Pluto – which is smaller than Earth’s Moon – has a heart-shaped glacier that’s the size of Texas and Oklahoma. This fascinating world has blue skies, spinning moons, mountains as high as the Rockies, and it snows – but the snow is red.
On July 14, 2015, NASA’s New Horizons spacecraft made its historic flight through the Pluto system – providing the first close-up images of Pluto and its moons and collecting other data that has transformed our understanding of these mysterious worlds on the solar system’s outer frontier.
In the years since that groundbreaking flyby, nearly every conjecture about Pluto possibly being an inert ball of ice has been thrown out the window or flipped on its head.
“It’s clear to me that the solar system saved the best for last!” said Alan Stern, New Horizons principal investigator from the Southwest Research Institute, Boulder, Colorado. “We could not have explored a more fascinating or scientifically important planet at the edge of our solar system. The New Horizons team worked for 15 years to plan and execute this flyby and Pluto paid us back in spades!”
In 2006 the International Astronomical Union (IAU) demoted the much-loved Pluto from its position as the ninth planet from the Sun to one of five “dwarf planets.” The IAU had likely not anticipated the widespread outrage that followed the change in the solar system’s lineup. When the announcement was made (and even over 10 years later), people around the world objected to the planet’s demotion on principle, saying that it altered tradition and history, rather than engaging with the scientific reasoning. So, what was the IAU’s reason for demoting Pluto when it did? Why is Pluto no longer a planet?
Before the resolution in 2006, the term planet had no working definition and was based on classification from before some of the major modern discoveries within the universe that were made possible by advances in technology. To many citizens of Earth, the demotion of Pluto felt like a break from tradition, and it was precisely that—a positive step forward into a new light, new knowledge, and changing perspectives of the universe.
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