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(SCIENCE TREK MUSIC)

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JOAN CARTAN-HANSEN, HOST: To 
understand more about

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exoplanets, you first should 
know what a planet is.

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You would think this is an easy 
question to answer,

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but it isn't.

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Scientists have been arguing 
about this for years.

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The current definition of a 
planet is: A body or object that

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orbits a star and not a 
different planet.

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It must be big enough to have 
enough gravity to force it into

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a spherical shape and it must be 
big enough that its gravity has

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cleared away any other objects 
of a similar size

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near its orbit.

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Everything else in our solar 
system except satellites are

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called small solar 
system bodies.

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Our solar system has 8 planets.

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Dwarf planets like Pluto, dozens 
of moons and millions of

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asteroids, comets and 
meteoroids.

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Now an exoplanet is any planet 
beyond our solar system.

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Most are tied to other stars but 
there are free-floating or rogue

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exoplanets.

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We've learned some exoplanets 
are a bit weird.

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Some are entirely covered by 
water, some are covered by

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oceans of lava, and some may 
have atmospheres that rain

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rubies or glass.

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For more information about 
exoplanets, check out the

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Science Trek website.

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You'll find it at 
ScienceTrek.org.