It's a small world after all, because today, we're shrinking Earth to the size of Pluto. But if our planet was this tiny, how would it alter the atmosphere? Why would the Earth get hotter? And how ...

Pluto's days, though they drag on a bit at around 153 hours, are nothing compared to its years. Pluto's orbit takes 248 Earth ...

What was discovered in Flagstaff, Arizona, and killed off in Prague? If you answered "Pluto's planethood," your grasp of the astronomical is excellent. Feb. 18 marks the 95th anniversary of the ...

The planet Neptune wobbled in its orbit around the Sun. That could only mean one thing, astronomers said: There was a ninth planet out there, somewhere, lurking in the fringes of the solar system.

Discovered in 1930, Pluto is a complex and mysterious world with mountains, valleys, plains, craters, and glaciers. Here are ...

Clyde Tombaugh noticed a speck of light that was Pluto in 1930. — -- Clyde Tombaugh is finally getting to visit the speck of light he spotted at the edge of the solar system in 1930. New Horizons ...

(Correction: An earlier version of this story misstated how far Pluto is from the sun. The correct number is 3.7 billion miles.) What was discovered in Flagstaff, Arizona, and killed off in Prague? If ...