Should Pluto Regain Its Coveted Status as a Genuine Planet?

It comes with a big catch.
Brad Bergan
Pluto, the dwarf planet.dottedhippo / iStock

The way we talk about science is constantly evolving.

This is why a team of researchers has bolstered a body of ideas that proposes to do the unthinkable. The unconscionable. Grant Pluto back its planet-hood, because the criteria that canceled its planetary status may not be based on scientific ground, according to a recent study published in the journal Icarus.

While this is a cause for hope to hardcore Pluto enthusiasts, it might come at a bizarre price: a need to think of moons as planets, too.

To add Pluto, we might have to add the moon

The definition of the word "planet" is strictly regulated by the International Astronomical Union (IAU). But this isn't to say it's permanent and unchanging. It's been drafted, modified, and was last assigned a rigid meaning in August 2006. According to that definition, an astronomical body qualifies as a planet if it has enough mass to take a spherical shape, and has cleared out the local neighborhood in its orbit. And under these criteria, there are only eight planetary bodies in our solar system: the classic Mercury, Venus, Earth, and Mars, along with the gas giants Jupiter, Saturn, Uranus, and Neptune. Obviously, this leaves out our tiny friend, Pluto. And a lot of people weren't happy about it. Even some scientists responded to the IAU's move by suggesting the definition be expanded to focus on the physical properties of the body under consideration.

And now a recent paper has bolstered the case for rethinking the way we classify bodies, arguing that the old ways aren't really based on science but folklore and astrology. In case you missed it, neither of those are based on empirical evidence, and therefore do not describe an objective reality independent of observation (mainly, because they can't be falsified). And the recent study, which went forward under the leadership of Planetary Scientist Phillip Metzger of the University of Central Florida, saw researchers argue that the definition should go back to basics, and focus on one, crucial factor: that the cosmic body in question is, or has been, geologically active. This would put Pluto back on the roster, but it also comes with a very bizarre caveat.

Scientific consensus continually reshapes the way we study the universe

The proposed standard would define many bodies in the solar system as a planet, including our moon, and many other moons, dwarf planets, and even asteroids. This argument of an overextended definition has been used before to quell dissent with the current system. But the fact that these other bodies possess enough similar features to be grouped is to many a compelling reason to consider expanding the definition, argue the researchers. "It's like defining 'mammals,'" said Metzger in a blog post shared on the University of Central Florida's website. "They are mammals whether they live on the land or in the sea. It's not about their location. It's about the intrinsic characteristics that make them what they are."

For five years, the team executed an in-depth analysis of the last 400 years of scientific literature on planets, and discovered that the definition made by Galileo in the 1630s has been chipped away, little by little. The famous Renaissance Man argued that planets are simply objects made of elements that are changed through time, just like on Earth. The researchers of the recent study interpreted this to mean geological activity. Another condition set out by Galileo was that planets must merely reflect sunlight, instead of generating their own. The man's definition continued until the 20th century, when, after Pluto was discovered and interest in planetary science dropped off, "the transmission of the pragmatic taxonomy that had come down from Galileo got interrupted." While we can't say for sure if Pluto will ever regain its previous status as a planet from the IAU, it's studies like Metzger and his colleagues' that show us how much definitions and scientific consensus shape the way we observe, theorize, and think about our universe on surprisingly fundamental levels.

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