Is Pluto Really Not a Planet?

Although the International Astronomical Union demoted Pluto from a planet to a dwarf planet in 2006, some scientists think it deserves to be reinstated. Learn why in this episode of BrainStuff, based on this article: https://science.howstuffworks.com/pluto-is-it-planet-after-all.htm

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Episode Transcript

Speaker 1 (00:01):
Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff
Lauren Vogelbaum here. Back in two thousand and six, to
the puzzlement of many in the non scientific public and
some astronomers as well, the International Astronomical Union decided to
demote Pluto from its status as a full fledged planet. Instead,

(00:24):
the IAU decided what had been considered the most distant
of the nine planets in our Solar System actually belonged
in a new category of dwarf planets. This category also
includes Series, the largest object in the asteroid belt between
Mars and Jupiter. The IAU's reasoning was that Pluto only

(00:44):
had two of what they had decided were the three
characteristics of a planet. That it is in orbit around
the Sun, that it has sufficient mass for its self
gravity to overcome rigid body forces and give it a
nearly spherical shape. And that it has cleared the neighborhood
around its orbit of other objects, a meaning that it's
either collided with, captured, or driven away smaller objects nearby.

(01:10):
Pluto flunked that last test because it shares its orbit
with the Kuiper Belt, a sort of doughnut shaped disc
of thousands of smaller icy objects beyond Neptune that Pluto
has failed to clean up gravitationally speaking, the ii used decision,
which was voted on by a very small percentage of
the world's astronomers and planetary scientists, was a controversial one.

(01:35):
After a debate in twenty fourteen among scientists sponsored by
the Harvard Smithsonian Center for Astrophysics, the majority of the
non expert audience voted for a simpler definition of planet,
basically that it has to be spherical, an orbit around
a star or the remnants of one. This definition included Pluto,

(01:57):
and that audience aren't the only people who feel this way.
In a paper published in the journal Icarus in February
of twenty nineteen, a team of planetary scientists analyzed more
than two centuries worth of scientific studies and found that,
with the exception of one paper published in eighteen oh
two by British astronomer Sir William Herschel, nobody talked about

(02:18):
the non sharing of an orbit as a criterion for
distinguishing planets from non planets. To the contrary, the researchers
found that scientists routinely described what we now know to
be asteroids as planets until the nineteen fifties, because that
is when our instruments became sensitive enough to show that
asteroids had geophysical differences, namely, they weren't massive enough to

(02:43):
be rounded. The researchers wrote in the paper, We therefore
conclude that the argument made during the IAU planet definition
controversy that planet sized Kuiper Belt objects should be classified
as non planets because they share orbits is arbit and
not based on historical precedent before the article. This episode

(03:05):
is based on how stuff Works. Spoke via email with
paper co author Philip Metzger, a planetary scientist at the
University of Central Florida. He explained that the ia used
emotion of Pluto largely has been disregarded by planetary scientists.
A quote in science, we classify objects in ways that
are scientifically useful. The definition that says Pluto is not

(03:29):
a planet is not useful because scientists are not using
it in their publications. But the definition that has existed
since the time of Galileo, the one that most planetary
scientists actually use, is very useful, and we use it
in our publications all the time. That definition from Galileo
says that the planet is a geologically complex body like

(03:51):
the Earth is. Pluto is most definitely a geologically complex body,
fully worthy of the term planet, as Galileo and Planeto Harry,
scientists have used the word for the past five hundred years. Moreover,
Metzger argues the IAU's definition of a planet actually was
a step backward toward a pre scientific view of nature.

(04:14):
He said, scientists discovered the solar system is messy, that
planets don't all orbit the Sun, that they kick each
other around and share orbits with other objects. The IAU
definition tries to emphasize the organization of a solar system,
saying planets are the small number of objects that rule
in their orbits. It communicates the wrong idea that organization

(04:36):
is the central truth about solar systems. In fact, for
a planet to clear its orbit, the process is contingent, incomplete,
and often temporary. A broadening or rebroadening the definition of
planets would lead the way to including other objects like Aris,
an object in the Kuiper Belt that's twenty five percent
larger than Pluto. It was discovered in two thousand in

(05:00):
five and prompted the debate that led to the IAU's redefinition.
A Metzker said a problem with the two thousand and
six definition is that people have lost interest in the
discovery of planets. People think, well, they are just leftover
junk like asteroids, though they're not important. As a result,
the excitement is not taught in the classroom and the

(05:22):
public doesn't pay attention. But they are actually amazing planets
like Pluto and Shareon, and there are over one hundred
and fifty of them, and there is plenty that's interesting
about Pluto. How stuffworks also spoke via email with paper
co author Kirby Runyan, a planetary geomorphologist at the Planetary

(05:42):
Science Institute. He said Pluto has glaciers sliding down from
the mountains. It has a multi layered atmosphere with climate cycles.
It has mountains as big as the Rocky Mountains and
they are currently being built up. It has an ancient
ice lake with a shoreline. It has sublimation pits in
the ice with fantastical patterns that suggest convection is happening

(06:04):
under the ice. There's evidence of an underground ocean. There
must be a heat source to keep that ocean liquid.
There's even a possibility that life could exist in that ocean.
There's still much to be learned about Pluto. The probe
New Horizons did a fly by in twenty fifteen, but
most of Pluto's southern hemisphere was shrouded in winter darkness

(06:27):
at the time, and other regions were in low resolution,
and the probe didn't include every possible piece of equipment.
For example, if there is or was a subsurface liquid ocean,
discovering a magnetic field around the planet would provide a
solid clue, but would need to send a magnetometer on
our next spacecraft to head that way. Beyond that, it's

(06:51):
not known whether Pluto's features are unusual or representative of
other small planets, Iranian said. For instance, are our most
Huper Belt planets simple with just craters and fractures like
the moons of Uranus or share On, or are they
dynamic planets. Triton, we think, used to be a Kuiper
Belt planet and is now a satellite planet orbiting Neptune.

(07:14):
It also has rich and varied act of geology, like geysers,
but of a different nature than Pluto. However, Metzger is
not hopeful that the IAU will reconsider its decision. He
said many of its members have become stubborn about it.
This is why we aren't supposed to vote in science.
Voting creates biases. Taxonomical classification is a part of science,

(07:38):
so we should not allow biases to enter in. That
is why it was a mistake to vote on the
definition of a planet. It should have never happened. Today's
episode is based on article Pluto is it a planet?
After all? On how stuffworks dot Com? Written by Patrick J. Kiger.

(08:00):
And Stuff is production of iHeartRadio in partnership with how
stuffworks dot Com and is produced by Tyler Klang. Four
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