How Do We Know?
An observatory dome slit open to a single bright star.

A star can dim.

How do we find a planet we cannot see?

A steady star. Tap the picture. What happens if something passes?Diagram · Something else changed

The evidence is what the star does.

A tug. A dimming. A beat that repeats. One effect can have more than one cause.

An unseen thing can show itself by what it does.

Keep looking

There is more in this room, if you want it.

Something else changed · Evidence strongly supports this

What else would you want to check?

A Match Is Not Enough