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 m Kaj
Strand telescope in Arizona were not
considered highquality. 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
Christy 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 the
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 too 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 systematically 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 S1978
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 Sha.
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 fairyman who carried the
souls of the dead across the river Aaron
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 [music] its
planetary throne.
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 km 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 Earth rotate going through a
full day night cycle. The Pluto Karen
system is an extreme example of what is
called mutual tidal locking. Not only
does Karen always show the same face to
Pluto, but Pluto always shows the same
face to Karen. 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. If you were on the opposite
hemisphere, you would never know it was
there at all. They are locked in an
eternal staredown across 19,640
km of space. These two facts, the
external barry center 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 definitions in the early
2000s. The discovery of Karin provided
the critical data, Pluto's low mass and
the systems 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 Karin system was
a scaledown version of how our own moon
was born, the giant impact hypothesis.
In this scenario, a massive Kyper 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 coalesed
[music] to form Karin. This model
successfully explains the systems high
angular momentum and Karen's nearly
circular orbit. However, as our
understanding of planetary materials and
[music] our computational power grew,
this model started to show cracks. Pluto
and Karen are not molten bodies of rock
like early Earth. They are small, rigid
worlds made of rock and [music] 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, [music] more elegant
theory. This model proposes a much lower
velocity [music]
grazing impact, less of a planetary
shattering and more of a cosmic kiss.
Instead of obliterating each other, the
Proto Pluto and Protoarin 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 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,
about 70% rock, than Karen, which is
only about 55% rock, suggesting they
formed as separate [music] bodies that
were not thoroughly mixed together in a
fiery collision. Crucially, this
formation story does more than just
explain the systems [music] orbit and
composition. It provides the key to
understanding Karen's entire geological
history. The initial impact and [music]
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 Karen'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. [music]
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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 of these
is a great belt of chasms that wraps
around the moon's equator. This system,
which includes the informally named
Serenity Chasma, runs for at least 1,800
km and plunges to depths of up to 7.5
km. To put that in perspective, it's
[music] 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 aart faults, evidence
that the entire crust of Karan 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 was likely enough to melt the
water ice deep inside Karen, creating a
vast liquid water ocean beneath a solid
frozen crust. For a time, Karen was an
ocean world. But all small bodies in the
outer solar system eventually lose their
primordial heat to space. As Karan
cooled over millions of years, this
subsurface ocean began [music] to
freeze. Here a peculiar property of
water becomes critically important.
Unlike most substances [music]
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 [music] and
strained until it could hold no longer.
The crust of Karan ruptured, creating
vast canyon systems that still span the
dwarf planet today. As one scientist put
it, Karan 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 Kerin is not just a landscape. It's a
frozen snapshot of the death of its
ocean.
The freezing of Karen's ocean did more
than just break its crust. It also paved
over half the world. The New Horizon's
images revealed a tale of two
hemispheres with dramatically different
stories. The northern hemisphere,
informally named Oz Terror, is an
ancient battered world with rugged,
high-standing terrain, heavily created
and crisscrossed by the vast network of
tectonic faults and canyons [music]
created by the expanding interior. This
is the original crust of Karin, frozen
in its fractured state. But to the
south, the landscape transforms. This is
Vulcan Planenicia, a vast smooth plane
that's starkly different from the
torture lands of the north. This region
is far less cratered, indicating that it
is a much younger surface. It sits at a
lower elevation than Oz Terror, and its
surface is marked by features that look
like frozen flows and broad swells.
Scientists believe Vulcan Penicia is one
of the most extensive examples of cryo
volcanism in the solar system. These
weren't volcanoes of molten rock,
[music] but icy slush.
As the subsurface ocean froze, the
expansion not only cracked the crust,
but also pressurized the liquid water
below, which was likely mixed with
ammonia that acted as a sort of
antifreeze. [music]
This pressurized cryomagma was forced
upward through the newly formed [music]
cracks and fishes erupting onto the
surface.
Icy lava flooded the southern hemisphere
creating the smooth young plains of
Vulcan Plenum.
Scattered across these plains are
several large isolated mountains such as
Kubrimons which appear to sit in strange
depressions or moes. These may be
colossal blocks of the older northern
crust that broke off, were carried along
like icebergs on the cryovcanic 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
Horizon's team informally named it
Mordor macula after the black land from
the Lord of the Rings. The color is
almost certainly caused by a class of
complex organic molecules called
tholins. Tholins are a reddish tarlike
substance formed when simple organic
compounds, particularly methane, are
radiated by the sun's ultraviolet light
and cosmic rays. Tholians are common in
the outer solar system, but their
concentration at Karen's 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°
C. At these extreme temperatures, the
captured methane freezes directly onto
the surface in a process known as cold
trapping. When the pole finally swings
back into sunlight, the accumulated
methane ice is bombarded with UV
radiation, which cooks it into the
reddish tholins that stain 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 the
methane was an inside job, that it
originated from Karin's own interior.
The massive cryovcanic 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 Karen.
And just as in the first hypothesis,
methane would have migrated to the
coldest parts of the moon, the poles,
and frozen out over 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 Karen's own interior,
Mordormacula 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
continents 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 Karen. It was Karen'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 Karen'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
Karen's fractured surface that [music]
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 [music] Karen's red pole that may
serve as a permanent record of Pluto's
atmosphere bleeding [music] out into
space over the eons. In mythology, Karen
the Fairyman was an inseparable and
essential figure in Pluto's realm.
Science has revealed this to be
profoundly true. Karen 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 [music] could ever imagine.