NASA Targets the Moon’s Underground World

0:03Speaker 1:Welcome to Bedtime Astronomy. Explore the wonders of the cosmos with our soothing Bedtime Astronomy podcast. Each episode offers a gentle journey through the stars, planets, and beyond, perfect for unwinding after a long day. Let's travel through the mysteries of the universe as you drift off into a peaceful slumber under the night sky.

0:27Speaker 2:I want you to imagine just for a second that you are actually standing on the surface of the moon. Oh, man. Right?

0:32Speaker 1:Right?

0:33Speaker 2:The view is, I mean, it's undeniably spectacular. You've got this stark gray, heavily cratered landscape just rolling out in front of you.

0:42Speaker 3:And that absolute inky blackness of space right above.

0:46Speaker 2:Exactly. And the earth is just hanging there in the sky. But the reality of that environment is, well, it's a lot less romantic than the view.

0:57Speaker 3:Yeah, it's actually incredibly hostile.

1:00Speaker 2:It is actively trying to kill you. Because there's no atmosphere, right? And no magnetic field. So you are just being constantly bombarded by unfiltered galactic cosmic rays.

1:10Speaker 3:And the solar radiation.

1:11Speaker 2:Yeah.

1:11Speaker 3:Don't forget that.

1:12Speaker 2:Yeah, the solar radiation. On top of that, you are dealing with these wild, just massive temperature swings.

1:18Speaker 3:Because there's no air to distribute the heat around.

1:21Speaker 2:Right. So you go from like 250 degrees Fahrenheit in direct sunlight to negative 200 degrees the exact moment you step into a shadow.

1:30Speaker 3:It's an instant drop.

1:32Speaker 2:It is a beautiful but highly lethal place. So if humanity is going to transition from, you know, just planting flags to actually staying there, we have a massive logistical problem. Where do we hide?

1:45Speaker 3:It really is the defining bottleneck for long-term lunar exploration. I mean, we simply can't just pitch a tent.

1:52Speaker 2:No, definitely not a tent.

1:53Speaker 3:And hauling heavy radiation-shielded habitat modules all the way out of Earth's gravity well and landing them on the moon is just astronomically expensive.

2:03Speaker 2:Which brings us to an incredibly ambitious, newly NASA-selected project. It suggests that the answer to our survival might actually already be built.

2:13Speaker 3:Just waiting for us.

2:14Speaker 2:Right under our feet. Today, we're unpacking this mission that's setting out to explore a massive potential underground cave system on the moon.

2:21Speaker 3:It's such an exciting project.

2:23Speaker 2:We are going to explore the exact location of this mysterious lunar pit, the cutting-edge technology being sent to investigate it, and Well, what it really means for the future of human space exploration.

2:34Speaker 3:The dual nature of this mission is really what makes it so critical. It operates on two completely different timelines of lunar history.

2:42Speaker 2:Okay, how so?

2:43Speaker 3:Well, looking backward, it's a key to unlocking the moon's ancient, really violent volcanic past. But looking forward, it's a highly practical scouting mission.

2:53Speaker 2:Looking for a habitat. Right.

2:55Speaker 3:Looking for a natural, pre-built sanctuary for future astronauts. The structural geology here literally has life or death implications.

3:03Speaker 2:So to really understand this mission, we have to start with a target. We are heading to a highly specific location called the Marius Hills Pit, or MHP.

3:11Speaker 3:Right, in the Oceanus Procellarum.

3:13Speaker 2:Yeah, which is one of the moon's most volcanically diverse regions. And just to be clear, this isn't, you know, a standard impact crater.

3:21Speaker 3:No, not at all.

3:22Speaker 2:Observations from orbit show this massive, sheer vertical drop. It's a hole in the ground. that orbital imaging suggests might be a doorway into a vast underground space.

3:33Speaker 3:Formed by ancient volcanic activity, yeah. The orbital data from the Lunar Reconnaissance Orbiter is really what started this whole thing.

3:41Speaker 2:The LRO?

3:42Speaker 3:Exactly. When sunlight hits this particular pit at a specific angle, the shadows don't behave like they do in a normal bowl-shaped crater.

3:50Speaker 2:They show an overhang, right?

3:51Speaker 3:Yes. There's a distinct void stretching out beneath the surface crust.

3:56Speaker 2:See, I look at those orbital photos and Honestly, to me, a shadow is just a shadow.

4:00Speaker 3:Sure, it can be hard to interpret.

4:02Speaker 2:I mean, Earth is full of sinkholes and limestone or collapsed caverns that drop down 20 feet, hit a dirt floor, and just stop entirely.

4:10Speaker 3:Right, a dead end.

4:11Speaker 2:How do we know it's not just a shallow sinkhole? How do we know it actually goes anywhere, like a sprawling underground subway system?

4:18Speaker 3:What's fascinating here is that you have to look at the surrounding geology. The Marius Hills region is defined by ancient basaltic volcanism.

4:26Speaker 2:Okay.

4:27Speaker 3:So when we see a hole like this in a volcanic plain, the mechanics of lava tubes become the primary suspect.

4:34Speaker 2:Lava tubes. Yeah.

4:35Speaker 3:When a massive river of lava flows across the surface, it's suddenly exposed to the extreme cold of the lunar vacuum.

4:42Speaker 2:Right, that negative 200 degree shadow.

4:44Speaker 3:Exactly. So that outer layer of the lava river rapidly cools and solidifies, forming this hard, insulating crust on top.

4:52Speaker 2:Like ice freezing over a river in winter.

4:54Speaker 3:That's a great analogy. But the core of that lava river is still insulated by that crust. So it stays molten and just keeps flowing beneath that new roof.

5:02Speaker 2:So the lava is flowing through its own pipe.

5:05Speaker 3:That's the mechanism, yeah. The superheated lava continues to flow. And once the eruption ceases at the source, the remaining lava just drains out the downhill end.

5:15Speaker 2:Leaving it completely hollow.

5:16Speaker 3:What you are left with is a massive, hollow, rocky tube. But here's where the moon-specific physics completely change the scale of things.

5:25Speaker 2:Because of the gravity. Right.

5:27Speaker 3:On Earth, lava tubes might be, I don't know, a few dozen feet across before the ceiling collapses under its own weight.

5:33Speaker 2:Because Earth's gravity just pulls that heavy rock roof down.

5:37Speaker 3:Exactly. But the moon has one-sixth of our gravity.

5:41Speaker 2:One-sixth? That's a huge difference for structural integrity. It is.

5:45Speaker 3:Combined with the fact that the moon doesn't have water or wind erosion to weaken the rock over time.

5:50Speaker 2:It's perfectly preserved.

5:52Speaker 3:Because of that low gravity and stable environment. Structural modeling indicates lunar lava tubes can be hundreds of meters wide.

5:58Speaker 1:Wow.

6:00Speaker 2:Hundreds of meters.

6:01Speaker 3:You could theoretically fit entire skyscrapers inside them.

6:04Speaker 2:That is wild.

6:06Speaker 3:And the ceiling of that tube, that really thick layer of dense basaltic rock, is what makes it the ultimate sanctuary.

6:12Speaker 2:Because it blocks the radiation.

6:14Speaker 3:Yes. Basalt is incredibly dense. A ceiling just a few meters thick provides a natural, impenetrable shield against cosmic radiation.

6:23Speaker 2:Capturing all those high-energy particles before they ever reach the inside. Right.

6:28Speaker 3:It's essentially a natural bunker.

6:30Speaker 2:A pre-built bunker. And it solves the temperature problem too, doesn't it?

6:34Speaker 3:It absolutely solves the thermal problem. Because you are shielded from the direct sun in the vacuum of space, the temperature down inside a lunar lava tube is modeled to be really stable.

6:44Speaker 2:What kind of temperature are we talking about?

6:46Speaker 3:It hovers right around a comfortable negative four degrees Fahrenheit.

6:49Speaker 2:Okay, negative four still sounds pretty cold.

6:52Speaker 3:It is cold. But engineering a habitat for a constant negative 4 is infinitely easier than engineering for wild swings of 400 degrees every two weeks.

7:00Speaker 2:Right, because materials expand and contract with the heat. A constant temp is a dream for engineers.

7:07Speaker 3:Exactly.

7:07Speaker 2:Okay, so from orbit, we see the skylight. We see the shadow hinting at an overhang. But orbital cameras, you know, they can't bend light around corners.

7:16Speaker 3:No, they can't.

7:17Speaker 2:We have reached the limit of what staring from space can tell us. To know if that tunnel actually continues, we have to physically send a team down to the surface to look.

7:27Speaker 3:We have to get on the ground.

7:29Speaker 2:And that is the objective of the mission known as GIMLI.

7:33Speaker 3:Which stands for Geophysical Instruments for Marius Lunar Pit Investigation. GIMLI.

7:38Speaker 2:It's a great acronym.

7:39Speaker 3:NASA loves their acronyms. The project is spearheaded by Than Putzig, who's a senior scientist at the Planetary Science Institute, or PSI.

7:47Speaker 2:Right.

7:48Speaker 3:But what really stands out about GIMLI is the Architecture of the team he has assembled. It is a highly specialized modular collaboration.

7:56Speaker 2:It's a really fascinating roster. You have PSI driving the core science. But then you have Honeybee Robotics, which is actually a Blue Origin company, stepping in to build the instruments.

8:07Speaker 3:Managing the hardware side of things, yeah.

8:08Speaker 2:Exactly. And then you have the Norwegian Space Agency providing the ground penetrating radar.

8:13Speaker 3:Which is a very specific skill set.

8:15Speaker 2:Right. And all of this hardware is hitching a ride on a lander and rover provided through NASA's Commercial Lunar Payload Services Initiative, or CLPS.

8:24Speaker 3:Plus you have researchers from Boise State, Johns Hopkins, the Lunar and Planetary Institute, and the University of Oslo all running the data analysis.

8:32Speaker 2:It's a massive team.

8:33Speaker 3:If we connect this to the bigger picture, the days of a single space agency designing, building, and launching every single component in-house are largely over.

8:42Speaker 2:It's too slow and too expensive.

8:44Speaker 3:Exactly. Gimli perfectly illustrates this new era. It's a flawless integration of commercial entities, international agencies, and academia.

8:52Speaker 2:You lean on commercial companies like Honeybee Robotics because they just specialize in rapid development.

8:57Speaker 3:Right, building robotic actuators efficiently.

9:00Speaker 2:And the inclusion of the Norwegian Space Agency is what really caught my eye. They aren't just, you know, a random partner they pulled out of a hat.

9:06Speaker 3:No, they have highly specific expertise in deep ground radar.

9:10Speaker 2:Because of their terrestrial work mapping deep Arctic ice and glaciers in Norway, right?

9:14Speaker 3:Yes. They are taking technology optimized for penetrating miles of solid frozen material on Earth and adapting it to penetrate solid lunar basalt.

9:23Speaker 2:Without the signal just scattering everywhere.

9:25Speaker 3:It is a brilliant application of terrestrial tech to a planetary science problem.

9:29Speaker 2:I saw a quote from Amanda Hendricks, the director at PSI, and she noted how thrilling this transition is.

9:35Speaker 3:Taking a question studied from afar and finally investigating it on the ground. Right.

9:39Speaker 2:Moving from passive observation to active physical investigation. But that physical investigation faces a pretty severe hurdle when you consider the lunar surface.

9:49Speaker 3:The logistics of actually mapping this void are incredibly complex. Exactly.

9:53Speaker 2:Gimli touches down. The rover drives up to the edge of the Marius Hills pit. How do they actually... you know, see underground without digging?

10:03Speaker 3:Because they can't go inside.

10:04Speaker 2:And they can't just deploy a massive drilling rig. Bringing a heavy drill to the moon requires way too much mass.

10:10Speaker 3:And lunar regolith is awful for moving parts.

10:13Speaker 2:It's essentially microscopic, razor-sharp glass shards.

10:16Speaker 3:It destroys everything through friction.

10:17Speaker 2:So drilling is out. How do you map the unknown void below you?

10:22Speaker 3:You have to rely on a whole suite of interconnected remote sensing tools.

10:26Speaker 2:You can't just trust one sensor.

10:28Speaker 3:No, relying on a single sensor is a massive risk. So the mission uses a three-tiered approach. Ground-penetrating radar, gravimeters to measure density, and crucially, active-source seismic methods.

10:40Speaker 2:Okay, let's break those down, starting with the seismic methods, because this is the piece that Thayne Putsick's team seems most excited about bringing back.

10:46Speaker 3:It really is the core of their strategy.

10:48Speaker 2:And this essentially hasn't been done since the Apollo astronauts were up there. Active source seismology is, if I'm understanding the physics correctly, basically like echolocation or sonar.

10:59Speaker 3:But for solid rock instead of water or air.

11:02Speaker 2:Right.

11:03Speaker 3:That is a highly accurate way to visualize it. You create a control vibration, basically a thump on the surface.

11:09Speaker 2:A physical impact. Yes.

11:11Speaker 3:That impact sends acoustic waves deep into the lunar crust. And as those waves travel down, They move through solid rock at a very specific speed.

11:19Speaker 2:Okay.

11:20Speaker 3:But when they hit a boundary, like the transition from dense basalt to the absolute vacuum of an empty lava tube, the wave reflects back up to the surface.

11:29Speaker 2:It bounces back.

11:30Speaker 3:Exactly. By timing exactly how long it takes for that echo to return to a network of sensors on the surface, you can map the precise depth of the cave.

11:39Speaker 2:Wait, if it's such an effective way to map the underground, why the massive pause? We haven't given the moon an ultrasound like this since Apollo?

11:46Speaker 3:Since Apollo 14, yeah.

11:48Speaker 2:Why the long pause, and why is now the perfect time to bring it back?

11:52Speaker 3:Because doing it robotically is an absolute engineering nightmare, primarily due to Newton's third law.

11:58Speaker 2:Every action has an equal and opposite reaction?

12:01Speaker 3:Exactly. During Apollo, astronauts physically deployed explosive squibs, Or they used a handheld thumper device to generate that seismic energy.

12:10Speaker 2:They had the physical mass of a human in a spacesuit holding it down.

12:13Speaker 3:Right. They had mass and the adaptability of a human operator. If you try to automate a thumper on a lightweight rover in one-sixth gravity, you run into a severe mechanical issue.

12:25Speaker 2:If a robotic arm fires a heavy piston down into the rock to create a massive wave, the recoil is just going to launch the rover up off the ground.

12:33Speaker 3:You've identified the exact bottleneck. To generate enough kinetic energy to penetrate hundreds of meters of rock, the recoil is immense.

12:41Speaker 2:So it would just break the rover.

12:43Speaker 3:Yes. Perfecting a system that can reliably strike the ground with sufficient force, decouple that shock from the delicate chassis, and do it repeatedly.

12:52Speaker 2:That's a tough engineering problem.

12:54Speaker 3:It's taken decades of iterative engineering. Gimli is finally bringing this capability back.

13:00Speaker 2:Okay, so they used the seismic thumpers to find the floor and ceiling of the cave? How do the radar and the gravimeter fit into the toolkit?

13:09Speaker 3:Well, the ground-penetrating radar from Norway operates on a different physical principle. Instead of sound waves, it sends pulses of electromagnetic energy into the ground.

13:18Speaker 2:Okay.

13:19Speaker 3:It is highly sensitive to changes in the material properties of the rock layers. So while the seismic data gives you the gross structural boundaries of the void.

13:26Speaker 2:The radar gives you the details. Yes.

13:28Speaker 3:The radar maps the intricate layering, fractures, and the structural integrity of the basalt roof above the cave.

13:34Speaker 2:So it tells you if the roof is a solid, safe slab of rock or if it's heavily fractured and in danger of collapsing on your future habitat.

13:43Speaker 3:Exactly. You really need to know if the ceiling is going to cave in. And then you have the gravimeter, which measures minute local variations in gravitational pull.

13:52Speaker 2:Because gravity is entirely dependent on mass.

13:55Speaker 1:Right.

13:56Speaker 3:If a rover is driving over a solid block of basalt, the gravimeter registers a specific baseline reading.

14:02Speaker 2:But if the rover drives over a massive, hollow lava tube.

14:06Speaker 3:There is significantly less mass beneath it. So the gravimeter will detect a microscopic drop, a negative gravity anomaly.

14:14Speaker 2:So by layering these three datasets, the acoustic echoes from the seismology, the electromagnetic reflection from the radar, and the mass deficit from the gravimeter, Gimli gets a highly detailed map.

14:25Speaker 3:A high-resolution, three-dimensional model of subsurface properties.

14:30Speaker 2:They can calculate its exact dimensions, its volume, and its structural stability, all while safely parked on the surface.

14:36Speaker 3:It removes the ambiguity completely. This multi-tool approach is necessary to definitively confirm the presence, and the exact size, of an underground void.

14:46Speaker 2:But this forces us to play devil's advocate for a minute. We have to confront the inherent risk of planetary exploration.

14:52Speaker 3:There's always a risk.

14:53Speaker 2:What is the plan B? What happens if Gimli lands, the rover deploys... The radar powers up, the robotic thumpers strike the ground, and they find absolutely nothing.

15:04Speaker 3:Just solid rock.

15:05Speaker 2:Right. What if the overhang we see from orbit is just a trick of the light and there is no massive cavern? Is this whole mission considered a failure?

15:13Speaker 3:Absolutely not. And this is a true testament to how the team engineered the science objectives. How so? They designed a mission so that even if there is no cave, the data is invaluable. The walls of the Marius Hills pit expose layers of rock that are usually hidden.

15:28Speaker 2:This raises an interesting point that Gareth Morgan, the PSI senior scientist, brought up. Yes.

15:33Speaker 3:This raises an important question about how volcanism operated on the moon.

15:37Speaker 2:Because lava tubes are common in basaltic volcanism on Earth.

15:41Speaker 3:Right. By studying these exposed layers in the pit walls and comparing them to terrestrial caves, scientists can map how lava actually traveled on the moon.

15:51Speaker 2:The pit walls give you a cross-section.

15:53Speaker 3:Exactly. The uppermost layer of the moon is the regolith. Which has been churned up and pulverized by billions of years of micrometeorite impacts.

16:02Speaker 2:Right. It's just pulverized dust on top.

16:04Speaker 3:But beneath that is the intact bedrock. The sheer walls of the Marius Hills pit expose those original stacked layers of ancient lava flows.

16:13Speaker 2:So what does this all mean? It's basically like comparing the exposed pit walls to tree rings, right? Or the layers of the Grand Canyon.

16:21Speaker 3:That's a perfect way to look at it.

16:23Speaker 2:It's a frozen rock. physical record of the moon's violent history just waiting to be read.

16:28Speaker 3:A vertical timeline of planetary cooling. By analyzing the thickness of those exposed layers, geologists can determine the time span separating ancient eruptions.

16:38Speaker 2:Was it constant oozing or massive catastrophic eruptions millions of years apart?

16:43Speaker 3:Exactly. The pit walls hold the cadence of the moon's history.

16:47Speaker 2:But if they do find an intact lava tube, the scientific value multiplies, right?

16:51Speaker 3:Exponentially. The interior of that cave would be one of the most pristine environments in the solar system.

16:57Speaker 2:Because it's been sealed off.

16:59Speaker 3:Sealed off from the constant radiation and impact weathering on the surface. Inside a sealed tube, the original volcanic textures, maybe even trapped volatile gases, would be perfectly preserved.

17:10Speaker 2:A literal four billion year old time capsule.

17:14Speaker 3:Just waiting in the dark.

17:15Speaker 2:When you lay out the mechanics of what the Gimli mission is actually attempting, it really forces a shift in how you view the moon. For anyone listening, you aren't just tracking a science experiment with a rover taking pictures of rocks.

17:28Speaker 3:No, it's much bigger than that.

17:29Speaker 2:You are actively witnessing the groundwork for humanity's future. We are watching the era where we stop merely visiting the lunar surface and begin spelunking its depths.

17:40Speaker 3:And it leaves us with a really profound thought to mull over.

17:43Speaker 2:What's that?

17:45Speaker 3:The whole mission seeks to find a safe haven from the deadly lunar surface. If it succeeds... the very first permanent human settlements on another celestial body might be entirely underground.

17:57Speaker 2:Which completely flips the script on how we imagine space travel.

18:01Speaker 3:How will living as a subterranean species change our astronauts' relationship with space?

18:06Speaker 2:Right, you're not looking out a window at the stars.

18:09Speaker 3:Exactly. Will that classic image of staring up at the cosmos be replaced by the quiet, protective embrace of ancient basaltic rock?

18:17Speaker 2:That is a staggering thought. Engineering a life down in the absolute dark to survive the stars above. Well, thank you so much for joining us on this exploration today. It is going to be absolutely fascinating to watch the Gimli rover strike the lunar surface and see what echoes back from the deep. Until next time, keep your curiosity alive.