Wednesday, July 7, 2021

We want Pluto back!

It may not be considered a planet anymore, but Pluto is still as interesting as the planets that orbit our central star. Up until 2015, Pluto was largely a mystery. We had no clear images of its surface, and so things like it’s geology and past were pure speculation. Then in the summer of 2015, NASA’s New Horizons spacecraft became the first spacecraft to successfully fly through the Pluto system, taking the highest resolution images of its surface to date. New Horizons revealed an absolutely stunning world, one with vast nitrogen ice plains, mountains made of ice, canyons, and evidence of past volcanism. There’s even some evidence that liquid nitrogen flows on the surface. 

So why is a world so interesting not considered to be a planet anymore? In 2006, astronomers classified Pluto as a dwarf planet, and to this day, people still debate whether or not that was a good decision. Changing the classification of a world says nothing about what that world is like, and so regardless of what we think Pluto is, it’s still an interesting world worth visiting again in the future. The reasons behind the 2006 decision have to do with other worlds that were discovered in the solar system. In 2005, astronomers discovered another small world called Eris, also located in the Kuiper Belt. Astronomers classified Eris as a dwarf planet, yet it was actually more massive than Pluto. Eris ignited a debate on whether or not these small worlds should be considered planets, or if they should all be classified as dwarf planets. Then in 2006, astronomers devised a definition of what a planet is. In order to be a planet, a world must fit three criteria. First, it must orbit the sun. Second, it must have a strong enough gravitational pull so as to become spherical in shape. Third, it must have a strong enough gravitational pull to clear its orbital path of debris. Although Pluto meets the first two criteria, it does not meet the last one. Unfortunately, Pluto’s gravity is too weak to clear its orbital path of debris, and so Pluto was downgraded to dwarf planet. 

Image credit: NASA, New Horizon 

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