• NASA administrator, Jim Bridenstine, who has no background in science, said he believes Pluto is a planet.
  • Pluto was considered a planet through the early 90s, but then scientists discovered Eris, Pluto's twin, along with other nearby objects.
  • These new worlds looked and behaved like Pluto, but they were completely different from every other planet in our solar system. So astronomers created a new definition of what makes a planet a planet.
  • In 2006, the International Astronomical Union decided to reclassify Pluto as a dwarf planet, to the fury and confusion of the American public.
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NASA administrator, Jim Bridenstine, who has no background in science, said he believes Pluto is a planet.

Back in the '90s, most people took Pluto for granted. But fast forward to 2005, and scientists discovered Eris, Pluto's twin, along with other nearby objects.

These new worlds looked and behaved like Pluto, but they were completely different from every other planet in our solar system. So astronomers created a new definition of what makes a planet a planet.

In 2006, the International Astronomical Union decided to reclassify Pluto as a dwarf planet, to the fury and confusion of world.

Some people were so angry, they were giving astronomers death threats.

“People were so angry that they said that all the astronomers should be put on the wall and shot at,” said Thierry Montmerle, former general secretary for the International Astronomical Union.

Montmerle is from the same organisation of the world's astronomers that changed Pluto's status from planet to dwarf planet in 2006. And today, over 12 years later, people still have strong opinions whenever you ask: Should Pluto be a planet again?

 “In planetary science, where the experts in planets are, we call small planets "planets." We call large moons "planets." We call all the planets around other stars "planets." And the astronomer's definition wouldn't allow any of those to be planets,” said Alan Stern, who leads NASA's New Horizons mission, which flew by Pluto in 2015.

By the late '90s, it was becoming clear that Pluto wasn't alone. Astronomers had discovered other worlds in the same region, called the Kuiper belt. And some of them looked awfully like Pluto. Then in 2005, astronomers discovered Eris, which estimates at the time suggested was even larger than Pluto.

While these new worlds looked and behaved like Pluto, they were completely different from every other planet in our solar system. Something had to be done. It was clear that astronomers were in need of something they never had before: a good definition for what makes a planet a planet. So in the wake of these new discoveries, the IAU came up with a checklist.

A planet must orbit the sun, have a nearly round shape, and have cleared its neighbourhood, meaning no other large objects are nearby. And that last requirement boots Pluto off Team Planet.

Yes, Pluto orbits the sun. Yes, it's spherical. But Pit isn't always the dominant gravitational force in its neighbourhood. For one thing, Eris shares the region and isn't stuck in Pluto's orbit.

The end result? Pluto is bumped from "planet" to "dwarf planet."

Everyone's using the planetary scientist's definition in the written, refereed scientific literature. And using it at the podium in giving scientific presentations. That's the kind of consensus that's very powerful in science.

EDITOR'S NOTE: This video was originally published on June 14, 2019. Compiled by Jay Caboz. 

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