Pluto

New Horizons principal investigator Alan Stern discusses the mission and its Jan. 1 flyby of the mysterious, distant object Ultima Thule.

There's something weird going on with Ultima Thule, the distant object that NASA's New Horizons spacecraft will fly by just 10 days from now.

NASA's history-making New Horizons spacecraft may not be done with deep-space flybys after its highly anticipated New Year's Day encounter.

The free Pluto Safari app let New Horizons fans track the probe's flyby of Pluto in 2015, and now it's set to follow the journey past the distant body Ultima Thule on New Year's Day.

NASA's New Horizons spacecraft will indeed get very close to the mysterious, distant object Ultima Thule on New Year's Day.

NASA's New Horizons probe is getting set for the farthest-out flyby in history, and you can send some words of encouragement to help the spacecraft get across the finish line.

The small object Ultima Thule swims amid a sea of distant stars in a new photo captured by NASA's approaching New Horizons around midnight EST (0500 GMT) on Dec. 1.

A spacecraft orbiting the dwarf planet could use Pluto's moon Charon to make important orbital changes.

In less than 10 weeks, NASA's New Horizons spacecraft will explore the most distant target ever visited by a spacecraft. Mission team members don't know what to expect — and that's part of the fun.

Evidence of a big, unseen world in the extreme outer solar system continues to mount, giving astronomers more and more confidence that "Planet Nine" is real.

NASA's New Horizons spacecraft successfully completed a brief engine burn on Oct. 3, the first maneuver in which it was able to rely on actual photographs it had already taken of its eventual target.

NASA's New Horizons team has passed its 'final exam' ahead of the probe's Jan. 1 flyby of the distant object dubbed Ultima Thule.

Scientists have spent 12 years arguing over how to classify Pluto, and a recently published paper offers a new — but surprisingly old — reason for restoring the object's planetary status.

With books about space and science intended for a young audience, there is a fine line between writing that's too complex and writing that older kids might write off as "babyish."

"Ask a Spaceman" is live for the first time on Facebook — and astrophysicist Paul Sutter jumps right into it with a trip to Pluto.

There's a vast "hydrogen wall" at the edge of our solar system, and NASA scientists think their New Horizons spacecraft can see it.

The handlers of NASA's New Horizons spacecraft are gearing up for one last shadow-chasing adventure.