In August of 2006, a group of astronomers gathered
in Prague to make a decision. A vote was taken,
and with that vote, a planet died. Pluto, the
ninth planet many of us grew up memorizing in
school, was suddenly gone. Demoted, reclassified,
and stripped of its planetary status. The story
of Pluto has always been complex. This was a
world predicted before it was seen, discovered
by a farm boy who loved astronomy and named by
an 11 -year -old girl. And decades after its
supposed downfall, a spacecraft arrived to reveal
something extraordinary. Tonight, we reopen the
case. My name is Drew, and this is Star Trails.
Howdy stargazers and welcome to this episode
of Star Trails for the week of March the 15th
through the 21st. This week we look at the discovery
and life of our former ninth planet, Pluto. Its
murder nearly two decades ago, and its rebirth
as one of the most intriguing outposts of our
solar system. Later in the show, we'll see what's
happening in this week's sky. Whether you're
tuning in from the backyard or the balcony, I'm
glad you're here. So grab a comfortable spot
under the night sky and let's get started. Tonight
we're opening a case file. Not a criminal case,
but a cosmic one. And this story has all the
elements of a good mystery. There are predictions,
a long search, a young discoverer, a controversial
trial, and years later, an unexpected redemption.
So tonight, we're going to investigate what might
be the strangest planetary story ever told, the
case of Pluto. Our story begins in the late 1800s.
Astronomers studying the orbit of Uranus noticed
something strange. The planet wasn't exactly
where it should have been. Its motion suggested
that something unseen, something massive, was
tugging on it from farther out in the solar system.
This had happened once before. In fact, the planet
Neptune had been discovered precisely this way,
predicted mathematically before anyone ever saw
it through a telescope. So naturally, astronomers
wondered, was there another planet out there?
One more world lurking in the darkness beyond
Neptune. This hypothetical object became known
as Planet X, and one man became obsessed with
finding it. His name was Percival Lowell. Lowell
was a wealthy astronomer who founded the Lowell
Observatory in Flagstaff, Arizona. Today, the
observatory is famous for one particular discovery,
but in Lowell's time it was built largely for
a single purpose, to find Planet X. Lowell calculated
where this mysterious world might be hiding and
began photographing regions of the sky, searching
for something that moved against the background
stars. But the task was enormous because the
sky is vast. and the planet, if it existed, would
be incredibly faint. Lowell never found it. He
died in 1916. And for a while, the case went
cold. More than a decade later, the investigation
resumed, and the man who picked up the search
was not a famous scientist. He was a farm kid
from Kansas named Clyde Tombow. Tom Bow had grown
up building telescopes out of spare tractor parts
and studying the night sky from his family's
farm. He eventually sent detailed drawings of
Mars and Jupiter to Lowell Observatory. The staff
were impressed, so they offered him a job. His
task was simple. Photograph the sky and look
for something moving. To do this, Tom Bow used
a machine called a Blink Comparator. If you've
ever flipped between two nearly identical photos
looking for the difference, you already understand
the idea. Two photographic plates of the same
patch of sky are placed into the machine. Then
the device rapidly switches your view back and
forth between them. The stars remain fixed, but
anything moving, like a comet, asteroid, or a
planet, jumps back and forth. For months, Tom
Bow stared into that machine, scanning thousands
upon thousands of stars. Then, on February 18,
1930, he saw it. A tiny speck of light, not much
larger than a speck of dust, moving between two
photographs taken weeks apart. Tom Bow, just
24 years old, had discovered a new world. See,
when I took the photographs, I had no idea. that
put his image on those plates. This is Clyde
Tombaugh in an interview recorded in 1991. Factors
several weeks later, when I got to that pair,
and I encountered as I'm going through all these
alternating views of star fields, and here's
one that shifted position by the right amount.
Now I had figured out beforehand that if there
was a Planet X, how would I recognize it if I
encountered it, you see? So I thought all this
out beforehand. And so when it came there, it
was instantly I realized I had found a planet
beyond the orbit of Neptune by the amount of
shift. I knew the scale of the plates. I knew
the interval. It's just a matter of geometry.
That was the most instantaneous sail you could
imagine. It just electrified me. And that was
the 18th of February, 1930. The discovery electrified
the world too. Newspapers called it the ninth
planet, and suddenly everyone wanted to name
it. Thousands of suggestions poured in from around
the globe, but the winning idea came from an
11 -year -old girl in Oxford named Venetia Burney.
Her suggestion? Pluto, the Roman god of the underworld.
It was a perfect name. Pluto ruled a dark, distant
realm far from the sun. and the first two letters,
P and L, also honored Percival Lowell, whose
search had started the whole investigation. Later
that same year, Walt Disney introduced a new
character, Mickey Mouse's dog. His name was Pluto,
and he was almost certainly named after the newly
discovered planet that had captured the world's
imagination. Not bad for a frozen world billions
of miles away. For decades, Pluto remained mysterious.
First, it's incredibly distant. Its orbit takes
it from about 2 .7 to 4 .6 billion miles from
the Sun. One trip around the Sun takes 248 Earth
years, which means Pluto has not even completed
a full orbit since the day it was discovered.
Its orbit is also tilted and elongated. unlike
the nearly circular paths of the major planets.
Sometimes Pluto actually comes closer to the
Sun than Neptune. That happened from 1979 to
1999. Despite that overlap, the two worlds never
collide because Pluto is locked in a three -to
-two orbital resonance with Neptune. Pluto is
also tiny. It's just 2 ,377 kilometers across.
making it smaller than Earth's moon. Its surface
is made of exotic ices, nitrogen, methane, and
water ice, existing at temperatures around minus
375 degrees Fahrenheit or colder. For much of
the 20th century, astronomers assumed Pluto was
probably a cold, inactive world. a lonely outpost
at the edge of the solar system. But then another
discovery complicated the story. In 1978, astronomer
James Christie noticed something strange while
studying telescope images of Pluto. The planet
appeared slightly elongated, almost as if there
were a bump sticking out of one side. At first,
he assumed it was an error in the image, but
the bump kept appearing. and its position kept
changing. Christie realized what he was seeing.
Pluto had a moon. The moon was named Charon after
the fairy man of the dead in Greek mythology
who carried souls across the river Styx to Pluto's
realm. Charon turned out to be enormous relative
to Pluto, about half of Pluto's diameter. So
large, in fact, that the two worlds orbit a point
in space between them rather than Charon simply
circling Pluto. In some ways, Pluto and Charon
are better described as a binary planetary system,
and later observations revealed even more companions.
Four smaller moons named Nix, Hydra, Kerberos,
and Styx. But by this point, astronomers were
beginning to notice something else, something
that would eventually lead to Pluto's downfall.
Beginning in the 1990s, astronomers discovered
hundreds of icy bodies beyond Neptune. This region
became known as the Kuiper Belt, and suddenly
Pluto didn't look so unique anymore. It looked
like one member of a much larger population of
distant icy worlds. Then in 2005, astronomers
discovered an object called Eris, roughly comparable
in size to Pluto. And that forced a very uncomfortable
question. If Pluto is a planet, should Eris be
a planet too? And if Eris is a planet, how many
more planets might we find out there? Dozens,
hundreds, maybe more. In 2006, the International
Astronomical Union convened a meeting in Prague
to settle the issue. Astronomers debated a deceptively
simple question. What is a planet? After deliberation,
a new definition was adopted. To qualify as a
planet, a body must orbit the sun, it must be
round due to its own gravity, and it must clear
its orbital neighborhood of other objects. Pluto
failed that last requirement. It shares its region
of space with many Kuiper Belt objects. And so
the verdict came down. Pluto was no longer part
of the starting lineup. It was reclassified as
a dwarf planet. And many astronomers supported
the decision. Among the most visible voices explaining
the change to the public was astrophysicist Neil
deGrasse Tyson. who had already removed Pluto
from the planetary lineup at the Hayden Planetarium
years earlier. But the astronomer who calls himself
the real Pluto killer is Mike Brown of Caltech.
Brown had spent years surveying the outer solar
system and was convinced that Pluto was not a
unique planet but simply a member of a much bigger
population of icy bodies beyond Neptune. As his
team began discovering more and more large Kuiper
Belt objects, Brown openly argued that astronomers
would eventually have to face a choice. Either
accept dozens of new planets, or rethink Pluto's
status entirely. After 76 years of glory, Pluto
was demoted from being considered one of nine
planets in our solar system to just a dwarf planet.
And the scientists who made the discovery will
always be known as the man who killed Pluto.
Pluto's not a planet because it's part of this
vast swarm of bodies out beyond Neptune in what
we now call the Kuiper belt. There are thousands,
millions of objects out there of which Pluto
is only the second most massive. Mike Brown,
a professor at Caltech, says he We will never
hear the end of it. Mostly it was adults thinking
of their childhood memory that were upset. Brown's
discoveries were what truly pushed the debate
to its breaking point. But for many Pluto fans,
Tyson became the public face of the decision.
Here he is chatting with Stephen Colbert about
being an accessory to the ruling. discovered
the objects in the outer solar system that forced
that vote. In fact, he's guilty. In fact, his
Twitter handle is called Pluto Killer. He admits
it. Who is this Mike Brown you're throwing under
the bus right now? Under the space bus. He put
himself under the bus. I'm pointing it out. But
here's the thing is that now some of your buddies
at NASA want to reinstate Pluto as a planet because
they want the designation of planet to be closer
to people's intuition rather than some arbitrary
scientific designation. Okay. They should just
like get over it. OK. Why do you think people
want to name it a planet? Pluto had it coming
from the beginning. It was never really belong.
Pluto's orbit crosses that of another planet.
That's no kind of behavior for a planet. No!
You got to stay in your lane. Stay in your lane!
Stay in your lane! All right, OK. No! Clyde Tombaugh
passed away in 1997, but his connection to Pluto
didn't end there. When NASA launched the spacecraft
New Horizons in 2006, the very same year Pluto
was demoted, a small portion of Tom Bow's ashes
was placed aboard the spacecraft. Nine years
later, that spacecraft arrived at Pluto, symbolically
carrying its discoverer to the world he had found.
Few scientists in history have ever traveled,
at least in spirit, to visit their own discovery.
When New Horizons flew past Pluto on July the
14th 2015, the images it sent back stunned the
world. Pluto was not a frozen relic. It had towering
mountains made of water ice, vast glaciers of
frozen nitrogen, a thin blue atmosphere, and
a giant heart -shaped plane. Pluto even has a
strange seasonal atmosphere made mostly of nitrogen.
As the dwarf planet moves farther from the Sun,
that atmosphere can actually freeze and fall
back to the surface like frost. Some scientists
even think Pluto may hide a subsurface ocean
beneath its icy crust. Against all expectations,
Pluto appeared geologically active, dynamic,
and alive with strange processes scientists are
still trying to understand. For a world barely
half the size of Earth's moon, it turned out
to be astonishingly complex. And for some, that
meant Pluto is a planet. You could really undercut
all the planets. They're all dwarf planets because
there isn't a planet that clears its entire orbit
around the sun. That's former NASA Administrator
Jim Bridenstine. I think the way you should define
a planet... is based on its intrinsic values,
not the values that constantly change like orbital
dynamics. So when I think about Pluto and what
we got back from New Horizons, here's what we
know. Pluto has an ocean under its surface. Pluto
has complex organic compounds on its surface.
Pluto has a multi -layer atmosphere and Pluto
has its own moons. I'm here to tell you, as the
NASA administrator, I believe Pluto is a planet.
Today, the verdict of 2006 still stands. Pluto
remains officially classified as a dwarf planet.
Every February, hundreds of people travel to
northern Arizona to celebrate Pluto at the place
where it was discovered, the historic Lowell
Observatory. The event is called the I Heart
Pluto Festival, and it's part science conference,
part community celebration, and part love letter
to the distant world. Visitors attend astronomy
lectures, telescope demonstrations, and talks
from planetary scientists. There are art exhibits,
science presentations, and even a pub crawl through
downtown Flagstaff, where astronomers give short
talks about Pluto between stops. the man who
discovered Pluto. Well the events that Lowell
Observatory and Flagstaff have put on are always
very important to us. We very much appreciate
the honors that they have been given to my father
and to his accomplishments here at Lowell Observatory
and in Flagstaff. It may sound like an unusual
festival but it speaks to something deeper. Pluto's
discovery in 1930 was one of the great moments
in American astronomy. and the city of Flagstaff
still takes pride in being the place where a
faint speck of light first revealed a new world.
Pluto was the only planet discovered in the United
States, and Americans love an underdog. Pluto
being the smallest planet certainly fits the
bill. If there's one lesson here, it's this.
Pluto was never the end of the solar system.
It's the first visible member of an entire neighborhood
we hadn't discovered yet. That neighborhood is
the Kuiper Belt, a vast disk of icy leftovers
from the era when the planets were forming about
four and a half billion years ago. The Belt begins
just beyond Neptune, roughly 30 astronomical
units from the Sun, and extends outward at least
a 50 AU and maybe further. Pluto is the first
house on the street leading out into the suburbs
of our solar system. The front porch of the Kuiper
Belt, perhaps. The real mystery is how many more
worlds are still waiting to be found. And that
makes Pluto less like a fallen planet, and more
like the cosmic welcome sign to an undiscovered
country. After a quick break, I'll tell you what
you can expect to see in this week's night sky.
Stay with us. Welcome back. Now that we've closed
the case file on Pluto, let's turn our attention
to the sky above us this week. Mid -March is
a beautiful time for backyard astronomers. Winter's
constellations are slowly slipping westward.
The first hints of spring are rising in the east,
and the night sky itself feels like it's in the
middle of a seasonal handoff. So if you're stepping
outside this week, here's what you can expect
to find. We'll begin with the moon. It's moving
through its waning crescent phase during most
of this week. You'll see it rising in the early
morning hours, appearing as a delicate, curved
sliver before sunrise. The new moon arrives at
week's end, leading to inky dark skies suitable
for deep sky observation. And March the 20th
brings another milestone. That's the vernal equinox,
the official beginning of spring in the Northern
Hemisphere. On this day, the Sun crosses the
celestial equator and day and night become nearly
equal in length. Astronomically speaking, it
also means the night sky is beginning its seasonal
transformation. Winter constellations like Orion
and Taurus are drifting westward, while the stars
of spring begin climbing into the eastern sky.
If you live somewhere with reasonably dark skies,
this week offers a wonderful opportunity to spot
something many observers have never seen before,
the zodiacal light. About 20 minutes after sunset,
look toward the western horizon. Under dark conditions,
you may notice a faint triangular glow rising
upward along the path of the planets. This ghostly
pillar of light is sunlight reflecting off millions
of tiny dust particles that fill the inner solar
system, leftovers from comet tails and asteroid
collisions. March is one of the best times of
year to see it because the angle of the solar
system's plane is steep against the evening horizon
near the spring equinox. If you've never seen
it before, it looks almost like a faint, tilted
beam of twilight reaching up into the stars.
This week also offers several planets to explore.
First up is Jupiter, which remains one of the
brightest objects in the night sky this month.
It shines prominently in the constellation Gemini,
easily visible in the evening and remaining high
in the sky for much of the night. If you step
outside after sunset, Jupiter will likely be
the first planet your eye catches. Its brightness
is startling. Low in the western sky, you may
still catch Venus in the evening twilight, though
it sets fairly quickly. Saturn has been slipping
towards the Sun's glare and is becoming difficult
to observe now, lingering very low near the horizon
shortly after sunset. With binoculars or a telescope,
you can also try tracking down Uranus, which
sits in the constellation Taurus, not far from
the famous Pleiades star cluster. Through binoculars,
Uranus appears as a tiny aquamarine star among
the surrounding field. Meanwhile, the stars of
spring are rising in the east. Look for the constellation
Leo, which contains the bright star Regulus,
marking the heart of the celestial lion. LEO
is home to one of the most rewarding regions
of the sky for telescope observers. The LEO triplet
features a small group of galaxies M65, M66,
and NGC 3628. Under dark skies, even modest scopes
can reveal these three distant islands floating
together in space, 35 million light -years away.
If you're feeling adventurous, try hunting down
one of the sky's most unusual deep sky objects.
The Eskimo Nebula, also known as NGC 2392, sits
in the constellation Gemini, not far from Jupiter.
This object is a planetary nebula, a glowing
shell of gas expelled by a dying star. Through
a telescope it appears as a small bluish disk,
and with larger instruments, observers often
notice a fuzzy halo that gives it the appearance
of a face framed by a parka hood, hence the nickname
the Eskimo Nebula. And somewhere far beyond the
reach of backyard telescopes, Pluto continues
its slow journey around the Sun. We actually
discussed how to view Pluto back in episode 64.
So, if you have access to a massive telescope,
a camera, and some very dark skies, go for it!
That's going to do it for this week. If you found
this episode interesting, please share it with
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Star Trails on Blue Sky and YouTube. Links are
in the show notes. Until we meet again beneath
the stars, clear skies everyone.