From the brains behind brains on, this is the moment of um.

Um, um, um, um, um, um, um, um,

Moment of Um comes to you from APM Studios. I'm Nico Gonzalez Whistler.

Um.

Listen up, everybody. I've done it. I have achieved memory mastery.

My very excellent mother jumps, skateboards until night time.

Get it? Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. Each word starts with the same letter as a planet,

so I can remember all eight of them. Wait, there are eight planets in space, right? Or maybe there's

more? My friend Ray wanted to know this too.

How many planets are there in space?

This is a really great question,

and it's a question that astronomers have had to try and answer

over and over again, and the answer keeps changing. My name is Mark Poppanchuk. I'm a graduate

student at the CUNY Graduate Center and at the American Museum of Natural History. We think about the

planets in our solar system. We think about Jupiter. We think about Earth, Venus, Mars, all the rest.

They're pretty interesting.

But there's this field, what are called exoplanets, which are planets around other stars.

So the ones that we know the names of, Jupiter, Saturn, Venus, those are all around our sun.

These are planets around other stars.

When I was born, there were no known

planets around other stars. But then in 1995, they found the first planet around a sun-like star.

And since then, we have now found 5,000 exoplanets. That doesn't mean there's only 5,000. It's actually really hard to find

...