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When the International Astronomical Union ( IAU ) bump Pluto from a planet to a dwarf planet in 2006 , it storm a lot of people , including some scientist . Even many years afterward , some astronomers want torevise the definition of a planetto clarify the parameters that set up planets apart from other celestial objects .
But why is n’t Pluto moot a planet anymore ? It starts with the definition of a planet — or miss thereof . Before 2006 , there were n’t strict criteria for a satellite . Instead , planetswere broadly regardedas object larger than asteroids that orbit the sun . In the mid-1800s , for example , more than a dozen aim that we now see as asteroid were considered to be planets .
An image of Pluto captured by NASA’s New Horizon spacecraft in 2015.
When did Pluto become a planet?
When Pluto was light upon byClyde Tombaughin 1930 , scientists were searching far and panoptic for an strange celestial body to excuse some irregularity in Uranus ' orbit . Tombaugh , a new minted stargazer at Lowell Observatory in Arizona , was tasked with identifying the culprit . After several months , he successfully place a round , rough object beyond Uranus that he consider might contribute to its orbital wobble . It would finally be named Pluto after the Roman god of the Scheol . Despite being smaller than several know moons , it was deemed large enough to be considered a planet .
However , it soon became unmistakable that Pluto was not big enough to exert the kind of gravitational pull necessary to regulate Uranus ' orbit . What ’s more , in the 1990s , astronomers key out that Pluto was surround by a number of likewise sized objects ; it belong to a region of thesolar systemlater nominate the Kuiper Belt .
This sparked debate about Pluto ’s status in the planetary canon , which came to a head at a 2006 coming together in Prague .
Pluto is located in the Kuiper Belt, far from the sun. Thousands of known objects orbit there, meaning Pluto is not the gravitationally dominant body in the region.
Why is Pluto not considered a planet?
That yr , the IAU tasked a small commission with make a solve definition of a " major planet . " They land onthree criterion :
Based on the third necessity , the committee declared that Pluto no longer dependent as a planet because of its position in the littered Kuiper Belt , where thousands of object seat beyond the orbit of Neptune . Pluto , therefore , is not the gravitationally dominant object in its neighborhood — and thus , not a planet , agree to the novel definition .
Related : When will Pluto complete its first orbit since its discovery ?
But this framework draw immediate criticism . " That definition is distinctly short , because it exclude exoplanets , " or planets see beyond our solar system , Jean - Luc Margot , a planetary scientist at UCLA , enjoin Live Science . It is also super difficult to determine when a physical structure has cleared its own orbit , he said — Pluto clearly has n’t , but by some definition , neither has Mars .
— James Webb Space Telescope deciphers the origins of Pluto ’s frosty lunar month Charon
— Pluto ’s immense white ' bosom ' has a amazingly vehement origin , new study suggests
— Pluto may have an glass - spewing ' supervolcano ' the size of Yellowstone , New Horizons datum reveals
Pluto ’s demotion remainscontroversialfor some scientist , though , in part because of the way it was reclassified . Philip Metzger , a planetary physicist who worked onNASA ’s New Horizons mission to Pluto , has previously pointed outthat the IAU did not put their definition of a major planet up for a vote from the larger scientific biotic community . In his horizon , that makes the new definition invalid . And for others , it ’s a matter of sentiment — many the great unwashed grow up thinking of Pluto as a satellite , and they are still emotionally commit in it .
disregarding of whether Pluto is a major planet or a dwarf planet , it remains a fascinating part of the solar system , from itshuge white " substance " of frozen nitrogento theice - retch ' supervolcano’thought to lurk below its control surface .
" Pluto has n’t changed , " Margot said . " It ’s just as exciting . "
