He called this hypothetical world "Planet X." "In some ways, Pluto's more of a planet than some of the other established planets, like Mercury." ...

so much so that I know planetary scientists who call Pluto ‘the other Red Planet.’” Lon Tweeten for TIME None of the new discoveries about Pluto would have been made, of course, had the ...

And then he’d go back later and use the blink comparator to compare the photos ... that led to the discovery of Planet X. Pluto never really fit in with the other planets in the solar system.

If you answered ... of the other objects in its neighborhood. Because Pluto did not fit the last of these requirements, after years of debate it was "demoted" to the status of a dwarf planet ...

Being heartbroken for 2 months fades in comparison ... into Pluto at a slanted angle, rather than head-on. “Pluto’s core is so cold that the (rocky body that collided with the dwarf planet ...

For one reason or another, some people are still upset about Pluto's demotion from planet to dwarf planet. This demotion, by the way, occurred all the way back in 2006. So, what does famed ...

The International Astronomical Union reclassified Pluto as a dwarf planet because it does not clear its orbit of other debris. Pluto was the little planet that could — until it couldn’t.

Viewed in this longer context, the previously modern idea of having nine planets, which came about in the 1960s and lasted only until 2006, was a blip on the screen. And if you are still a Pluto ...