Nasa may revisit one of outer space’s thorniest questions ...

Add Yahoo as a preferred source to see more of our stories on Google. Guests visting the Lowell Observatory in Flagstaff, Arizona during the I Heart Pluto Festival gaze at celestial objects from the ...

Pluto was downgraded from a planet to a dwarf planet in 2006 by the International Astronomical Union. The main reason for Pluto's demotion is that it's not able to "clear its orbit of debris." Other ...

Two decades ago, the International Astronomical Union—which defines and names celestial bodies—redefined the criteria for ...

Pluto, discovered 90 years ago on Feb. 18, 1930, was long considered the solar system's ninth planet. Although small, it orbits the sun and has the spherical shape required to be considered a planet.

For no explainable practical reason, humans are enamored with – and even empathetic toward – specific inanimate objects. Our first car. A choice coffee mug. And for a particular subset of the ...