Listening for the cosmic ‘dark ages,’ from the lunar far side

The LuSEE-Night mission would place a small radio telescope on the far side of the moon to listen for signals of the cosmic "dark ages."

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:03Ira Flatow?

  Hi, I'm Ira Flatow, and you're listening to Science Friday. In early April, all eyes were on the moon, right? With the lunar flyby of the Artemis space mission, and they got an unprecedented view of the lunar far side. But researchers are working to put eyes on the far side of the moon in another way, by delivering a tiny radio telescope there. It's called Lucy Night, and joining me to talk about it is Anja Slusar, science lead for the mission. Welcome to Science Friday.

• 0:34Speaker 01

  Hello, thank you very much.

• 0:36Ira Flatow?

  Anja, describe this little radio telescope for me, if you will.

• 0:40Speaker 01

  Okay, so we're putting like a small Pathfinder radio telescope called Lucy Night on the lunar far side. And really, it's a Pathfinder, it's the simplest thing you can imagine that could receive radio signals from the outer space. So people have been dreaming about putting radio telescope on the moon, because moon has this special property, then on the far side of the moon, you're at the same time shielded from the earth and shielded from the sun, and that's supposed to make it one of the best observatories for the radio frequency observations in the entire solar system. Okay? And especially so at the very low frequencies, where basically observations from the ground are very, very difficult. If you go below 50 megahertz, observations from the ground, basically, it's like looking

• 1:24Speaker 01

  up from the bottom of the swimming pool, everything is blurred, it's a total mess.

• 1:29Ira Flatow?

  So I should not be picturing this big, giant, Aracibo-type radio dish? We're talking about a demonstration project, a little project, right?

• 1:38Speaker 01

  Yeah, it's a little project. It's basically, calling a telescope, in some sense, it's a misnomer, right? It is essentially four antennas, the four stick antennas like your portable radio, it's really more kind of radio receiver. It's like FM receiver you have at home, but kind of slightly, at slightly lower frequency, and can kind of see all the frequencies at the same time. So it will make, it will make very, very blurry pictures of the sky, that we can then reconstruct to then turn into kind of like a low-resolution map of how the sky looks like at these frequencies. However, having said that, it will be the first time in the history of humanity we're actually able to make any maps at this very, very low frequency.

• 2:18Ira Flatow?

  Now, there's been talk that it can see something called the Dark Ages signal. What is that?

• 2:26Speaker 01

  Yeah, so Dark Ages signal, it's something very exciting. I would call it like a platonic ideal or something where the field is going towards, something they want to see in, I would say, 50 years. So Luc tonight will not see it, but it's a pathfinder for seeing Dark Ages, okay? So Dark Ages refers to this particular epoch in the Evolution Universe, where kind of this initial hot plasma, this soup of protons, electrons and so on, has kind of cooled down enough that we have just neutral hydrogen and nothing more. And because it's so early that we have no stars, no stars have already turned on. This is a very, very pristine universe, right?

• 3:08Speaker 01

  Which we can explain just using fundamental physics like general relativity, atomic physics, thermodynamics, stuff like that. We can make extremely precise predictions. Because once the stars turn on and you get galaxies and planets and so on, universe becomes a very complicated place. It's like weather. But before it starts to on, if you could measure that, that epoch, you could really make some really fundamental measurements of the universe. Now, unfortunately, as I said, Luc tonight will not see Dark Ages, because they are kind of foregrounds, which are much brighter than this thing, from our own galaxy and other galaxies shining. But it will kind of enable us to basically demonstrate that far side of the moon is really as good as a place to make observations that people think it is, right?

• 3:52Speaker 01

  People have been thinking it's the best place to make these measurements, but nobody has actually done.

• 3:56Ira Flatow?

  Is this sort of seen as a way to pave the way for future radio telescopes on the far side of the moon?

• 4:03Speaker 01

  For sure, for sure. Basically, Luc tonight, it's a pathfinder and we're really thinking about where to go next. And the natural way is to build up so-called interferometers, where you kind of put many individual elements of a radio telescope and kind of combine those signals, so they start acting like a big dish. However, you know, you eat elephant in small pieces, so that's why we start with a small pathfinder. And if it works, you will learn a lot about how to make these observations, how to survive the lunar night, how to operate the telescope, what the big problems are. There's still fundamental unknowns, like, you know, maybe they're micrometrites, maybe...

• 4:42Speaker 01

  Moon has like weak ionosphere that is going to make our duration difficult. You know, Lucy Night will kind of try to understand and thus pave the way for bigger instruments in the future.

• 4:53Ira Flatow?

  Are you hoping to be able to see these dark age signals or not?

• 4:57Speaker 01

  With Lucy Night, I don't think we'll be able to see dark age, a dark age signal unless something really surprising happens. Having said that, because this is such an unexplored part of the radio frequency spectrum, maybe there will be other surprises, you know? There are people who think maybe because of my career background is very bright at these very low frequencies. Maybe there is new dark matter physics or some new other fundamental physics that will produce kind of interesting new spectral lines or features in the maps or in frequency space. You know, there are very, very, very few parts of modern science where kind of things are unknown at this level of precision. Okay, so that's what makes it exciting.

• 5:40Ira Flatow?

  That is sounding exciting. So how do you get to the far side of the moon?

• 5:45Speaker 01

  So we get to the far side of the moon on board of a lander which is paid by CLIPS. CLIPS is the NASA Commercial Lunar Payload Services. Basically, it's a way for NASA to develop like an ecosystem of private sector providers that can take you to the moon and land you there. And basically we have like DHL to the moon and we are one of the early landers from this program. We will be on the Blue Ghost 2. You might remember a Blue Ghost 1 successfully landed on the lunar near side last year. It was the first successful landing by a private sector company on the moon.

• 6:24Speaker 01

  And that's why it makes us very, very hopeful because we will be essentially using the same lander, but on the lunar far side. Landing is essentially autonomous, so in principle it's not that difficult whether you're on this side or the other side. One thing is that because you're outside of the rect field of view from the ground, you have to rely on the relay satellite that kind of bounces the signals from the earth, so you can actually communicate back to earth. And this adds clearly a layer of complexity, but we'll see. Fingers crossed we land and our instrument works.

• 6:57Ira Flatow?

  And what's the timeline on this?

• 7:00Speaker 01

  So we're still talking about launch being slated for the end of 2026. It might get delayed, nobody knows, like in space business, things often get delayed. But I think, no, I can't wait to get there and see.

• 7:16Ira Flatow?

  Well, the Chinese were the first to land a vessel on the far side and return samples. You're looking to be the first to put a telescope there.

• 7:25Speaker 01

  Yeah, and it will, so there will be many, many firsts in this mission. It will be the first US mission to land on the far side. It was first private sector mission to land on the far side. It will be the first functioning radio telescopes on the far side. Chinese also had like an instrument that unfortunately didn't work very well. And we're trying to kind of not repeat similar mistakes. It will be the first commercial instrument trying to survive the lunar night, which is very difficult, right? So moon is extremely difficult to survive both the day and night because during the day it's very, very hot. And during the night it's very, very cold. And so you have to design for two very different thermal environments.

• 8:05Ira Flatow?

  Well, I have a, I have a practical question for you. If, if it's on the far side of the moon and the moon is always facing away from the earth, how do you get your signals back to earth?

• 8:16Speaker 01

  So there is a satellite that circles around the moon. And if it's far away, it can be simultaneously in the view of your instrument, the far side and the earth. But mostly, it basically, when it's on the far side, it talks to our Lucy night. And when it goes around, it talks to the ground. And this kind of allows us to kind of transfer our data back, right? But this, for example, puts like an interesting level complexity because the total amount of volume you can, you can transfer, it's quite low. We hope to transfer about six gigabytes of data for every lunar cycle, 28 days. And so one could almost email this data.

• 9:02Ira Flatow?

  I'm fascinated about how you got this idea. How did this project get started? Where did the idea come from?

• 9:09Speaker 01

  This is a very interesting project. I started about six or seven years ago. And it went from the top level of echelons of the institutions,

• 9:22Speaker 01

  trying to get DOE and NASA to work together for various reasons that are kind of lost in the midst of time. But it was like, at some point, essentially, I received a call asking me, do you want to take part in a project to put radio telescopes on the moon? And I said, why not? Like, this sounds like a very exciting opportunity.

• 9:44Ira Flatow?

  So they just called you up and said, we've got a spot for you to put your project on? You want to go?

• 9:51Speaker 01

  Yeah, well, there was no project time. People just said, do you think interesting science could be had by putting radio telescopes on the lunar far side? And at the time, we were kind of thinking about putting a large telescope on the ground for kind of related science.

• 10:07Speaker 01

  But this sounded like there was fun thing. And basically, there was a spot and it's time to go. So I said, yes. And I never thought I would be doing like a space mission in my life. But this is how science goes.

• 10:20Ira Flatow?

  Are there other astronomers who are annoyed that you got to skip to the front of the line?

• 10:26Speaker 01

  I mean, partly, yes. Because normally, this project starts with the community processes. You know, these big surveys where kind of community comes together and decide what are the next big step. So if you want to kind of start a new project, you have to start kind of going around, your colleagues lobbying, trying to convince them why they should be doing something. And this takes time and effort. And while this was kind of came out of nowhere. But frankly speaking, it's also a kind of relatively small project, right? It's not like big flagship projects that DOE often does. For me personally, the fact that it's small, it's been kind of really like a boon. I feel like a postdoc again. Like, it's such a simple system. I can understand everything and I can go and

• 11:10Speaker 01

  and really kind of like develop low-level things without having to fight bureaucracy. But having said that, for somebody who has spent their career doing stuff on the ground, like the psychology of sending something to the moon is just... You're just insane, right? It's just very difficult, this idea. Now you're done, you're going to put it in the box, and you're not allowed to touch it anymore. And if you messed up, well, you messed up. It's too late now, right? That's been new and very, very difficult.

• 11:40Ira Flatow?

  Well, you're the pioneer. You're the pioneer in this, right?

• 11:44Speaker 01

  We're the pioneers.

• 11:45Ira Flatow?

  Well, I wish you great luck. And please stay in touch because we'd like to know when this blasts off and we'll keep track of it, okay?

• 11:52Speaker 01

  Okay, thank you very much for having me.

• 11:54Ira Flatow?

  You're welcome. Anjesh Slosar is science lead for the Lucy Knight Project. He's based at Brookhaven National Laboratory out there on Long Island. Thanks for listening. And you know, we're always looking for your ideas. Give us a call on the listener line, 877-4-CY-FRY. That's 877, number 4, CY-FRY. This episode was produced by Charles Berquist. I'm Ira Flatow. We'll see you soon.