WEBVTT

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[rocket rumbling]

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[percussive music]

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- HEY, WELCOME
TO "NASA LAUNCHPAD."

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I'M YOUR HOST,
AUDREY STAPLES.

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SO WHAT'S ONE OF THE MAIN
REASONS THAT NASA RESEARCHERS

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ARE SO EXCITED THESE DAYS?

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WELL, WE'RE TALKING ABOUT WATER.

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SURE, WATER'S A BIG PART OF LIFE
HERE ON EARTH,

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A HUGE PART, ACTUALLY.

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BUT IT'S NOT AS COMMON
ON OTHER BODIES

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THROUGHOUT OUR SOLAR SYSTEM.

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SO WHETHER WE'RE TALKING
ABOUT THE WATER ICE

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THAT THE MARS PHOENIX LANDER
DISCOVERED

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OR, MORE RECENTLY,
THE WATER ICE

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KICKED UP BY LCROSS
ON THE MOON,

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NOW'S A GOOD TIME
TO START THINKING

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ABOUT WHAT WE CAN USE
THAT WATER ICE FOR.

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WHAT WOULD I DO WITH IT?

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START PACKING IT UP

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AND FLINGING SOME MARTIAN
AND LUNAR SNOWBALLS.

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BUT I'VE BEEN TOLD, I CAN'T
MAKE A SNOWBALL ON MARS

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OR ON THE MOON,
FOR THAT MATTER,

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OR ANYWHERE ELSE WE KNOW OF
EXCEPT EARTH.

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BUT WHY NOT?

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WELL, LET'S IGNORE THE FACT
THAT I'M NOT AN ASTRONAUT,

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SO I WON'T BE LEAVING EARTH
ANYTIME SOON.

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THERE ARE TWO MAIN REASONS

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WHY SNOWBALLS
CAN ONLY BE MADE ON EARTH:

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SO LET'S EXPLORE THESE REASONS
A BIT FURTHER.

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AND FOR THAT, LET'S TALK
TO DR. PETER WASILEWSKI

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OF NASA GODDARD
SPACE FLIGHT CENTER.

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- LIFE ON EARTH
AND ALL ITS SEASONS IS,

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YOU KNOW, ABOUT
THE PHASE DIAGRAM OF WATER.

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IF YOU GO
FROM ONE FORM TO ANOTHER,

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YOU EXCHANGE ENERGY.

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YOU GIVE UP ENERGY,
YOU TAKE IN ENERGY

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TO MOVE
FROM ONE STATE TO ANOTHER.

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THE UNIQUE THING ABOUT WATER IS,
FOR EXAMPLE,

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IF YOU MAKE A SOLID,
THE SOLID FLOATS.

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CAN'T THINK OF ANYTHING ELSE
THAT HAS THOSE CONDITIONS.

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- AND WE KNOW HOW IMPORTANT
FLOATING ICE IS

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TO LIFE HERE ON EARTH.

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WATER ACTUALLY BECOMES
LESS DENSE AS IT FREEZES.

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HOW CAN THAT HAPPEN?

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AS WATER FREEZES,

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THE HYDROGEN BONDS
IN THE WATER MOLECULES

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FORM CRYSTALS,

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AND THE MOLECULES ACTUALLY
SPREAD OUT A BIT.

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AS A RESULT, A BLOCK OF ICE
IS LESS DENSE.

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IT IS LIGHTER IN WEIGHT THAN
THE SAME VOLUME OF LIQUID WATER.

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WITHOUT THIS UNIQUE PROPERTY
OF WATER,

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THE ICE THAT FORMS
ON THE TOP OF A POND OR LAKE

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WOULD SINK TO THE BOTTOM,

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AND THE ENTIRE LAKE
WOULD EVENTUALLY FREEZE.

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INSTEAD, ICE FORMS A LAYER
ON THE TOP OF THE LAKE

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THAT ACTUALLY SERVES
AS INSULATION

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TO PROTECT THE FISH AND OTHER
WATER ANIMALS FROM FREEZING.

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RIGHT, SO WHAT DOES ADDING
OR REMOVING ENERGY

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OR ICE FLOATING
HAVE TO DO WITH A SNOWBALL?

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WELL, FIRST, WE NEED TO LOOK
AT A PHASE DIAGRAM LIKE THIS.

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BASICALLY, WHAT A PHASE DIAGRAM
SHOWS YOU

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IS WHAT PHASE OF MATTER
A SUBSTANCE WOULD BE

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UNDER CERTAIN CONDITIONS
OF PRESSURE AND TEMPERATURE.

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- ANYTHING THAT HAS WATER IN IT,

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YOU CAN MORE OR LESS DESCRIBE
WITHIN THAT PHASE DIAGRAM.

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AS YOU MOVE FROM AN ICE
TO A WATER TO A VAPOR,

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YOU'RE EXCHANGING ENERGY
AND DRIVING--

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YOU HAVE TO EITHER LOSE ENERGY
OR GAIN ENERGY

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AS YOU MOVE BACK AND FORTH.

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- SO WHEN YOU ADD
OR REMOVE ENERGY,

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THAT LEADS TO CHANGES
IN TEMPERATURE.

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YOU PROBABLY KNOW THAT
WHEN YOU CHANGE TEMPERATURE,

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YOU CAN CHANGE
THE PHASE OF THE MATTER.

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HERE'S AN EASY EXAMPLE.

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WHEN YOU BOIL LIQUID WATER,
IT GETS HOT.

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AND ONCE IT REACHES
100 DEGREES CELSIUS,

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IT PHASE-CHANGES
TO A GAS, OR VAPOR.

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BUT YOU PROBABLY DIDN'T KNOW
THAT YOU CAN CHANGE

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A SUBSTANCE'S STATE OF MATTER

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BY CHANGING THE PRESSURE
EXERTED ON THE SUBSTANCE.

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AS PRESSURE INCREASES,

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THE MOLECULES IN A SUBSTANCE
ARE PUSHED CLOSER TOGETHER.

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AND IN MOST SUBSTANCES,

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WHEN THEY'RE SQUEEZED
HARD ENOUGH,

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THEY'RE COMPRESSED INTO SOLIDS.

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BUT NOT WATER.

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IN ITS LIQUID STATE,

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WATER MOLECULES
ARE ACTUALLY CLOSER TOGETHER

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THAN IN THE SOLID STATE.

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SO THAT MEANS,
YOU CAN APPLY PRESSURE TO ICE,

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AND IT WILL ACTUALLY
TURN TO LIQUID.

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YOU CAN CHECK THIS OUT
PRETTY EASILY.

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YOU JUST NEED
A PIECE OF STRING, ICE,

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AND TWO WEIGHTS
TO TIE TO THE STRING.

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AND, NO, YOU DON'T NEED SALT.

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IT ISN'T THAT KIND
OF DEMONSTRATION.

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JUST TIE THE WEIGHTS
TO THE ENDS OF THE STRING,

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HANG THE STRING ON THE ICE,
AND WAIT.

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YOU MIGHT HAVE TO WAIT
A LONG TIME,

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BUT EVENTUALLY,
THE PRESSURE OF THE STRING

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WILL CAUSE THE ICE TO CHANGE
PHASES INTO LIQUID,

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ALLOWING THE STRING
TO SLOWLY CUT THROUGH IT.

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NOW, BECAUSE THE REST OF THE ICE
IS STILL FROZEN,

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THE LIQUID WILL REFREEZE
OVER THE STRING.

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COOL, RIGHT?

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SO REALLY, HOW IS WATER
DIFFERENT FROM OTHER SUBSTANCES?

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TAKE A LOOK AT THIS.

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ON THE RIGHT IS THE PHASE
DIAGRAM FOR CARBON DIOXIDE,

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WHICH ACTS LIKE MOST SUBSTANCES.

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ON THE LEFT IS THE PHASE DIAGRAM
FOR WATER.

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LOOK AT THE LINES DIVIDING
THE LIQUID PHASES

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FROM THEIR RESPECTIVE
SOLID PHASES.

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IN THE WATER,
IF THE TEMPERATURE IS DECREASED

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BELOW ZERO DEGREES CELSIUS
BUT THE PRESSURE IS HIGH,

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LIKE IN THIS REGION,

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WATER CAN STILL BE
IN LIQUID STATE.

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BUT IN THE CARBON DIOXIDE,
LIKE MOST OTHER SUBSTANCES,

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INCREASED PRESSURE WILL
ACTUALLY MAKE IT MORE LIKELY

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FOR THE SUBSTANCE
TO BE IN A SOLID STATE.

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SOMETHING ELSE
TO TAKE INTO ACCOUNT:

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LIQUID WATER IS MORE DENSE
THAN SOLID WATER.

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THAT'S WHY ICE CUBES FLOAT.

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AND THAT ALSO PLAYS A KEY ROLL
IN MAKING A SNOWBALL.

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TO MAKE A SNOWBALL,
YOU HAVE TO COMPACT THE SNOW,

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WHICH TEMPORARILY
INCREASES THE PRESSURE.

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THIS CAUSES
SOME OF THE SNOW TO MELT.

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WHEN YOU STOP PRESSING,
THE WATER REFREEZES,

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AND THAT'S WHAT
HOLDS THE SNOWBALL TOGETHER.

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PRETTY SIMPLE:
WATER, PRESSURE, AND SNOWBALLS.

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OH, AND TEMPERATURE.

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DID I MENTION TEMPERATURE?

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IF IT'S MORE THAN A FEW DEGREES
BELOW FREEZING,

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YOU CANNOT SQUEEZE HARD ENOUGH

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TO CREATE ENOUGH PRESSURE
WITH YOUR HANDS

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TO CHANGE THE SNOW INTO A LIQUID
AND MAKE THAT SNOWBALL.

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IN FACT, AT THE SOUTH POLE,

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AT TEMPERATURES AROUND
NEGATIVE 25 DEGREES CELSIUS--

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THAT'S NEGATIVE 13 DEGREES
FAHRENHEIT,

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YOU'LL NEED ABOUT
THE SAME AMOUNT OF PRESSURE

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TO MAKE A SNOWBALL AS YOU WOULD
NEED TO CRUSH A SUBMARINE.

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NOW YOU KNOW WHY THERE AREN'T
ANY SNOWBALL BATTLES

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IN ANTARCTICA.

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EVEN THOUGH MARS
IS THE NEXT WARMEST PLACE

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IN THE SOLAR SYSTEM,

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WITH ENOUGH WATER ICE
TO THINK ABOUT SNOWBALLS,

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THERE'S NO WAY
YOU CAN MAKE SNOWBALLS THERE.

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DURING WINTER,
A LOW TEMPERATURE AT THE POLE

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IS ABOUT
NEGATIVE 125 DEGREES CELSIUS,

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OR NEGATIVE 195 DEGREES
FAHRENHEIT.

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THE AVERAGE TEMPERATURE ON MARS

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IS ABOUT NEGATIVE
60 DEGREES CELSIUS.

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THAT'S NEGATIVE 80 DEGREES
FAHRENHEIT.

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NO MARTIAN SNOWBALL BATTLES.

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SORRY.

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AND YOU JUST CAN'T MAKE
SNOWBALLS ON MARS

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OR THE MOON
OR ANY OTHER PLACE,

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AT LEAST THAT WE KNOW OF
RIGHT NOW.

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BESIDES, NASA'S GOT
MORE IMPORTANT GOALS

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FOR THE USE OF WATER ICE
ON OTHER HEAVENLY BODIES.

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FOR EXAMPLE:
IN-SITU RESOURCE UTILIZATION,

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USING MATERIALS
FOUND WHERE YOU'RE GOING

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RATHER THAN BRINGING
EVERYTHING WITH YOU.

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AND, HEY,
MAYBE THE KEPLER MISSION

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WILL FIND ANOTHER PLANET WHERE
IT'S POSSIBLE TO MAKE SNOWBALLS

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AND MY DREAMS
OF AN OTHER-WORLDLY SNOWBALL

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WON'T JUST HAVE
A SNOWBALL'S CHANCE IN...MARS.

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THAT'S IT FOR NOW.

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I'M AUDREY STAPLES SIGNING OFF
FOR "NASA LAUNCHPAD."

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THANKS FOR WATCHING.