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Speaker 1: Welcome to Brainstuff, a production of iHeartRadio, Hey brain Stuff

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Speaker 1: Lauren Vogelbaum here. Back in two thousand and six, to

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Speaker 1: the puzzlement of many in the non scientific public and

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Speaker 1: some astronomers as well, the International Astronomical Union decided to

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Speaker 1: demote Pluto from its status as a full fledged planet. Instead,

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Speaker 1: the IAU decided what had been considered the most distant

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Speaker 1: of the nine planets in our Solar System actually belonged

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Speaker 1: in a new category of dwarf planets. This category also

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Speaker 1: includes Series, the largest object in the asteroid belt between

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Speaker 1: Mars and Jupiter. The IAU's reasoning was that Pluto only

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Speaker 1: had two of what they had decided were the three

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Speaker 1: characteristics of a planet. That it is in orbit around

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Speaker 1: the Sun, that it has sufficient mass for its self

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Speaker 1: gravity to overcome rigid body forces and give it a

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Speaker 1: nearly spherical shape. And that it has cleared the neighborhood

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Speaker 1: around its orbit of other objects, a meaning that it's

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Speaker 1: either collided with, captured, or driven away smaller objects nearby.

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Speaker 1: Pluto flunked that last test because it shares its orbit

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Speaker 1: with the Kuiper Belt, a sort of doughnut shaped disc

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Speaker 1: of thousands of smaller icy objects beyond Neptune that Pluto

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Speaker 1: has failed to clean up gravitationally speaking, the ii used decision,

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Speaker 1: which was voted on by a very small percentage of

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Speaker 1: the world's astronomers and planetary scientists, was a controversial one.

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Speaker 1: After a debate in twenty fourteen among scientists sponsored by

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Speaker 1: the Harvard Smithsonian Center for Astrophysics, the majority of the

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Speaker 1: non expert audience voted for a simpler definition of planet,

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Speaker 1: basically that it has to be spherical, an orbit around

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Speaker 1: a star or the remnants of one. This definition included Pluto,

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Speaker 1: and that audience aren't the only people who feel this way.

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Speaker 1: In a paper published in the journal Icarus in February

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Speaker 1: of twenty nineteen, a team of planetary scientists analyzed more

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Speaker 1: than two centuries worth of scientific studies and found that,

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Speaker 1: with the exception of one paper published in eighteen oh

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Speaker 1: two by British astronomer Sir William Herschel, nobody talked about

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Speaker 1: the non sharing of an orbit as a criterion for

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Speaker 1: distinguishing planets from non planets. To the contrary, the researchers

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Speaker 1: found that scientists routinely described what we now know to

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Speaker 1: be asteroids as planets until the nineteen fifties, because that

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Speaker 1: is when our instruments became sensitive enough to show that

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Speaker 1: asteroids had geophysical differences, namely, they weren't massive enough to

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Speaker 1: be rounded. The researchers wrote in the paper, We therefore

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Speaker 1: conclude that the argument made during the IAU planet definition

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Speaker 1: controversy that planet sized Kuiper Belt objects should be classified

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Speaker 1: as non planets because they share orbits is arbit and

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Speaker 1: not based on historical precedent before the article. This episode

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Speaker 1: is based on how stuff Works. Spoke via email with

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Speaker 1: paper co author Philip Metzger, a planetary scientist at the

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Speaker 1: University of Central Florida. He explained that the ia used

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Speaker 1: emotion of Pluto largely has been disregarded by planetary scientists.

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Speaker 1: A quote in science, we classify objects in ways that

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Speaker 1: are scientifically useful. The definition that says Pluto is not

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Speaker 1: a planet is not useful because scientists are not using

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Speaker 1: it in their publications. But the definition that has existed

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Speaker 1: since the time of Galileo, the one that most planetary

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Speaker 1: scientists actually use, is very useful, and we use it

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Speaker 1: in our publications all the time. That definition from Galileo

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Speaker 1: says that the planet is a geologically complex body like

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Speaker 1: the Earth is. Pluto is most definitely a geologically complex body,

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Speaker 1: fully worthy of the term planet, as Galileo and Planeto Harry,

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Speaker 1: scientists have used the word for the past five hundred years. Moreover,

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Speaker 1: Metzger argues the IAU's definition of a planet actually was

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Speaker 1: a step backward toward a pre scientific view of nature.

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Speaker 1: He said, scientists discovered the solar system is messy, that

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Speaker 1: planets don't all orbit the Sun, that they kick each

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Speaker 1: other around and share orbits with other objects. The IAU

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Speaker 1: definition tries to emphasize the organization of a solar system,

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Speaker 1: saying planets are the small number of objects that rule

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Speaker 1: in their orbits. It communicates the wrong idea that organization

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Speaker 1: is the central truth about solar systems. In fact, for

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Speaker 1: a planet to clear its orbit, the process is contingent, incomplete,

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Speaker 1: and often temporary. A broadening or rebroadening the definition of

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Speaker 1: planets would lead the way to including other objects like Aris,

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Speaker 1: an object in the Kuiper Belt that's twenty five percent

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Speaker 1: larger than Pluto. It was discovered in two thousand in

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Speaker 1: five and prompted the debate that led to the IAU's redefinition.

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Speaker 1: A Metzker said a problem with the two thousand and

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Speaker 1: six definition is that people have lost interest in the

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Speaker 1: discovery of planets. People think, well, they are just leftover

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Speaker 1: junk like asteroids, though they're not important. As a result,

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Speaker 1: the excitement is not taught in the classroom and the

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Speaker 1: public doesn't pay attention. But they are actually amazing planets

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Speaker 1: like Pluto and Shareon, and there are over one hundred

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Speaker 1: and fifty of them, and there is plenty that's interesting

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Speaker 1: about Pluto. How stuffworks also spoke via email with paper

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Speaker 1: co author Kirby Runyan, a planetary geomorphologist at the Planetary

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Speaker 1: Science Institute. He said Pluto has glaciers sliding down from

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Speaker 1: the mountains. It has a multi layered atmosphere with climate cycles.

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Speaker 1: It has mountains as big as the Rocky Mountains and

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Speaker 1: they are currently being built up. It has an ancient

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Speaker 1: ice lake with a shoreline. It has sublimation pits in

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Speaker 1: the ice with fantastical patterns that suggest convection is happening

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Speaker 1: under the ice. There's evidence of an underground ocean. There

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Speaker 1: must be a heat source to keep that ocean liquid.

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Speaker 1: There's even a possibility that life could exist in that ocean.

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Speaker 1: There's still much to be learned about Pluto. The probe

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Speaker 1: New Horizons did a fly by in twenty fifteen, but

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Speaker 1: most of Pluto's southern hemisphere was shrouded in winter darkness

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Speaker 1: at the time, and other regions were in low resolution,

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Speaker 1: and the probe didn't include every possible piece of equipment.

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Speaker 1: For example, if there is or was a subsurface liquid ocean,

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Speaker 1: discovering a magnetic field around the planet would provide a

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Speaker 1: solid clue, but would need to send a magnetometer on

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Speaker 1: our next spacecraft to head that way. Beyond that, it's

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Speaker 1: not known whether Pluto's features are unusual or representative of

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Speaker 1: other small planets, Iranian said. For instance, are our most

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Speaker 1: Huper Belt planets simple with just craters and fractures like

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Speaker 1: the moons of Uranus or share On, or are they

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Speaker 1: dynamic planets. Triton, we think, used to be a Kuiper

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Speaker 1: Belt planet and is now a satellite planet orbiting Neptune.

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Speaker 1: It also has rich and varied act of geology, like geysers,

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Speaker 1: but of a different nature than Pluto. However, Metzger is

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Speaker 1: not hopeful that the IAU will reconsider its decision. He

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Speaker 1: said many of its members have become stubborn about it.

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Speaker 1: This is why we aren't supposed to vote in science.

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Speaker 1: Voting creates biases. Taxonomical classification is a part of science,

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Speaker 1: so we should not allow biases to enter in. That

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Speaker 1: is why it was a mistake to vote on the

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Speaker 1: definition of a planet. It should have never happened. Today's

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Speaker 1: episode is based on article Pluto is it a planet?

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Speaker 1: After all? On how stuffworks dot Com? Written by Patrick J. Kiger.

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Speaker 1: And Stuff is production of iHeartRadio in partnership with how

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Speaker 1: stuffworks dot Com and is produced by Tyler Klang. Four

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Speaker 1: more podcasts my heart Radio, visit the iHeartRadio app, Apple Podcasts,

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Speaker 1: or wherever you listen to your favorite shows.