Saved on this device

Follow your curiosity

What discovery has been shared with you?

FACTREE gives you something interesting to discover every day — and something worth talking about together.

Start with one fact. Explore it, go deeper, then follow whichever branch catches your imagination.

Choose subjects for a surprise

Exploring any topic

Begin your discovery

Your next discovery is one click away.

Choose one or more subjects above, or leave Any Topic selected and let curiosity decide.

Astronomy

Using Gravitational Microlensing to Detect Free-Floating Planets

Quick fact

In 2011, astronomers announced the discovery of free-floating planets using microlensing; surprisingly, their study suggested there may be nearly twice as many rogue planets as stars in our galaxy, though later analyses have revised this estimate.

Why this is interesting

Imagine a planet drifting alone in the darkness of space, invisible to every telescope. How could we ever know it's there? Astronomers use the gravity of that dark world as a lens to catch a glimpse of it.