A new lunar crater + Searching for signs of alien technology

[MUSIC PLAYING] FLORA LICHTMAN: Hey, it’s Flora, and you’re listening to Science Friday. Next time you look up at the Moon, take a moment to consider its craters. Because the Moon’s surface is so stable, no rain, no wind, no erupting volcanoes, the craters you see on the moon may have been there for millions, even billions of years.

But there is a new kid on the block that’s getting some attention. Sometime between April 11 and May 22, 2024, something smacked into the moon, creating a new crater about the size of two football fields across and over 140 deep. And lunar scientists are excited.

Dr. Tyler Powell is a planetary scientist at the Johns Hopkins Applied Physics Laboratory. Hey, Tyler. Welcome to Science Friday.

TYLER POWELL: Hey, Flora. Thanks for having me.

FLORA LICHTMAN: Thanks for being here. So is that true? Are you indeed excited about this?

TYLER POWELL: Yeah, yeah, it’s super exciting. It’s a really cool reminder that the Moon and planets are constantly evolving, which is just really cool.

FLORA LICHTMAN: How big a rock do you need to make a crater of this size?

TYLER POWELL: Oh, that’s a good question. We have a pretty good understanding of cratering mechanics. These impactors are coming in super, super fast.

At the Moon, they impact at usually around 20 kilometers per second. So it’s a 220-meter diameter crater, and something of this size is probably formed by an impactor that’s maybe 10 or 20 meters across, so much, much smaller in diameter and also mass than you might think.

FLORA LICHTMAN: What are you interested in learning from this?

TYLER POWELL: Yeah, so the main thing that’s interesting about this crater is its size and its rarity. So this is a 222-meter impact crater that we know formed in spring 2024. And it was discovered in these repeat images from the Lunar Reconnaissance Orbiter camera. And basically change detection between images before and after have revealed many craters like this that are much smaller, but this one is by far the largest.

The next largest that we’ve observed is less than a third the size at about 70 meters. Something of this size is expected to form once every maybe 130 years, so it’s extremely rare. It’s unlikely to be exceeded maybe in our lifetimes. And yeah, the most exciting thing is it’s a really unique opportunity to study a pristine crater that hasn’t been degraded by later impact craters or other effects at basically time equals zero.

I think one of the things that’s most interesting about one of these pristine craters is that were able to tease out these super faint changes to the surface that the crater has caused. So we’ve looked at this with the Diviner instrument. This is a thermal instrument on the Lunar Reconnaissance Orbiter, the same orbiter as the camera.

It measures the surface temperatures during the day but also at night. And basically, the surface of the Moon heats up during the day and cools off at night. And these nighttime temperatures are basically sensitive to the kind of physical properties of the surface, where things like rocks hold on to a lot of heat, so they stay warm at night, and finer grained material, like the fine-grained dust that covers most of the lunar surface, cools off quickly.

It’s kind of like if you’ve ever been to the beach at night and you step out onto the sand. The sand is usually colder than the sidewalk that retains a lot of heat. So when you look at a nighttime temperature map of the Moon, you’ll see areas that are warm because of rocks and then also these cold spots that are colder because the regolith is fluffier than other regions. And this is one example of that, where out to a pretty huge distance, a 7-kilometer-diameter region that’s been fluffed up by this comparatively small 200-meter crater.

FLORA LICHTMAN: And so that fluffy regolith loses heat more quickly than the packed-down dust.

TYLER POWELL: Yes, yes.

FLORA LICHTMAN: So you’re really learning about these sort of microclimates on the Moon. Why do you care about that?

TYLER POWELL: I think the main reason we care is that impact craters are one of, if not the most common geologic process in the solar system. So understanding how they modify their surroundings is really important for interpreting, really, everything in planetary science.

It’s also important for lunar samples, where we collect these samples of regolith that contain grains that have been mixed by craters. And now we’re coming to understand that they’ve been mixed by these distant impact crater processes as well. These physical properties of the surface are potentially relevant for future landed admissions for rovers, astronauts or potentially construction on the Moon because they represent a physical change to the surface.

The Apollo 16 mission, actually, happened to land in an old and faded cold spot, though they didn’t it at the time. And the astronaut footprints were actually slightly deeper there than at other locations. So this physical change to the surface that we’re inferring from orbital observations is actually something measurable at the human and rover scale. So understanding how these affect the regolith and its properties could be relevant for exploration.

FLORA LICHTMAN: That’s really cool. Doctor Tyler Powell is a planetary scientist at the Johns Hopkins Applied Physics Laboratory. Thanks for being here today.

TYLER POWELL: Thanks so much. Happy to be here.

FLORA LICHTMAN: After the break, looking at lunar dust, not for an impact crater but for traces of alien technology. Stay with us.

[MUSIC PLAYING]

While we’re digging on the Moon, a recent proposal suggested moon dust might be a good place to hunt for traces of an alien civilization. It’s called a technosignature. Instead of looking for biology, you’re looking for some sign of technology that could only be produced by intelligent life.

Dr. Sofia Sheikh is a technosignature research scientist at the SETI Institute. Welcome.

SOFIA SHEIKH: Thank you for having me.

FLORA LICHTMAN: Thanks for being here. In this hypothetical, what would you be looking for in lunar regolith?

SOFIA SHEIKH: Yeah, so I know it kind of sounds like a bit of a wacky proposal off the bat. But in reality, we know that, on Earth, humans create technology. And then even when humans are long gone from an area, the technology that we create can persist. Things like ruins or arrowheads or shards of pottery often indicate human presence in an area even long after the people who built that technology have moved on or passed away.

And so this idea of looking for technosignatures in lunar regolith is kind of an extension of that same logic. And what we would be looking for is in some ways very similar to what archaeologists look for on the Earth, which is, in this case, very, very small, so say micronsized-sized particles of something that is artificial, metal or grains of materials that we wouldn’t expect to be present in the lunar dust naturally.

FLORA LICHTMAN: So not like a big alien machine.

SOFIA SHEIKH: No, not in this case.

FLORA LICHTMAN: Like the crumbs of a big alien machine.

SOFIA SHEIKH: Yes, exactly.

FLORA LICHTMAN: How long can those kind of remains persist in a moon-like environment, millions of years, billions of years, hundreds of years?

SOFIA SHEIKH: Yeah, the great thing about the moon is that it is a very stable environment in our solar system. So certain planetary environments, especially like the Earth, you have all of these geological processes and atmospheric processes that degrade signs of technology or even just things like surface features over time.

The Moon is great because it doesn’t have very many of these processes. And so if you were to get some sort of artifact or shard of a technology that lands on the Moon, it’s going to stay there for a really long time. And over time, the lunar regolith gets deeper as micrometeorites hit the surface of the Moon.

So over millions, tens of millions, hundreds of millions of years, stuff will get buried by dust. But it’s a really slow process. And other than that, things just kind of hang around.

FLORA LICHTMAN: But what are the chances that those solar panel crumbs or computer dust would end up on our little Moon? How much technology would you need out there for it to likely hit our Moon and then for us to find it?

SOFIA SHEIKH: Yes, the devil’s in the details here. So in order to get enough of a background level of just techno dust floating around out there in space such that you would end up with a couple pieces on the Moon, you would need to start with a lot of technology out there in the galaxy.

In this case, I think, in this proposal, it’s something like 70% to 80% of all stars in the galaxy would have had to have a sphere of solar panels around them, what we would call a Dyson sphere or Dyson swarm. So that’s a pretty extreme proposal. We would need to imagine a civilization that spans the entire galaxy and has technology that we can’t imagine building right now.

But at the same time, bring it back to the Earth analogy. There are many civilizations that have arisen on Earth and had extreme cultural and technological influence during their time. And then time is very long, and much later, traces of that civilization might be a lot harder to find.

So if there had been some sort of galaxy-spanning civilization, we might not see traces of it when we look up into the night sky. But we might see traces of it if there were enough artifacts left behind that one of them might end up on the Moon. Or at least pieces of it might end up on the Moon, I should say.

FLORA LICHTMAN: I know that you’re personally interested in radio signals. That’s your technosignature of choice.

SOFIA SHEIKH: Yes.

FLORA LICHTMAN: And they’re often the go to. What’s the advantage of radio signals?

SOFIA SHEIKH: Well, I’m certainly biased because I’m a radio astronomer. But if you want to send a message across the galaxy, sending it in light is the best way how to do it, the fastest and most efficient way.

But radio waves in particular have their own advantages over other forms of light in that their super low energy, so low cost, very cheap to send your message. And they also aren’t really stopped by gas and dust and other things that are commonly found in the plane of the galaxy, which is a huge advantage.

FLORA LICHTMAN: Do we know what an alien radio signal would look like? Do we know what we’re looking for there?

SOFIA SHEIKH: Yes and no, which is often the answer in this field. We know that we use radio signals all the time on Earth, probably the way that listeners are going to experience this interview. The way that I’m giving this interview all relies on our radio telecommunications.

And so we how to modulate radio signals to pack a bunch of information very efficiently into radio waves. And one way that we do this is by packing a lot of information into a very narrow frequency range, which is called a narrow-band signal. And from an interstellar perspective, narrow-band signals are really great because they don’t look anything like natural signals.

So yes, some stars will give off radio flares, or black holes might give off radio emission. But those kinds of radio waves look nothing like the ones we use to communicate. So when we look out there in the galaxy, we specifically look for kinds of radio waves that seem compressed in some way or information bearing in a way that we don’t expect natural signals to be.

FLORA LICHTMAN: What about the hunt? I mean, is it getting easier to do this kind of searching?

SOFIA SHEIKH: Absolutely. I mean, especially in the last decade or so with the boom in compute technology and receiver technology, we’re able to search billions of frequencies at once, billions of frequency channels. And when this research started in the ’60s, you literally had to do one channel at a time, like physically turning a radio dial.

So the speed at which we’re able to search through space looking for these signals has magnified greatly in the last decade or two. And we’ll continue advancing at that rate and accelerating as we’re applying things like new algorithms and putting new telescopes on sky. So it’s a really exciting time for the field.

FLORA LICHTMAN: Are there other technosignatures beyond machine dust and radio waves?

SOFIA SHEIKH: Yes, there are. Much like biosignatures, where a big part of the field is imagining what life could be like and then imagining the signatures of that life, there’s a lot of modeling and theory work that goes into technosignatures as well. So everything from radio beacons to lasers used to launch lightsails to city lights on a planet that would be visible on its night side to atmospheric pollution from factories, all of these different approaches are different kinds of technosignatures that scientists are thinking about and modeling and looking for.

FLORA LICHTMAN: If we were somewhere else in the universe, could we detect Earth with the tech that we have now?

SOFIA SHEIKH: I love this question, partially because I published a paper on it two years ago. Yes, we could detect ourselves. So Earth could detect Earth in a couple of different ways.

The way that we are most detectable is through our planetary radar. So some of you may know or remember that the largest radar dish that ever existed on the Earth was the Arecibo radio telescope. It hosted the most powerful radar that humans have ever built.

And unfortunately, poor Arecibo collapsed a couple of years back. But when it was active, we used it to identify asteroids that might be in danger of one day impacting the Earth. And to do this, you have to beam really powerful radio waves at the asteroid. And it’ll bounce off the asteroid and come back to Earth, and we measure the reflection.

But some of those waves don’t reflect off the asteroid. They just keep on sailing out into space. And if there were other civilizations doing that with this Earth-level technology, we’d be able to see them halfway across the galaxy, like almost from here to the galactic center.

So in many of our everyday things like cell towers and cell service emissions or GPS or these kinds of everyday technologies, we’re not that detectable, at least to other civilizations like ourselves. But there are some things that we do that will be very clear and obvious, even over interstellar space.

FLORA LICHTMAN: I mean, are there technosignatures that you feel like we haven’t come up with yet because we don’t have that tech?

SOFIA SHEIKH: Absolutely. I mean, this is a big challenge in this kind of work because astronomical timescales are immense. And so we’re sitting here with about 100 years of radio technology. But we don’t know what we’re going to invent in 10 years, much less 100, 1,000, a million years.

And so this is something that really requires some interdisciplinary thinking about, what do we use technology for? What could we imagine using technology for in the future? And what are the physics and engineering limits that we might run up against in trying to apply technology at these huge spatial scales? And only by doing these kinds of exercises can we then think about what kinds of observables might come with that and how we can do astronomy to search for those technologies that maybe we haven’t invented yet here on Earth.

FLORA LICHTMAN: This sounds like an amazingly fun job to me, your job. It’s like science fiction imaginative thinking meets hard science.

SOFIA SHEIKH: Yes. No, I really enjoy that part of it. I get to think about a lot of very different topics on any given day and talk to a lot of really cool collaborators across not just astronomy and physics but also archeology and future studies and fields that I don’t know much about, but I’m always excited to learn more.

FLORA LICHTMAN: That’s fascinating. Doctor Sofia Sheikh is a technosignature research scientist at the SETI Institute. Thanks for joining me today.

SOFIA SHEIKH: You’re very welcome.

[MUSIC PLAYING]

FLORA LICHTMAN: This episode was produced by Charles Bergquist. And just a thought, why not transmit this podcast toward some intelligent life you know about? You know, tell your friends about Science Friday.

I’m Flora Lichtman. Thank you for listening.

Copyright © 2026 Science Friday Initiative. All rights reserved. Science Friday transcripts are produced on a tight deadline by 3Play Media. Fidelity to the original aired/published audio or video file might vary, and text might be updated or amended in the future. For the authoritative record of Science Friday’s programming, please visit the original aired/published recording. For terms of use and more information, visit our policies pages at http://www.sciencefriday.com/about/policies/