxygen out of the glass than you do from the minerals for the same amount of energy.
Lunar pyroclastic deposits can also have ilmenite, which is a mineral made of titanium and iron bonded to oxygen. When we process the deposits to pull out the oxygen, we may be able to recover the titanium and iron metals to use as raw materials. It’s important to consider deposits like this as not just for a single resource, but for many levels of use. There are many companies testing technologies to 3D print with crushed up rock and soil, and also building habitats and structures out of lunar dust simulants. The raw material for these 3D printing technologies must be fine-grained and very homogenous (meaning you can’t have a lot of different grain sizes). Turns out one of the most fine-grained and homogenous types of deposits on the Moon are lunar pyroclastic deposits! That means that this one resource could be one of the best sources for oxygen, titanium, iron, AND construction material on the Moon.
Want to learn more about lunar pyroclastic deposits and how they relate to the “effusive” style of volcanism? Check out this paper by Astrogeology Physical Scientist Lori Pigue et al.:
Follow our journey to learn more about lunar resource assessments and the future of in situ resource utilization!
Circular 1507: Assessment of Lunar Resource Exploration in 2022 (usgs.gov)
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