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- [Narrator] You've seen weird,

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wonderful worlds in science fiction.

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We don't yet know what sorts
of life might exist out there.

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But some of the planets
not unlike the ones

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in your favorite stories are real.

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At NASA we're studying them.

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They're called exoplanets.

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The term exoplanet means a
planet outside our solar system,

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a planet that doesn't orbit our sun.

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Most orbit other stars,

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but some are just sunless wanders

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out in the space between the stars.

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Now, just the fact that
they orbit other stars

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means exoplanets are extremely far away.

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Most are too far to even dream

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of sending space probes to explore them.

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So we study them in other
ways, like with telescopes

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on the ground and in
space that can observe

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these far off planets from
right here in our solar system.

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Here's the thing about exoplanets.

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They are everywhere.

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In fact, from our observation so far,

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we know there are more planets than stars.

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So there's our solar system.

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Then there are all the billions

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of planetary systems in
our galaxy, the Milky Way.

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Then there are all the
billions of other galaxies.

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Basically, there are a lot
of exoplanets out there.

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Each of the stars you see
in the night sky is the sun

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for any planets that orbit around it.

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But not all stars are created equal.

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Bigger stars burn way brighter and hotter

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and don't last as long.

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Smaller, fainter stars like our sun

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and red dwarf stars last much longer.

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But even nice cool red dwarf
stars can have powerful flares

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that blast their planets with radiation.

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We're still trying to
understand which kinds

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of stars provide long
lasting stable conditions

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that could allow life
a chance to take hold

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and evolve like it did here on Earth.

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Exoplanets are super
hard to see both because

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they're so far away and because

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they're so much fainter than their stars.

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But we've worked out some
clever methods to detect them

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and even take pictures of some.

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So what can we observe?

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Well, for many, we can
determine their size,

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their mass, how much they weigh,

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and how far away from
their stars they orbit.

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From these and a few other clues,

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we can infer a bunch of other qualities

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like how hot or cold it
might be on their surfaces

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or if they even have surfaces.

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We can tell that some are
gas giants like Jupiter

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while others are like bigger
bulkier versions of Earth.

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For some, we can determine
they have atmospheres

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and even some of the gases
in those atmospheres.

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Most exoplanets are very
different from our planet.

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They have a lot of weird
wild variety with gas giants

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much bigger than our own
Jupiter and other planets

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with oceans of lava or rainy
glass or even gemstone.

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Funny thing is looking
at how they're arranged

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as families of planets, we don't see a lot

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of exoplanet systems that
look like ours so far.

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Many are arranged quite differently.

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So we might actually be the weird ones.

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Some planets are closer to their stars.

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Some are super far.

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Some even orbit multiple stars.

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Imagine having two or
three suns in the sky.

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So why do we study exoplanets?

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Well, our interest in finding worlds

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with life on them is a big factor.

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We want to know more about
what makes a planet a place

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with all the right ingredients
and conditions for life,

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what scientists refer to as habitability.

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How does it happen?

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How common is it?

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We think the most life-ready
planets are the ones

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most similar to Earth
with a range of qualities

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that include similar size
and composition to our planet

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and being at the right
distance from their stars

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to have liquid water on the surface.

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These qualities are really
challenging to observe

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from so far away, but we're working on it.

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Exoplanets teach us a
bunch of other things too.

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Studying other planetary
systems helps us better

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understand the story of
our own planet family

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including Earth.

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Scientists detected the first
exoplanets in the 1990s.

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But now we're finding tons
more, thousands so far.

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We're studying their atmospheres

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and even making weather maps for some.

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We're surveying exoplanets to
understand all their variety.

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And the more we learn, the
more it powers our curiosity,

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the more we want to explore exoplanets,

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planets outside our solar system.