How did Pluto become a dwarf planet?

earthsky.org | 8/24/2019 | EarthSky
monna (Posted by) Level 3
Click For Photo: https://en.es-static.us/upl/2015/11/pluto-7-14-2015-backlit.jpg

Pluto backlit, via New Horizons spacecraft on July 14, 2015. Image via NASA/JHUAPL/SwRI.

August 24, 2006. Today is the 13th anniversary of the decision by the International Astronomical Union (IAU) to demote Pluto to dwarf planet status. Our solar system went from having nine major planets to having eight major planets. Pluto, once considered the outermost planet, became more widely known as the largest of a number of small bodies in the outer solar system. Neptune, the eighth large planet out from our sun, is now considered outermost major planet. The IAU formulated a new definition of what it means to be a planet. The IAU’s XXVIth General Assembly formalized the decision and announced it on August 24, 2006. The public and many astronomers didn’t take it lightly, with some declaring they would still consider Pluto a planet. The word plutoed – meaning to demote or devalue something – entered the global lexicon.

Questions - Today - Prior - Astronomers - Standards

Why did it happen? We still get questions about this today. Prior to 2006, astronomers hadn’t gotten around to establishing clear standards – such as a minimum size or mass, or other considerations – by which an object might be categorized as a solar system “planet” versus “dwarf planet.”

They began to see a need when many small bodies – such as Haumea and Makemake – began to be discovered in the outer solar system. Eris, also considered a dwarf planet, is even more massive than Pluto! So if Pluto is a planet, why shouldn’t Eris be granted planet status as well? That was the question the IAU asked itself, which led to its formation of a Planet Definition Committee and ultimately the 2006 decision.

Meet - Planet - Definition - Committee - International

Meet the Planet Definition Committee of the International Astronomical Union. This group made the final decision to demote Pluto to dwarf planet status. But, even within...
(Excerpt) Read more at: earthsky.org
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