For more than 70 years, we thought our
map of the solar system was complete. A
familiar and tidy collection of nine
worlds orbiting a single star. But far
out in the frozen darkness, billions of
kilometers from the furthest known
planet, a ghost was lurking. A tiny
point of light slowly, almost
imperceptibly
drifting across astronomers forgotten
photographs, unnoticed and unknown for
years.
Its discovery wouldn't just add a tenth
name to the roster of planets orbiting
our sun. It would trigger an identity
crisis for the solar system itself,
forcing astronomers into a bitter
conflict over the meaning of one of the
most fundamental words and in the
process redrawing our map of the solar
system forever. This is the story of the
world that true to its name sowed
discord in the scientific community.
I'm Alex Mccoan and you're watching
Astramm. Join me today as we travel to
the chaotic outer edges of our solar
system to meet Eerys, the world that
started a war over the meaning of a
single word, planet.
The story of Aris begins not with a
lucky glance through a telescope, but
with a monumental effort to take an
inventory of the sun's most distant
subjects.
At the Palomar Observatory in
California, a team of astronomers Mike
Brown, Chad Truo, and David Rabinovitz
had embarked on a systematic survey of
the outer reaches of our solar system,
looking for signs of objects orbiting
beyond Neptune, dubbed Trans Neptunian
objects or TNOs.
The team were using the 1.2 2 m Samuel
Oshin telescope to capture images of a
wide field of the sky, putting them
through automated image searching
software that flagged objects moving at
a certain speed. And their search had
already proved fruitful with newly
discovered worlds like Kuawa, Orcus, and
Sednner. They were gradually populating
this dark, distant realm. But the team
were hoping to find something bigger. As
Mike Brown later wrote, "There had to be
a tenth planet. The possibility that
Pluto was a unique planetary oddball out
at the edge of the solar system seemed
absurd to me." He decided to manually
re-examine some old data sets that his
software had passed over. Then, after
months of rechecking, on the 5th of
January 2005, Brown began clicking
through a sequence of three images from
the 21st of October 2003. And there in
the images was a single faint dot of
light moving at a glacial pace against
the background of fixed stars. Brown
knew instantly that this was something
significant. It was bright, meaning it
was either large or highly reflective,
and it was moving far slower than
anything they had found before, meaning
it was incredibly far away. His first
thought was, "I found a planet."
The team began tracking the object
provisionally designated 2003 UB313
to determine its orbit and size. They
had planned to keep their discovery
under wraps until they had completed
further observations, but the
competitive world of planetary science
intervened. On the 27th of July 2005, a
different team controversially announced
the discovery of another large TNO home
after accessing Brown's team's public
observation logs. To avoid being scooped
again, Brown's team was forced to go
public. On the 29th of July, they
announced the discovery of not just one,
but two major bodies in the outer solar
system. Howa and this new object that
would eventually become known as Aerys.
The secret was out and the solar system
would never be the same.
In Greek mythology, Aris is the goddess
of strife, a malevolent deity who when
snubbed from a wedding tossed a golden
apple inscribed for the fairest among
the goddesses, instigating a quarrel
that led directly to the Trojan War. In
2005, the discovery of the celestial
body that would bear her name was the
modern equivalent of that golden apple.
Thrown into the halls of astronomy. It
ignited a scientific war over the very
definition of a planet. The problem was
simple yet profound. Initial estimates
suggested AIS was larger than Pluto, and
subsequent calculations based on its
moon's orbit showed it was 27% more
massive. If Pluto was a planet, then
Aerys, its more massive twin, certainly
had to be one as well. And if Aerys was
a planet, what about the other large
TNOs that had recently been discovered,
such as Maka,
and Sedna? Where would the line be
drawn? The discovery created an
unavoidable logical crisis. As Mike
Brown put it, we were either going to
have to add new planets or subtract one.
The International Astronomical Union,
the global body responsible for
astronomical nomenclature, was forced to
act. At its 26th General Assembly in
Prague in August 2006, the question of
what is a planet was put to a formal
debate and vote for the first time in
history. The debate was vigorous and
exposed a deep rift within the
astronomical community, splitting it
into two main camps. On one side were
those who advocated for a geoysical
definition. They argued that a planet
should be defined by its intrinsic
properties. If an object is massive
enough for its own gravity to overcome
its material strength and pull it into a
nearly round shape, a state known as
hydrostatic equilibrium, it should be
called a planet.
Under this simple definition, Pluto,
Ays, the dwarf planet series, and
potentially dozens of other bodies would
have become planets.
On the other side were those who favored
a dynamical definition. They argued that
a planet's identity is tied not just to
its physical state, but to its
gravitational influence on its
surroundings. A true planet, they
contended, must be the dominant
gravitational player in its orbital
zone. In the words of the final
resolution, it must have cleared the
neighborhood around its orbit. The
voting process itself was fraught with
controversy. The final vote was held on
the last day of the 10-day conference,
by which time most of the 2,500
attendees had already gone home. Only
424 astronomers were present to cast
their ballots, a tiny fraction of the
global astronomical community. When the
votes were counted, the dynamical
definition had won. The IAU passed
resolution 5A establishing a threepart
definition for a planet in the solar
system. It must a be in orbit around the
sun, b be in hydrostatic equilibrium and
c have cleared its neighborhood.
Pluto sharing its orbital space with
Neptune and a host of other Kyber belt
objects failed on the third criterion.
A new category was created, the dwarf
planet for objects that meet the first
two criteria but not the third.
Crucially, a follow-up resolution was
defeated that would have made dwarf
planets a subcategory of planet.
Instead, the IAU declared that planets
and dwarf planets are two distinct
classes of objects. In an instant, the
solar system was officially reduced to
just eight planets. Critics immediately
pointed out flaws in this definition.
The phrase clear the neighborhood was
ambiguous and the first criterion in
orbit around the sun applied only to our
solar system and ignored the thousands
of exoplanets that we now know exist. It
was not a universal, elegant principle,
but a reactive, controversial, and local
fix. With the debate settled, at least
officially, the Discovery team had the
honor of naming their troublemaking
world. They chose EIS, a name Mike Brown
felt was perfect for the object that had
thrown astronomy into such strife. The
name was formally accepted in September
2006, cementing the legacy of this
distant world as the celestial apple of
discord.
If Pluto could think, it would no doubt
have found itself disappointed at no
longer being a planet anymore. But with
the change came many winners. For
instance, series, formerly considered an
asteroid, was able to take its place
among the new rank of dwarf planets in
2006. Are you looking for a similar
giving you unlimited access to all Brilliant has to offer.
Having established its role as a cosmic
disruptor, it's time to journey to Aerys
itself and understand the nature of this
renegade world. Eris does not reside in
the relatively stable disc-like Kyper
belt, the home of Pluto and many other
icy bodies. Instead, it belongs to a far
more chaotic and wild region known as
the Scattered Dis. The Scattered Disc is
a vast, sparssely populated halo of icy
objects with extreme orbits. These are
the solar systems outcasts. Bodies that
likely formed closer to the sun, but
were gravitationally scattered into
their current paths by Neptune as it
migrated into its current orbit billions
of years ago. Aris's orbit isn't a
circle like you might expect, but a huge
ellipse that takes it 557
Earth years to trace. At its closest
approach or perihelion, Aerys comes
within about 38 astronomical units of
the sun, roughly the same distance as
Pluto's average orbit. But at its
furthest point, or appelion, it swings
out nearly 98 astronomical units, almost
15 billion km away. That's nearly three
times Pluto's current distance from the
sun. Aris's orbit is also steeply
inclined at 44° to the ecliptic, the
plane on which the main planets travel.
This means Aerys spends its 557 Earthy
year-earlong year soaring high above and
plunging far below the rest of the solar
system.
For years, Aerys was thought to be
Pluto's larger twin. But in 2010,
astronomers had a chance to measure it
with incredible precision. Ays passed
directly in front of a distant star, an
event known as a stellar occultation. By
timing how long the stars light was
blocked from different locations on
Earth, they could calculate its size
with pinpoint accuracy. The result was a
surprise. With a diameter of 2,326
km, Eris was almost exactly the same
size as Pluto and in fact slightly
smaller. This revealed the most crucial
difference between the two worlds. With
a mass 27% greater than Pluto's packed
into a slightly smaller volume, AIS must
be significantly denser. Scientists
calculated its density at 2.43 g per cm,
substantially higher than Pluto's 1.85 g
per cm. This points to a very different
internal structure. While Pluto is
thought to be a roughly 7030% mix of
rock and ice, Eris must be composed
predominantly of rock with only a
comparatively thin mantle of ice on top,
a rocky heart in a frozen shell. That
shell is also one of the most brilliant
surfaces in the solar system. Aris has
an incredibly high albido of 0.99,
meaning it reflects 99% of the sunlight
that reaches it. This dazzling
brightness is potentially due to a
phenomenon called atmospheric collapse.
Like Pluto, Aerys has an atmosphere
primarily composed of nitrogen and
methane ice that is turned to gas. But
as its extreme orbit carries it into the
deep freeze of its apphelion, this
atmosphere freezes solid and falls to
the surface as a fresh bright layer of
frost or snow. As Aris begins its
280year journey back towards the sun,
this frost will warm and sublimate,
turning back into a gas and renewing the
atmosphere, only to freeze and fall
again centuries later.
And more recently, observations from the
James Webb Space Telescope have added
another layer of complexity. Analysis of
different isotopes of methane on Eris's
surface suggests they may have been
produced by geothermal activity, hinting
at unexpected thermal processes deep
within its rocky core. This distant
frozen world may have, or at least once
had a warm heart.
The key to unlocking Eris's secrets and
the final piece of evidence that would
seal Pluto's fate came in September 2005
using the advanced adaptive optic system
on the WM KEK telescope, a telescope
that corrects for the blurring effects
of Earth's atmosphere to produce space
telescope quality images. Mike Brown and
his team spotted a faint companion
orbiting Aerys. It had a moon. This
changed everything. While an object's
size can be estimated from its
brightness, its mass can only be
determined with certainty by observing
its gravitational pull on another body,
for instance, a natural satellite. By
carefully tracking the moon's nearly
circular 16-day orbit, the team could
apply Kepler's law of planetary motion
to calculate the mass of AIS with great
precision. It was this calculation that
definitively proved Aris was more
massive than Pluto, making the planet
debate not just an academic exercise,
but an urgent necessity. The moon itself
is a stark contrast to its parent. While
only 25% the diameter of Ays, this moon
is one of the largest of any dwarf
planet, second only to Pluto's own
Kerin, and larger than Saturn's
Enceladus or Mimis. It's also tidily
locked to Aerys, but estimates of its
mass from how much it causes Aerys to
wobble in its position are far below
what would usually allow tidal locking.
This suggests that Aerys itself
dissipates energy far more easily than
we first thought. While Aerys is
brilliant white, its moon is incredibly
dark. Described as being darker than
coal, this suggests a very different
surface composition, devoid of the
bright frosts that coat Ays, the leading
hypothesis for the moon's origin is a
giant impact, much like the one that
formed Earth's moon. Early in the solar
systems history, a massive object likely
slammed into the young Aerys, blasting a
cloud of debris into orbit that
eventually coalesed to form a single
satellite. This violent birth would have
stripped away volatile ices, leaving
behind a darker, rockier body. Just as
Aris was named for the goddess of
discord, her moon was given the name of
her mythological daughter, this Nomia,
the demon spirit of lawlessness.
The name is fitting for a moon born from
chaos, orbiting a world that overturned
the established laws of the solar
system.
In the years since the 2006 vote, Mike
Brown has earned the name the Pluto
Killer. But this misses the true legacy
of his discovery. Finding Aerys didn't
kill Pluto. It revealed Pluto's true
family, making our solar system larger,
more complex, and more interesting. For
decades, we had a flawed model. Eight
planets of a certain character, and then
one strange outlier. By forcing this
reclassification, Aris gave us a more
accurate and coherent picture of our
cosmic home. There are four inner rocky
terrestrial planets. There are four gas
and ice giants. And beyond them lies a
vast third realm, a swarm of thousands
of icy dwarf planets, a population of
worlds whose existence we were only just
beginning to grasp. Eris and Pluto are
kings of this third zone, the largest
and most prominent members of the Trans
Neptunian population discovered so far.
And Aerys itself remains the ultimate
mystery. It is the most massive known
object in our solar system that has not
been yet visited by a spacecraft. While
NASA's New Horizon's mission gave us a
breathtaking intimate portrait of Pluto,
Aerys remains a distant point of light.
its secrets held across billions of
kilometers of empty space. A proposed
flyby mission would take an estimated 25
years just to reach its destination, a
journey that would span generations.
For the foreseeable future, the goddess
of discord will keep her secrets.
Her discovery resolved one great debate,
but it opened up a new chapter in our
exploration of the solar system,
reminding us that the most exciting
discoveries are not those that provide
the final answers, but those that reveal
just how much more there is left to
explore.
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