WEBVTT

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[upbeat music]

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- "OUR WORLD."

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- YOU'VE ALL SEEN THE MOON
IN THE SKY, RIGHT?

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ALTHOUGH IT MAY NOT
LOOK THE SAME EVERY NIGHT,

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IT IS EARTH'S ONE AND ONLY MOON.

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BUT DID YOU KNOW THAT
OTHER PLANETS HAVE MOONS TOO?

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IN FACT, THERE ARE OVER
300 MOONS IN OUR SOLAR SYSTEM.

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ALL OF THE PLANETS
HAVE MOONS ORBITING THEM

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EXCEPT FOR MERCURY AND VENUS.

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THE INNER PLANETS
HAVE FEWER MOONS ORBITING THEM

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THAN THE OUTER PLANETS.

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GAS GIANTS
LIKE SATURN AND JUPITER

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HAVE OVER 50 MOONS
ORBITING EACH ONE OF THEM.

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AS ASTRONOMERS USE
BETTER AND BETTER TELESCOPES

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AND SEND OUT MORE SPACE PROBES,

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THEY CONTINUE TO FIND
EVEN MORE MOONS.

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AND THESE MOONS
COME IN ALL DIFFERENT SIZES.

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SOME MOONS ARE REALLY HUGE,
LIKE JUPITER'S MOON GANYMEDE.

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THIS MOON IS SO BIG

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THAT IT'S ACTUALLY BIGGER
THAN THE PLANET MERCURY.

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OTHER MOONS ARE REALLY SMALL,
LIKE MARS' MOON DEIMOS.

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IT'S ONLY 12 KILOMETERS
IN DIAMETER.

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SOME MOONS,
LIKE JUPITER'S EUROPA,

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ARE REALLY INTERESTING
TO SCIENTISTS AND RESEARCHERS.

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HERE'S DR. JAMES GREEN,

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DIRECTOR OF PLANETARY SCIENCES
AT NASA,

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TO TELL US A LITTLE BIT
ABOUT EUROPA.

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- WELL, WHAT'S ON THE SURFACE
OF EUROPA IS ICE.

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SO WHAT HAPPENS
TO THE ICE OF EUROPA?

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THE PULL THAT JUPITER
PUTS ON EUROPA

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EVAPORATED THE ICE AWAY,

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AND YOU'RE LITERALLY LOOKING
AT WHAT'S LEFT.

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BUT WHAT IT'S DOING
IN THE INSIDE

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IS MELTING THE ICE.

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WE NOW KNOW
THERE'S MORE WATER ON EUROPA

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THAN THERE IS ON THIS PLANET.

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- COOL.

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I LEARNED HOW SMALL OBJECTS
IMPACT BIG OBJECTS IN SPACE

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AND LEAVE HUGE CRATERS,
LIKE THOSE FOUND ON OUR MOON.

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THAT'S THE SAME REASON
SATURN'S MOON MIMAS

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HAS A HUGE CRATER
ON ITS SURFACE.

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AND LOOK AT ALL THE CRATERS
ON JUPITER'S MOON CALLISTO.

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SATURN'S MOON TITAN HAS REALLY
MADE RESEARCHERS CURIOUS.

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HERE'S DR GREEN AGAIN
TO TELL US MORE.

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- BUT WITH CASSINI, THESE ARE
THE IMAGES WE'RE BRINGING BACK.

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THESE REGIONS,
THESE DARK REGIONS,

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WE NOW KNOW ARE LIQUID.

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TITAN IS THE ONLY OTHER OBJECT
BESIDES THE EARTH

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IN OUR SOLAR SYSTEM
THAT HAS LIQUID ON ITS SURFACE.

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AND THAT LIQUID IS NOT WATER.

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IT IS METHANE AND ETHANE.

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IT'S A COMPLETELY
DIFFERENT WORLD.

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AND IN FACT, RIGHT NOW, TODAY,
IT IS RAINING METHANE

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IN THE SOUTHERN HEMISPHERE
OF TITAN.

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IT HAS A HYDROLOGICAL CYCLE
MUCH LIKE THE EARTH

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OF EVAPORATION,
CONDENSATION, RAIN.

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THAT CYCLE
THAT WE'RE SO FAMILIAR WITH

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IS GOING ON RIGHT NOW
IN THIS MOON TITAN.

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- RAIN ON A MOON?

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I THOUGHT THAT ONLY HAPPENED
ON EARTH.

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AND WHAT ABOUT ENCELADUS?

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I HEARD THAT'S ANOTHER
REALLY COOL MOON OF SATURN.

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- AND WHEN WE LOOK
AT ENCELADUS CLOSELY,

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WE FIND
IN THE SOUTHERN HEMISPHERE

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HUGE GEYSERS OF WATER
BEING POURED OUT.

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IS THAT COMING
FROM AN UNDERGROUND OCEAN?

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IS IT COMING FROM A LAKE?

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WHAT IS THE PROCESS
THAT DOES THAT,

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AND IS THERE POTENTIAL FOR LIFE
EVEN ON THIS DISTANT REGION

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SO, SO VERY FAR AWAY
FROM THE EARTH?

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- WOW, THERE MIGHT EVEN BE LIFE
ON ONE OF SATURN'S MOONS.

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WHO KNEW THERE COULD BE RAIN
OR VOLCANOES OR ICE

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OR MAYBE EVEN LIQUID WATER

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ON THESE MOONS
IN OUR SOLAR SYSTEM?

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I THINK THE MOONS
ARE JUST AS INTERESTING

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AS THE PLANETS ARE.

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WHO KNOWS WHAT ELSE
WE'LL FIND OUT ABOUT THEM?

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HEY, DON'T GET LEFT BEHIND.

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YOU CAN FOLLOW THE NASA MISSIONS
TO OTHER WORLDS

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BY VISITING
NASA'S SOLAR SYSTEM WEBSITE.

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AND THE NEXT TIME
YOU LOOK UP AT THE NIGHT SKY,

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JUST REMEMBER
THAT SOME OF THE THINGS

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YOU CAN SEE FROM OUR WORLD

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JUST HAPPEN TO BE MOONS
ORBITING OTHER PLANETS.

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- "OUR WORLD."