Astrum Space - NASA's Stunning Discovery on Pluto's Largest Moon

Episode Date: November 20, 2025

Everything you need to know about Pluto’s shadow, Charon. Join us as we journey to the solar system's frozen edge to explore Pluto’s mysterious companion, Charon. Forming half of the solar system’s most intriguing binary, Charon’s dark surface bears the scars of a violent past, and a bizarre red stain on its pole. Join us to explore everything we know about Charon, the moon that helped to redefine what it means to be a planet.▀▀▀▀▀▀If you love learning about science as much as I do, head to http://brilliant.org/astrum to start for free. You'll also receive 20% off a premium annual subscription, giving you unlimited access to everything on Brilliant.▀▀▀▀▀▀Astrum's newsletter has launched! Want to know what's happening in space? Sign up here: ⁠https://astrumspace.kit.com⁠A huge thanks to our Patreons who help make these videos possible. Sign-up here: ⁠https://bit.ly/4aiJZNF

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It matters where you stay. Hilton, for the stay. At the frozen edge of our solar system, nearly 6 billion kilometers from the sun, a tiny world of ice and rock traces a lonely path through the darkness. For decades, we knew it only as a faint point of love. light, the ninth and most mysterious planet, Pluto.

But this world was not alone. It held a secret, a ghost that haunted our earliest images, a flaw in our photographs that once understood would not only reveal a companion world, but would also shatter our understanding of what it means to be a planet and a moon. This is the story of a world discovered by accident. a world that cracked itself open from the inside out, a world that wears a mysterious red stain gifted from its larger twin. This is the story of Karen. I'm Alex McColligan and you're watching Astrom. Join me today as we journey to the Solar System's greatest double act and uncover the

violent, frozen, and deeply interconnected history of Pluto's shadow self. The story of Karen begins not with a deliberate surge, but with a mistake. On the 22nd of June, 1978, James Christie, an astronomer at the US Naval Observatory, was performing a routine but tedious task, examining photographic plates of Pluto to refine calculations of its orbit around the sun. The images, taken with the 1.5-meter Kaj Strand telescope in Arizona, were not considered high quality. In fact, several plates had been marked as poor or defective because they showed Pluto not as a clean, sharp dot, but as a strangely elongated blob with a distinct bulge on one side. To most, this would have been an annoyance, an imperfection to be discarded. Atmospheric turbulence or improper telescope

alignment could easily cause such distortions. But Christie had a specific background that prepared him to see something others had missed. He spent years photographing double stars, and his trained eye recognized a familiar pattern in the strange bulge. He noticed a critical detail. While Pluto's image was smeared, the distant background stars on the very same plates were perfect, sharp points of light. If the problem were with telescope or the atmosphere, everything in the image would be distorted. The fact that, only Pluto was affected meant the bulge had to be real. There was something else there. Christy began a deep dive into the observatory's archives, unearthing plates of Pluto from as far back

as 1965. Many of these two had been dismissed as flawed, bearing notes like Pluto image elongated. But now these failures became the key to confirmation. Christy saw that the bulge system dramatically moved around Pluto over time. He and his colleague, Robert Harrington, meticulously tracked its position across the years of archived images. They calculated that the bulge circled Pluto once every 6.4 days, a significant number, because it perfectly matched Pluto's own known rotation period. This was the final piece of the puzzle.

The ghost on the photographic plate was a massive companion. A moon locked in a synchronous dance with its parent world. With the discovery confirmed, the new moon was provisionally designated S-1978 P1. As the discoverer, Christy had the right to propose a name. He chose to name the new moon after his wife, Charlene, whose nickname was Shah. Inspired by his interest in physics, where particles like protons and electrons often end in On, he added the suffix to create Karen. It was a personal tribute, but by an almost unbelievable coincidence, it was also a perfect

mythological fit. Only after proposing the name did Christy learn that in Greek mythology, Karen was a silent spectral ferryman who carried the souls of the dead across the river Akaron into the underworld, the realm ruled by the god Pluto. The name was officially adopted by the International Astronomical Union in 1986, but this newfound moon was far more than just a companion. Its very existence would force a complete re-evaluation of the entire solar system, and in doing so, would help topple Pluto from its planetary throne.

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at Indeed.com slash podcast. That's Indeed.com slash podcast. Terms and conditions apply. Need a hiring hero? This is a job for Indeed sponsored jobs. The discovery of Karen immediately began to unravel Pluto's mysteries, and the first revelation was a profound one. By tracking Karen's orbit, astronomers could finally apply Kepler's law to calculate the mass of the system for the first time. The result was shocking. Pluto was not a small terrestrial planet, as some had thought, but was incredibly lightweight, about a sixth of the mass of Earth's moon. Karen itself was found to possess a substantial 12% of Pluto's mass, a ratio far greater than any other major moon in the solar system. Earth's moon, by comparison,

is only about 1.2% of Earth's mass. This startling parity in size gives rise to a unique dynamic that sets the pair apart from every other planet moon system. When a small moon orbits a large planet, the center of their combined mass, or the barry center, lies deep within the planet. The moon makes a large orbit around this point, while the planet makes a tiny wobble. But Pluto and Karen are so close in mass that their barry center lies in the empty space between them, approximately 960 kilometers above Pluto's surface. Pluto and Karen perform a perpetual dance around a common, invisible point in space,

and that has implications. Our moon is tidily locked to Earth. That means it rotates on its axis in the same amount of time it takes to orbit us, which is why it always presents the same face to us. From the moon's surface, however, an astronaut would see. See Earth rotate, going through a full day, night cycle. The Pluto-Karon system is an extreme example of what is called mutual tidal locking. Not only does Keren always show the same face to Pluto, but Pluto always shows the same face to Keren. If you were standing on the Karen-facing side of Pluto, the great moon would hang motionless in the sky, a colossal disc that never rises or sets.

you were on the opposite hemisphere, you would never know it was there at all. They are locked in an eternal stair down across 19,640 kilometers of space. These two facts, the external barricentor and the mutual tidal lock, led many scientists to argue that the system shouldn't be considered a planet and a moon, but rather a double planet. This ambiguity became a central exhibit in the heated debate over planetary definition. definitions in the early 2000s. The discovery of Keran provided the critical data, Pluto's low mass and the system's

strange dynamics, that forced astronomers to confront the fact that the solar system was more complex than our simple categories allowed. The International Astronomical Union even formally considered a proposal to classify Pluto and Karen as a double planet in 2006, though the idea was ultimately set aside amidst the larger, more controversial decision. to reclassify Pluto as a dwarf planet instead. So, I know you're all wondering, how did such a strange system come to be? For many years, the leading theory for the formation of the Pluto-Kerrin system

was a scaled-down version of how our own moon was born, the giant impact hypothesis. In this scenario, a massive Kuiper belt object slammed into a proto-pluto in a cataclysmic collision. The impact would have blasted a huge cloud of debris into orbit, which then gradually coalesced to form Keran. This model successfully explains the system's high angular momentum and Keran's nearly circular orbit. However, as our understanding of planetary materials and our computational power grew, this model started to show cracks.

Pluto and Kerin are not molten bodies of rock like early Earth. They are small, rigid worlds, made of rock and a great deal of water ice. These materials behave very differently under the stress of a cosmic collision. More recent and sophisticated simulations have given rise to a new, more elegant theory. This model proposes a much lower velocity grazing impact, less of a planetary shattering and more of a cosmic kiss. Instead of obliterating each other, the Proto-Pluto and Proto-Keran collided gently enough that they became temporarily stuck together, spinning through space as a single,

snowman-shaped object for a few hours before tidal forces pulled them apart again. They separated, but not completely, remaining forever bound by gravity in the binary system we see today. This kiss-and-capture scenario has a powerful advantage. advantage over the giant impact model, it explains how both bodies could have survived the encounter largely intact, preserving much of their original internal structure and composition. This aligns perfectly with observations that show Pluto is denser and more rock-rich, about 70% rock, than Keran, which is only about 55% rock, suggesting they formed as separate bodies

that were not thoroughly mixed together in a fiery collision. Crucially, this formation story does more than just explain the system's orbit and composition. It provides the key to understanding Kerrins' entire geological history. The initial impact, and, more importantly, the immense tidal friction generated as the two bodies stretched and pulled on each other during their separation, would have deposited a tremendous amount of heat deep inside both worlds. This injected energy is the starter pistol that fired off Keran's geological evolution. Trapped beneath a crust of ice, this heat would melt the interior, creating a subsurface ocean

and setting the stage for the planetary scale drama that would later unfold across its surface. Figuring out Sharon and Pluto's relationship was something of a logic puzzle. The pieces were all there. We just needed to figure out how to decode them. And when we did, it was hugely rewarding. But if logic puzzles like this are up your alley, only you don't have a spare naval observatory to peer up at Karen or Pluto, don't worry. There's something for you right here on Earth with the sponsor of today's video, Brilliant.

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Try it out yourself for free by scanning my QR code or clicking the link Brilliant.org forward slash Astrum in the description below. Astrum viewers get 20% off an annual premium subscription, which gives you unlimited daily access to everything Brilliant has to offer. For 37 years after its discovery, Karen remained little more than a fuzzy companion to Pluto. But on the 14th of July 2015, NASA's New Horizon spacecraft flew past the binary pair, transforming them from distant points of light into vibrant, complex worlds. The images New Horizon sent back from Karen were stunning. They revealed a world that had, at some point in its distant past, torn itself apart. Karen's surface isn't smooth. It's dominated by a system of vast tectonic faults, enormous ridges,

towering cliffs and deep valleys that scar its surface. The most spectacular. The spectacular of these is a great belt of chasms that wraps around the moon's equator. This system, which includes the informally named Serenity Casma, runs for at least 1,800 kilometers and plunges to depths of up to 7.5 kilometers. To put that in perspective, it's more than four times as long and nearly five times as deep as Earth's Grand Canyon. These are not canyons carved by rivers, but colossal pull-apart faults, evidence that the entire crust of Keran was once stretched to its breaking point.

What immense force could cause a whole world to expand and rupture? The answer lies with the heat from its formation. That initial energy, supplemented by the slow decay of radioactive elements in its rocky core, likely enough to melt the water ice deep inside Karen, creating a vast, liquid water ocean beneath a solid frozen crust. For a time, Keran was an ocean world. But all small bodies in the outer solar system eventually lose their primordial heat to space.

As Keran cooled over millions of years, this subsurface ocean began to freeze. Here, a peculiar property of water becomes critically important. Unlike most substances, which contract when they freeze, water expands. As the ocean turned to ice, its volume increased, pushing relentlessly outwards on the brittle, overlying crust from below. The surface stretched and strained until it could hold no longer. The crust of Kerrind ruptured, creating vast canyon systems that still still, span the dwarf planet today.

As one scientist put it, Karen tore itself apart at the seams like Bruce Banner becoming the Hulk. Today, Karen appears to be geologically inert. Its period of great upheaval is long past. Because it lacks a thick atmosphere or ongoing geological activity to erode or bury these features, the evidence of this ancient cataclysm is well preserved. The surface of Keran is not just a landscape, it's a frozen snapshot of the death of its ocean. The freezing of Keran's ocean did more than just break its crust.

It also paved over half the world. The New Horizons images revealed a tale of two hemispheres with dramatically different stories. The northern hemisphere, informally named Oz Terra, is an ancient battered world with rugged, high-standing terrain, heavily created and crisscrossed by the vast network of tectonic faults and canyons created by the expanding interior. This is the original crust of Kerin, frozen in its fractured state. But to the south, the landscape transforms. This is Vulcan Planitia, a vast, smooth plain that's starkly different from the torture

lands of the north. This region is far less created, indicating. that it is a much younger surface. It sits at a lower elevation than Oz Terra, and its surface is marked by features that look like frozen flows and broad swells. Scientists believe Vulcan Plenicia is one of the most extensive examples of cryovulcanism in the solar system. These weren't volcanoes of molten rock, but icy slush. As the subsurface ocean froze, the expansion not only cracked crust, but also pressurized the liquid water below, which was likely mixed with ammonia that acted as a sort of antifreeze. This pressurized cryomagma was forced upward through the newly

formed cracks and fissures erupting onto the surface. Icey lava flooded the southern hemisphere, creating the smooth, young plains of Vulcan Plannum. Scattered across these plains are several large isolated mountains such as Kubrickmonds, which appear to sit in strange depressions or moats. These may be colossal blocks of the older northern crust that broke off, were carried along like icebergs on the cry of volcanic flows and left stranded as the planes froze solid around them. Perhaps the most visually arresting and mysterious feature on Karen is its North Pole. Capping the top of the moon is a large, dark, reddish-brown stain,

a feature so prominent that the New Horizons team informally named it Mordor Macula, after the black land from the Lord of the Rings. The colour is almost certainly caused by a class of complex organic molecules called tholins. Tholins are a reddish, tar-like substance formed with, when simple organic compounds, particularly methane, are irradiated by the sun's ultraviolet light and cosmic rays. Tholins are common in the outer solar system, but their concentration at Kerrins' pole is unique. The key to understanding why they are here is to find the source of the methane.

There are two competing theories. The leading hypothesis is that the methane is a gift from Pluto and its atmosphere rich in nitrogen and methane that's slowly escaping into space. As Karen orbits, its gravity captures some of this lost gas. During Karen's long, dark polar winter, which lasts for more than a century, temperatures plummet to below minus 240 degrees Celsius. At these extreme temperatures, the capture methane freezes directly onto the surface in a process known as cold trapping.

the pole finally swings back into sunlight, the accumulated methane ice is bombarded with UV radiation, which cooks it into the reddish tholins that stay in the pole. Karen and Pluto are then a dynamic, interconnected system, with one world actively painting the surface of its companion across thousands of kilometers of space. But a competing theory suggests that methane was an inside job, that it originated from Keran's own interior. The massive cryovulcanic eruptions that formed Vulcan Plenicia would have also released enormous quantities of gas, including methane that were dissolved in the subsurface ocean.

This would have created a temporary atmosphere on Keran, and just as in the first hypothesis, methane would have migrated to the coldest parts of the moon, the poles, and frozen out. For billions of years, this native methane deposit was then irradiated to form Mordor Macula. This theory elegantly ties the origin of the polar cap directly to the other major geological events that shape the moon. Whether the methane came from Pluto's atmosphere or Keran's own interior, Mordor macula is a visible testament to the inescapable connection between these two distant worlds, a direct product of their shared history and environment.

Our journey began with a smudge on a photographic plate that was nearly dismissed as an error. It ends with a complex and dramatic world, a world of continent spanning canyons deeper than any on Earth, vast plains of ancient ice lava, and a mysterious red-stained pole. It's impossible to tell the story of Pluto without Keren. It was Keren's orbit.

that gave us the first true measure of Pluto's mass, revealing it as the king of a new class of worlds. It was Keran's existence that pointed to a shared, violent birth that sculpted both bodies and ejected them with the heat that would fuel their evolution. It's Keran's fractured surface that tells a story of a lost ocean, a geological history that provides a crucial context for understanding the forces that may still be churning deep inside the more active Pluto today, and it's Keran's red pole that may serve as a permanent record of Pluto's atmosphere, bleeding out into space over the eons. In mythology, Keran the ferryman was an inseparable and essential figure in Pluto's

realm. Science has revealed this to be profoundly true. Keran is not a moon orbiting a dwarf planet, it is the other half of a unique binary system forever locked in a silent, eternal dance with Pluto. Its story is a powerful reminder that our greatest discoveries can hide in our mistakes, and that even the most distant, frozen, and seemingly quiet corners of our solar system hold histories more fiery and dramatic than we could ever imagine. Thanks for watching. I'd like to take a moment to thank a special supernovae

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