“New Horizons shattered a major paradigm of planetary science,” says Alan Stern, the mission’s principal investigator. “Pluto ...

Feb. 18 marks the 95th anniversary of the discovery of our outermost planet-not-planet. Here's what to know about the short ...

I require roughly 19 conditions to be exactly perfect to have any real chance of getting a good night’s sleep. First, there’s ...

The number of planets that orbit the sun depends on what you mean by “planet,” and that’s not so easy to define ...

In August 2006, the International Astronomical Union made the controversial, but correct, decision to demote Pluto from its ...

Scientists at NASA for the first time have been able to observe the make up of Pluto and other small and icy celestial bodies ...

Trans-Neptunian objects (TNOs) are icy bodies that vary widely in size, from large dwarf planets like Pluto and Eris—each ...

Early observations hinted that Eris might be bigger than Pluto, whose own size remained uncertain until the New Horizons spacecraft flew past in July 2015. But whether larger or smaller than Pluto ...