We're under a time crunch.
Short answer: Because we changed the definition of the word “planet” to better fit its meaning.
Is there a planet—or even planets—waiting to be discovered out there?
But we won't know until we get there.
More exciting news about cold, dead rocks
Scientists aren't just jerking you around—this is about something more than your childhood nostalgia
Imagine the space-scuba diving potential
How skeptical should we be, and how will we find out if this mystery planet is really out there?
Scientists are hot on the trail of our solar system's 9th planet
Cathy Olkin talks about what New Horizons has seen and where it's going next
Charon is the real #SuperBloodMoon in latest New Horizons pics
Short answer: It depends who you ask
The latest and greatest images from the New Horizons mission
Popular Science goes way back
New Horizons spacecraft reveals the dwarf planet is slightly larger, has polar ice cap, and more
After nine years and three billion miles, here's what we're learning from it all
New Horizons scientist Leslie Young discusses what to expect from the flyby on Tuesday, and the 28-year wait leading up to it
And he thinks the upcoming flyby will prove it
This year's missions to the outer solar system are set to shake up the planetary family tree
That's three moons down, two to go
The little white dot is only going to get bigger
What will we find when we reach Pluto and Ceres? We don't know, but it's going to be wild.
What's on the horizon for the New Horizons spacecraft