The Kaguya-hime Hypothesis

Kaguya-hime I

There’s an old children’s story that my mom used to tell me, as she brushed my hair and tucked me under the covers. It starts like all Japanese monogatari do: Long, long ago…

There was an old bamboo farmer who lived with his wife; a childless couple. One day, as the man went about working in the bamboo forest, he stumbled on a glowing bamboo stalk. When he cut it open, he was shocked to find a little girl sitting inside, about the size of a thumb. The old man took her home, where his wife was delighted that their prayers for a child had finally been answered. The couple named the girl “Kaguya-hime” (Princess Kaguya), and took her in as their own. Curiously, ever since Kaguya-hime arrived, the bamboo cutter kept finding gold in his bamboo. Suspecting that their child was sent from the heavens, the old farmer resolved to raise Kaguya-hime like a princess and built a large mansion for his family with his newfound wealth.

Kaguya-hime led a blissful childhood and quickly grew into a beautiful young woman. In fact, she seemed to emit a soft glow, all the more convincing her parents that she was some sort of heavenly being. News of her beauty spread throughout the country, despite her parents trying to hide her away. Many suitors clamored for her hand, but Kaguya-hime would hear none of it. She didn’t want to get married. She didn’t want to be owned.

Eventually, five of the most persistent men persuaded the couple to have Kaguya-hime choose between them. The couple caved, fretting over their old age and wanting someone to take care of their precious daughter once they were gone. So, Kaguya-hime came up with five impossible objects for each suitor to retrieve, declaring that she would marry whoever successfully completed their task first.

She directed the first suitor to get the Buddha’s stone begging bowl from India. The suitor, a relatively conniving man, deduced that this task was unfeasible and decided to create a fake bowl instead. However, Kaguya-hime coldly exposed his deception when he presented his gift, proclaiming that the real bowl would have glowed with holy light. Shame-faced, Suitor #1 scurried out of the family’s house.

The second item was an ornate tree branch from Horai, a mythical island. The tree was rumored to be made of gold and silver, bearing white jewels. Of course, since the island didn’t actually exist, Suitor #2 contracted the country’s top six jewelers to recreate the branch. Even Kaguya-hime was stumped when the nobleman proudly bestowed his gift, as the man had made up an intricate cover story detailing his journey to Horai. Luckily, the disgruntled jewelers came knocking to her house just in time, demanding the noble fulfill his outstanding payment to them, hence revealing his con. And so, this suitor was out of the race as well.

Suitor #3 was asked to bring a robe made out of skin from China’s legendary “fire-rats.” Using his connections, he found a merchant from China claiming to have the robe, and paid an enormous sum of money for it. Unfortunately, honest as this suitor was, he was a bit gullible, too. The fire-rats were said to be fireproof, but the suitor’s gift quickly crumbled into ashes when Kaguya-hime held it over fire, revealing it as a fake. The saddened man left Kaguya-hime, still single and with a significantly lighter wallet.

The fourth gift requested was a brilliant, multi-colored gem taken from a sea dragon’s neck. Suitor #4 set out to sail with a few of his men, but quickly got swept into a terrible storm. After a stomach-churning few days, he and his crew escaped with their lives barely intact. Rather than continue to risk his life, Suitor #4 decided to give up and stop pursuing Kaguya-hime.

The last suitor, #5 – though more upstanding than the rest – was given the unenviable task of finding a swallow that carries a cowry shell in its stomach. Searching far and wide, the man finally found a nest with the swallow, but when he tried to climb up to it, he fell from a great height. The suitor was severely injured in his attempt and abashed by failing the quest. He couldn’t bring himself to face Kaguya-hime ever again.

With the suitors taken care of one way or another, Kaguya-hime thought she was in the clear. However, rumors of her beauty reached even the Emperor’s ears, who decided to visit her from the capitol. When he finally saw Kaguya-hime in person, the Emperor was enraptured, asking for her hand in marriage and promising to give her anything she wanted. The Emperor was a powerful man, so Kaguya-hime couldn’t give him a made-up quest like the rest of her suitors. However, she was still adamant in rejecting his proposal. She told the Emperor that she wasn’t from Earth and wouldn’t be able to stay with him. Naturally, the Emperor didn’t believe her, but he accepted her reasoning graciously. She promised to stay in touch through letters, and they exchanged poems back-and-forth over the next few years, as she continued to live happily in her parents’ cottage.

One summer, her parents noticed that Kaguya-hime weeped whenever she looked up at the night sky. As they questioned her, she crumbled and revealed the truth – she wasn’t from Earth, she was from the moon. Her time on Earth was almost up, and her people were coming to retrieve her on the next Harvest Moon.

Her parents were horrified hearing this, and scrambled for some way to keep their daughter on Earth. They even enlisted the Emperor’s assistance, who agreed to lend as much of his earthly might as he could. On the day of Kaguya-hime’s return to the moon, the Emperor sent thousands of his guards to the bamboo farmer’s house. A thousand archers were stationed on the roof of Kaguya-hime’s estate to shoot down any heavenly envoys. Another thousand were placed around all the entrances, blocking the way to Kaguya-hime, who was hidden in one of the innermost rooms with her parents.

But it was all for naught. When the beings descended from the moon, everyone was blinded by a strong light and dropped all their weapons. Kaguya-hime was compelled to come outside. She bid her parents a sad goodbye, thanking them for raising her for so many years. A heavenly robe was placed on her shoulders, and she re-joined her people, leaving her life on Earth behind. Her parents remained on the ground, tearfully watching their daughter ascend to the moon, where she belonged.

I loved this story when I was younger. There are no clear morals, at least not like Aesop’s fables. But I was fascinated by this beautiful moon princess, who left everything she knew on Earth behind. I would gaze up at the night sky, wondering if Kaguya-hime was lonely on the moon, and ask my mom, distraught, whether Kaguya-hime ever got homesick. Coincidentally, this was around when I first discovered the concept of homesickness, from sleepaway camps and sleepovers.

Now, though, as I live life in my purported home-away-from-home at Penn (the homesickness is bound to fade eventually, right?), I wonder what “home” even was for Kaguya-hime. The Earth or the Moon? The tale feels unfinished. Surely Kaguya-hime’s life didn’t end when she returned to her rightful place on the moon. In fact, it had probably just begun.

Maybe that’s why I can’t seem to shake this idea from the grip it has on me: what could life have been like for Kaguya-hime after the fable, living on the moon?


I’m nothing if not a scholar (or at least that’s what my resume says), so I should approach this question rationally, as expected of a fourth year student at an esteemed Ivy League institution. Before I can start dreaming up how Kaguya-hime would have lived on the moon, I need to understand what the biggest differences would be from living on Earth.

The most obvious change between here and there is much weaker gravity. Physics was never my strong suit, but even I know Earth’s gravitational pull at the drop of a hat: 9.81 m/s². The moon’s gravity stands at 1.62 m/s², around 1/6th of ours. That means I weigh about 20 pounds on the moon. I try to imagine weighing the same as my dog, but it’s hard to wrap my mind around, since I regularly hoist my dog onto my hip as I walk around my house.

There’s also the lack of an atmosphere. Here on Earth, our multi-layer atmosphere protects us from a myriad of extraterrestrial threats—UV radiation, meteors, extreme temperature fluctuations, you name it. Its composition is optimal to support life, with 78% nitrogen, 21% oxygen, and other gases like argon. Quite literally, it’s why we breathe every day. But the moon’s atmosphere is thin and weak, unable to block out the sun’s rays or meteoroids. Weak gravity is partly the culprit: the moon can’t hold onto its own gases. The atmosphere is so thin that it’s technically called an exosphere. A few different elements have been discovered in the exosphere, familiar ones like argon, helium, oxygen, and greenhouse gases. Still, it’s nothing like our ~10,000 km thick atmosphere, and definitely not conducive to breathing, so get your space suits ready.

Along with the exosphere, the moon’s weak magnetic field makes cosmic radiation a major problem. When China’s Chang’e-4 mission landed on the far side of the Moon (for the first time ever!) in 2019, they found radiation levels over 200 times what we experience on Earth. NASA found these levels okay for the length of moon exploration missions that are currently being planned. But for permanent habitants, like Kaguya-hime and her moon people, they would need permanent protection from these cell-killing rays. On the flipside, this means they’d never get to feel direct sunlight. Utterly vampiric. Somehow, sunlight would need to be stimulated, else they suffer from a dearth of vitamin D.

Lunar soil, known as regolith, is very different from the brown, nutrient-rich dirt we play in as kids. Food would have to be grown very differently. We also take it for granted that we can turn the tap on and drink clean water. No such luck on the moon. China’s Chang’e-5 mission did discover a hydrous mineral (NH₄)MgCl₃(H₂O)₆ in the lunar soil it returned, showing that water can exist on some parts of the sunlit moon. But it still needs to be excavated and processed somehow, and there’s no telling how rare the minerals are. I’m feeling parched just writing this.

Thankfully, food apparently shouldn’t be a big issue – there are many ways to grow plants and generate lab meat, as demonstrated by the abundance of experiments currently being done on Earth using soil that mimics lunar dirt to successfully grow food. NASA has also made progress on the oxygen front, testing robots capable of harvesting oxygen from regolith.

That was a lot – let me summarize. It boils down to food, water, shelter, and air: the four basic needs we’re taught from a young age. To offer a compelling case for how Kaguya-hime could live on the moon, these are the main factors that I need to figure out. But where to start? The latent architecture interest that I nursed when I was younger prods at me (back when I wanted to be just like Annabeth Chase, daughter of Athena). Building design would undoubtedly be vital in creating hospitable physical environments on the moon.

I need to find myself a moon architect.

The Interview

Takaharu Igarashi, PhD candidate at Purdue VRSS (Value through Reliability, Safety, and Sustainability) Lab. That’s a bit of a mouthful. I stumble across Takaharu’s portfolio while reading Will Dowd’s newsletter, The Lunar Dispatch, and immediately get intrigued by the Resilient Lunar Habitat System that he designed back in 2019. My LinkedIn stalking paints him as a straitlaced scientist, but the “Space Architecture” in his bio catches my eye. I have nothing to lose, so I fill out the contact form on his website. (I knew the cold emailing skills I polished during recruiting would come in handy someday, for a real cause.)

I decide to leave out the part about Kaguya-hime for now, lest he thinks I’m too out there. To my pleasant surprise, just a few days later, I get a response and we set up an hour to chat on a Saturday morning.

During my pre-interview research on plausible moon habitats, there are a few competing hypotheses: one is the sort of sleek white lunar colony we’re used to seeing in movies. To make these, the European Moon Village Project by the European Space Agency (ESA) proposed launching inflatable modules on the moon surface to then be covered by robots that 3D print lunar regolith blocks. Basically a moon igloo.


 Design: SOM, in collaboration with the ESA

Another option is to use the existing, vast lava tunnels under the moon’s surface. These offer natural protection from the harsh temperature, radiation, meteorites, etc. It sounds dystopian, living underground, but Takaharu seems to fall into this belief camp. And I can see the appeal, in an almost Neanderthal-way. It’s easy to love his mockups of “cave dwellings” with its heaven-looking skylights.


Design: Takaharu Igarashi

Either way, regolith seems to be the lunar panacea, with its ability to block out cosmic rays and protect human habitants, and even to make solar panels, and, well, everything.

I try to think of smooth ways to present the premise of my story to Takaharu. Like, there’s this story of a moon princess in Japan, and I want to ask you about how she would have lived on the moon even though it’s obviously just a fable, and…fuck it, I’ll just tell him straight-up.

The fateful Saturday rolls around. It’s a warm day, sunny and bright and fully at odds with the nerves settling in the pit of my stomach. I happen to be home home for the weekend, so I settle into my usual “important call” spot in my dad’s basement office, surrounded by mementos of my childhood. I don’t know why I’m so nervous. Half of my mind is stuck in fairytale-land, the other in lunar science mode. I ping-pong between the two, trying to make sense of it all. Reconciling my ideas suddenly feels like a more monumental task than it should.

I start my Zoom and notice my camera isn’t working. It’s just showing a green screen. Shit, shit, shit. Unfortunately, he’s punctual, joining my Waiting Room at 2pm ET on the dot. There’s no time to restart my laptop. I keep toggling around with the camera, but he joins with his video off, warning me that his 3-month-old might start crying during the call. Ok, phew, no need for video then.

I’ve prepared a whole plan for the interview, but things quickly go awry.

First, I try to get us on the same page. Has he ever heard of the story of Kaguya-hime? A slow yes. He’s from Japan, so yes. I rush to explain that I’m half-Japanese and grew up listening to the tale, too. It’s hard to gauge his reaction when I can’t see his face, so I keep rambling.

“I know it sounds a bit absurd, but my idea for the story about lunar modules came from wondering how a modern-day Kaguyahime would live on the moon. If you can humor me, I want to conduct this interview as though we’re speculating about that tale, and how she would have lived on the moon after her life on Earth…”

He sounds bemused, but agrees to play along.

Oh wait, backtrack, backtrack. I forgot to ask for his intro.

“How did you get interested in space architecture?”

Takaharu explains that since childhood, he liked drawing and found space fascinating. He happened to choose architecture as his undergrad & master’s degrees, but his interest in space nagged at him. So he decided to add an aerospace background to his education.

“To do anything new, you need to have the basics down,” he emphasizes.

I nod along (although he can’t see me), like a student listening to her professor. He makes it sound so simple – he needed to understand both hardcore engineering and architecture to pursue his dreams, so that’s what he did.

I can’t help asking: “What do you want to do with this education? What exactly is your dream job?”

Without hesitation, he responds, “Space architect.”

He caveats that the job doesn’t have a solid definition right now, but he believes the profession will gradually solidify. He wants to do both the dreaming/concept making/designing and the actual implementation – his passion is obvious. Living in space is his dream job. My intrusive thought is whether he would leave his family behind to do so (Interstellar-style), but that feels rude to ask when his young daughter is literally in his arms. Still, I can’t help but admire Takaharu. What must it feel like to know exactly what you want to do in life, and to have the conviction to carve out that path yourself?

Back to the topic at hand. I mention one last assumption. For the purposes of this interview, let’s say Kaguya-hime and her moon people have the same biology as humans. He laughs, agreeing that’s an important point: “If we’re talking about a different set of biology, that would be a completely different discussion.”

The foundation of any good fairytale is the setting, so I start there.

“Where would Kaguya-hime and her people have lived?”

The obvious choice is to live underground, using natural structures already on the moon. They could build aluminum modules, like the International Space Station (ISS), within preexisting lava tunnels. But a big issue with the lava tubes would be their integrity. The moon has “moonquakes,” and we don’t know how solid the tunnels are yet. Geostructural surveys need to be done. A cave-in would be much more disastrous than living on the surface and being exposed to high levels of radiation.

And there are some construction hazards. Crane-like equipment would probably be used to lower and raise things during construction. But sub-gravity is not zero gravity. Six tons may feel like one ton on the moon, but that’s still as heavy as an elephant. Besides, mass doesn’t change, so the force needed to stop any heavy things falling stays the same.

I bring up the design I saw from the European Moon Village, with the inflatable modules and 3D printed regolith blocks. Takaharu hums thoughtfully. Kaguya-hime could live on the surface, but it’s a lot harder than it sounds to protect on-the-surface structures with regolith. Apparently, 3D printing lunar blocks would only work if a substantial amount of lunar soil can be dug up, and we don’t know how much we can actually dig on the surface. Extraterrestrial soil tends to be pretty rockhard – even the Martian rovers had a lot of trouble digging up their soil. Basically, finding already extant lava tubes would come earlier than figuring out how to dig regolith up and run it through a chemical process to create enough building blocks.

Inspiration strikes Takaharu as we talk.

“It’s possible that the inflatable modules could be put directly into the lava tubes instead to create habitats, a hybrid of the two ideas.”

What if the underground habitat that Takaharu designed was used for Kaguya-hime and her people, instead of the half-year mission he designed it for? How could the design be expanded to accommodate a permanent colony? Again, lava tubes hold the answer. If built in the proper location, the tunnels could connect houses underground as part of a network, which would be a lot easier than plowing more regolith. However, similar to living on Earth, Takaharu says there’s probably not a perfect place to settle. The Artemis program is looking at settling on the South Pole, but that’s a pretty flat surface. Lava tubes have been found mainly near the moon equator, but it depends on how many tubes can actually accommodate people. Strong geographical features are ideal, since hills or mountains can shield from harsher climates.

I hear Takaharu set his phone down for a second, switching his daughter to his other arm. There’s a pregnant pause over Zoom. I have a premonition that he’s about to say something insightful.

“You know, if this were a civilization with a longer history, you would probably see a combination of houses aboveground and underground. Maybe rich people would live deeper underground.”

I like where his thinking is going.

We discuss how more marginalized people would probably live on the surface with thinner regolith layers, because it would be much more dangerous there. He says that marginalized people always emerge in society, unless the “moon people” somehow have very different psychological and social behaviors than humans on Earth. It’s a sobering thought – some things never change.

And for there to be the oppressed, there must also be the oppressors. The ultra-rich. In the moon’s case, water would likely be the key to power, treated as something close to a rare metal.

Since the Chang’e-5 mission successfully found hydrous minerals in regolith, Takaharu envisions water excavation being combined with digging up regolith for building materials. But there would still be quite a limited supply. A moon colony would need some shipping of fresh water from Earth, so whoever controls imports and exports would get rich. He asks if I’ve seen or read Dune. I confirm. Wiki-watching counts, right? He likens the situation to Arrakis (which I later learn is the planet in Dune that controls melange, an uber important resource). Those who control water would have enormous power on the moon – even more so than people who control food and air.

One has to wonder where Kaguya-hime would have fallen on this social ladder. I find it hard to picture the beloved “princess” as a poor member of lunar society. If anything, given her otherworldly beauty, Kaguya-hime would probably be the moon world’s equivalent of a supermodel. Or maybe even a nepo baby from a water tycoon family.

Even for the upper class, though, life on the moon wouldn’t be perfect. I ask Takaharu if Kaguya-hime’s people could go outside. Would they have to wear spacesuits all the time? His answer: it depends. If spacesuits were light enough, there could maybe be living areas somewhere “in-between” indoors and outdoors. But with today’s technology, people on the moon would have to rely on conventional airlocks to pressurize/depressurize and clean themselves off before going from outdoors to indoors. I hold back a giggle as an image pops up in my head, unbidden, of Kaguya-hime wearing her traditional, multi-layered Japanese kimono stuffed into a skintight spacesuit. My smile vanishes quickly when I remember that I can barely get through a few hours in a kimono without feeling claustrophobic. Kaguya-hime would feel the same in a spacesuit, itching to be free.

I ask if they can only go outside during lunar mornings (~14 Earth days), since lunar nights (also ~14 Earth days) are essentially a deep freeze. Takaharu corrects me. Actually, they would basically need to stay inside all the time, since temperatures get boiling hot in the daytime. He likens it to life in Antarctica or the Sahara. I shudder. Imagine the cabin fever. The isolation. I feel sorry for Kaguya-hime, who definitely got used to Japan’s mild weather and feeling the wind directly on her skin; who suddenly found herself back to coping with the moon’s extreme temperatures, restricted in her daily movements.

Another thought nags at me. If the lunar day/night cycle is basically two weeks in bright light and two weeks in complete darkness, would the moon people’s circadian rhythms reset over time? Would the habitats need some sort of mechanism to indicate day/night Earth cycles? Takaharu sounds taken aback – for our circadian rhythm to shift, we would basically need to evolve into a new species, which would take many millenia. In the absence of such evolution, his answer is yes. Moon habitats would probably have an interior mechanism to keep a regular circadian cycle, along with those sunlight simulators I mentioned before. Kaguya-hime might have two clocks in her room, one to tell “moon time” and one to tell “Earth time.”

In the presence of such evolution? That question brings us back to our initial assumption, that the moon people have the same biology as us Homo sapiens. If we remove that constraint, it’s entirely possible that Kaguya-hime and her people have already evolved a new circadian rhythm. At the risk of creeping into pseudo-science, if we settle on the moon (or really, anywhere that isn’t Earth), we would probably see a shift in physiological features over time. It’s hard to tell what exactly the changes would be, though. For example, over many generations, adapting to the reduced stress from lower gravity might lead to taller and lighter-framed individuals. On the other hand, stronger bones might provide better mobility and functionality on the moon, in which case a lunar population might evolve to be shorter but strong-boned. Either way, long-term adaptation to the moon is another (maybe more) plausible explanation for Kaguya-hime and her people’s way of living. Maybe that’s why Kaguya-hime’s suitors were so irresistibly drawn to her; she was so unique because she was literally a different species. Takaharu adds that, after her muscles adjust back to the microgravity on the moon, Kaguya-hime would need to undergo intense training if she ever wanted to return to Earth. If she wanted to. Would she?

The moon was once exalted as the ultimate goal for mankind. “We choose to go to the moon” was embedded in every American’s consciousness in the 1960s; a nation, united, pushing the bounds of what’s possible. It was absurd – launch a man into space, land him on the moon, and bring him back alive. Laughable. Impossible. And, yet, despite conspiracy theorists claiming otherwise, it happened. The whole world held its breath on July 20, 1969, watching Apollo 11’s moon landing live. One small step for man, you know how it goes.

But, the novelty soon wore off. NASA’s marketing faded, and with it went public interest. I wonder if the moon was lonely up there, in that 50-year period when she was gone from the limelight.

Now, though, she’s making a comeback. Back off, Apollo. It’s Artemis’ turn to shine.

The name of the Artemis program is apt, if a little too on-the-nose. With these missions, NASA is aiming to land “the first woman and first person of color” on the moon. But as I read through the mission plans, I’m thrown off by the commercial tone it takes. The NASA website jabbers on about enabling a lunar economy, fueling new industries and job growth. No wonder this is the first time in three decades that a plan to return to the Moon has been supported by two presidents in a row. It’s not just about inspiring the nation or advancing science. The private industry, the government, and the military all want a piece of the moonpie.

Part of me bristles at this. Is it naive to want to preserve pure exploration as a motive? I guess the first “space race” was also in the midst of a major political storm. Maybe we’ve never actually done anything just for the sake of doing it. There always has to be people who win and people who lose. Like NASA awarding ICON—an advanced construction technology company known for 3D technology—a $50+ million contract to develop technologies that enable building infrastructure on the moon, from habitats to roads. Or startups clamoring to collect lunar resources. We’re seeing burgeoning water tycoons already. Takaharu speculates that a more permanent Moon state would inevitably get wrapped up into politics, given its likely reliance on “Earth countries” with stable resources to trade. Plus, the US created the Artemis Accords in 2020, a “set of principles for responsible lunar exploration and development.” I.e., the ground rules for exploitation of space resources. Thirty-two countries have signed it so far. India signing earlier this year was hailed as a sign of the country solidifying ties with the US over our proclaimed space race with China.

It all feels so inane. Kaguya-hime’s face swims into my mind, baffled by the spaceships and governments clamoring for a piece of her home. I doubt she would want to be used as a political pawn. But far be it from me, self-appointed defender of the moon, to judge. It just must be so tiring to be the moon, adored and used, over and over.

I want to keep Kaguya-hime’s world untouched.

This all started with a fable I loved as a kid, that my mother read to me at night, with the moon rotating outside my bedroom window.

It’s an impressively enduring tale: of filialness and family, of not quite belonging on this planet. I don’t know why, at the ripe age of 21, it also makes me want to cry a little.

Here is another version of the story – my version.

There once was a precious little girl named Kaguya-hime, born to an older couple, 7 years into a marriage. Somewhat of a miracle and nothing short of a princess, she’s doted on for many blissful years, living in the cocoon that is suburban Northern Virginia.

Eventually, she grows into a beautiful young woman. Suitors come and go (thumb-sucking boys, really), but she’ll have none of it. If she can, she wants to live with her parents and dog forever, in their blissful family unit. Her parents are more pragmatic, of course. There’s an unspoken, anxious need for them to see her safely and happily married before they die. At Kaguya-hime’s sullen proclamation that she’s never getting married or having children, her mom chides, “But who’s going to take care of you when we’re gone?”

Time, cruel as she is, flies by. As Kaguya-hime becomes older, something restless tugs at her – a need to leave, to be something bigger. Although she knows it’s time to go, she weeps every time she thinks of having to leave her beloved parents and home behind.

On the day of her departure, she frets over her parents’ emerging wrinkles and gray hairs, wondering when they got so old. Hugging them tightly, she thanks them for all they’ve done. Tears blur the edge of Kaguya-hime’s vision, but she holds her head high as she walks away to her new life. Her parents watch her go silently, proud and accepting and devastated all at once.

As expected, their world feels a little emptier without Kaguya-hime, a little colder. But their moon is still there, even when they can’t see her. And when they gaze up at night, she looks back.

She always looks back.