Once, a gassy envelope of hydrogen and helium surrounded our infant world. Over millions of years, that atmosphere escaped into space. Pluto is the only place in the solar system where we can ...

Pluto is just 1,400 miles wide, about half the width of the U.S. "It definitely kind of broke the mold," van Belle said. "In our inner solar system, we have the four terrestrial rocky planets ...

and Vesta as full-fledged members of our planetary system. Today, when tens of thousands of minor planets have been discovered (most residing in an "asteroid belt" between Mars and Pluto), not ...

Almost 10 years ago, a NASA spacecraft was able to take several photos of Pluto, known for decades as a planet before it was ...

Our solar system is probably on the mild side compared ... mission called New Horizons that will send an unmanned probe past Pluto and its five known moons in July 2015. From there Stern hopes ...

Pluto isn’t the only dwarf planet in our solar system's outer reaches. Now is an ideal time to look for the egg-shaped Haumea, says Abigail Beall ...

Pluto, our sun's most remote and mysterious planet, may once a satellite of Neptune. Current theories about its origin provide new clues to the genesis of the solar system ...

Best known for driving demotion of Pluto to dwarf planet, astronomer Mike Brown discusses the next horizons in our solar system, including the hunt for the elusive Planet 9. This article was ...

The first time you may have heard the term ‘dwarf planet’ was when Pluto got demoted to one in 2006 (RIP). However, we actually have six in our Solar System. Pluto, Ceres, Makemake ...