[rocket rumbling]
[percussive music]
- HEY, WELCOME TO "NASA LAUNCHPAD."
I'M YOUR HOST, AUDREY STAPLES.
SO WHAT'S ONE OF THE MAIN REASONS THAT NASA RESEARCHERS
ARE SO EXCITED THESE DAYS?
WELL, WE'RE TALKING ABOUT WATER.
SURE, WATER'S A BIG PART OF LIFE HERE ON EARTH,
A HUGE PART, ACTUALLY.
BUT IT'S NOT AS COMMON ON OTHER BODIES
THROUGHOUT OUR SOLAR SYSTEM.
SO WHETHER WE'RE TALKING ABOUT THE WATER ICE
THAT THE MARS PHOENIX LANDER DISCOVERED
OR, MORE RECENTLY, THE WATER ICE
KICKED UP BY LCROSS ON THE MOON,
NOW'S A GOOD TIME TO START THINKING
ABOUT WHAT WE CAN USE THAT WATER ICE FOR.
WHAT WOULD I DO WITH IT?
START PACKING IT UP
AND FLINGING SOME MARTIAN AND LUNAR SNOWBALLS.
BUT I'VE BEEN TOLD, I CAN'T MAKE A SNOWBALL ON MARS
OR ON THE MOON, FOR THAT MATTER,
OR ANYWHERE ELSE WE KNOW OF EXCEPT EARTH.
BUT WHY NOT?
WELL, LET'S IGNORE THE FACT THAT I'M NOT AN ASTRONAUT,
SO I WON'T BE LEAVING EARTH ANYTIME SOON.
THERE ARE TWO MAIN REASONS
WHY SNOWBALLS CAN ONLY BE MADE ON EARTH:
SO LET'S EXPLORE THESE REASONS A BIT FURTHER.
AND FOR THAT, LET'S TALK TO DR. PETER WASILEWSKI
OF NASA GODDARD SPACE FLIGHT CENTER.
- LIFE ON EARTH AND ALL ITS SEASONS IS,
YOU KNOW, ABOUT THE PHASE DIAGRAM OF WATER.
IF YOU GO FROM ONE FORM TO ANOTHER,
YOU EXCHANGE ENERGY.
YOU GIVE UP ENERGY, YOU TAKE IN ENERGY
TO MOVE FROM ONE STATE TO ANOTHER.
THE UNIQUE THING ABOUT WATER IS, FOR EXAMPLE,
IF YOU MAKE A SOLID, THE SOLID FLOATS.
CAN'T THINK OF ANYTHING ELSE THAT HAS THOSE CONDITIONS.
- AND WE KNOW HOW IMPORTANT FLOATING ICE IS
TO LIFE HERE ON EARTH.
WATER ACTUALLY BECOMES LESS DENSE AS IT FREEZES.
HOW CAN THAT HAPPEN?
AS WATER FREEZES,
THE HYDROGEN BONDS IN THE WATER MOLECULES
FORM CRYSTALS,
AND THE MOLECULES ACTUALLY SPREAD OUT A BIT.
AS A RESULT, A BLOCK OF ICE IS LESS DENSE.
IT IS LIGHTER IN WEIGHT THAN THE SAME VOLUME OF LIQUID WATER.
WITHOUT THIS UNIQUE PROPERTY OF WATER,
THE ICE THAT FORMS ON THE TOP OF A POND OR LAKE
WOULD SINK TO THE BOTTOM,
AND THE ENTIRE LAKE WOULD EVENTUALLY FREEZE.
INSTEAD, ICE FORMS A LAYER ON THE TOP OF THE LAKE
THAT ACTUALLY SERVES AS INSULATION
TO PROTECT THE FISH AND OTHER WATER ANIMALS FROM FREEZING.
RIGHT, SO WHAT DOES ADDING OR REMOVING ENERGY
OR ICE FLOATING HAVE TO DO WITH A SNOWBALL?
WELL, FIRST, WE NEED TO LOOK AT A PHASE DIAGRAM LIKE THIS.
BASICALLY, WHAT A PHASE DIAGRAM SHOWS YOU
IS WHAT PHASE OF MATTER A SUBSTANCE WOULD BE
UNDER CERTAIN CONDITIONS OF PRESSURE AND TEMPERATURE.
- ANYTHING THAT HAS WATER IN IT,
YOU CAN MORE OR LESS DESCRIBE WITHIN THAT PHASE DIAGRAM.
AS YOU MOVE FROM AN ICE TO A WATER TO A VAPOR,
YOU'RE EXCHANGING ENERGY AND DRIVING--
YOU HAVE TO EITHER LOSE ENERGY OR GAIN ENERGY
AS YOU MOVE BACK AND FORTH.
- SO WHEN YOU ADD OR REMOVE ENERGY,
THAT LEADS TO CHANGES IN TEMPERATURE.
YOU PROBABLY KNOW THAT WHEN YOU CHANGE TEMPERATURE,
YOU CAN CHANGE THE PHASE OF THE MATTER.
HERE'S AN EASY EXAMPLE.
WHEN YOU BOIL LIQUID WATER, IT GETS HOT.
AND ONCE IT REACHES 100 DEGREES CELSIUS,
IT PHASE-CHANGES TO A GAS, OR VAPOR.
BUT YOU PROBABLY DIDN'T KNOW THAT YOU CAN CHANGE
A SUBSTANCE'S STATE OF MATTER
BY CHANGING THE PRESSURE EXERTED ON THE SUBSTANCE.
AS PRESSURE INCREASES,
THE MOLECULES IN A SUBSTANCE ARE PUSHED CLOSER TOGETHER.
AND IN MOST SUBSTANCES,
WHEN THEY'RE SQUEEZED HARD ENOUGH,
THEY'RE COMPRESSED INTO SOLIDS.
BUT NOT WATER.
IN ITS LIQUID STATE,
WATER MOLECULES ARE ACTUALLY CLOSER TOGETHER
THAN IN THE SOLID STATE.
SO THAT MEANS, YOU CAN APPLY PRESSURE TO ICE,
AND IT WILL ACTUALLY TURN TO LIQUID.
YOU CAN CHECK THIS OUT PRETTY EASILY.
YOU JUST NEED A PIECE OF STRING, ICE,
AND TWO WEIGHTS TO TIE TO THE STRING.
AND, NO, YOU DON'T NEED SALT.
IT ISN'T THAT KIND OF DEMONSTRATION.
JUST TIE THE WEIGHTS TO THE ENDS OF THE STRING,
HANG THE STRING ON THE ICE, AND WAIT.
YOU MIGHT HAVE TO WAIT A LONG TIME,
BUT EVENTUALLY, THE PRESSURE OF THE STRING
WILL CAUSE THE ICE TO CHANGE PHASES INTO LIQUID,
ALLOWING THE STRING TO SLOWLY CUT THROUGH IT.
NOW, BECAUSE THE REST OF THE ICE IS STILL FROZEN,
THE LIQUID WILL REFREEZE OVER THE STRING.
COOL, RIGHT?
SO REALLY, HOW IS WATER DIFFERENT FROM OTHER SUBSTANCES?
TAKE A LOOK AT THIS.
ON THE RIGHT IS THE PHASE DIAGRAM FOR CARBON DIOXIDE,
WHICH ACTS LIKE MOST SUBSTANCES.
ON THE LEFT IS THE PHASE DIAGRAM FOR WATER.
LOOK AT THE LINES DIVIDING THE LIQUID PHASES
FROM THEIR RESPECTIVE SOLID PHASES.
IN THE WATER, IF THE TEMPERATURE IS DECREASED
BELOW ZERO DEGREES CELSIUS BUT THE PRESSURE IS HIGH,
LIKE IN THIS REGION,
WATER CAN STILL BE IN LIQUID STATE.
BUT IN THE CARBON DIOXIDE, LIKE MOST OTHER SUBSTANCES,
INCREASED PRESSURE WILL ACTUALLY MAKE IT MORE LIKELY
FOR THE SUBSTANCE TO BE IN A SOLID STATE.
SOMETHING ELSE TO TAKE INTO ACCOUNT:
LIQUID WATER IS MORE DENSE THAN SOLID WATER.
THAT'S WHY ICE CUBES FLOAT.
AND THAT ALSO PLAYS A KEY ROLL IN MAKING A SNOWBALL.
TO MAKE A SNOWBALL, YOU HAVE TO COMPACT THE SNOW,
WHICH TEMPORARILY INCREASES THE PRESSURE.
THIS CAUSES SOME OF THE SNOW TO MELT.
WHEN YOU STOP PRESSING, THE WATER REFREEZES,
AND THAT'S WHAT HOLDS THE SNOWBALL TOGETHER.
PRETTY SIMPLE: WATER, PRESSURE, AND SNOWBALLS.
OH, AND TEMPERATURE.
DID I MENTION TEMPERATURE?
IF IT'S MORE THAN A FEW DEGREES BELOW FREEZING,
YOU CANNOT SQUEEZE HARD ENOUGH
TO CREATE ENOUGH PRESSURE WITH YOUR HANDS
TO CHANGE THE SNOW INTO A LIQUID AND MAKE THAT SNOWBALL.
IN FACT, AT THE SOUTH POLE,
AT TEMPERATURES AROUND NEGATIVE 25 DEGREES CELSIUS--
THAT'S NEGATIVE 13 DEGREES FAHRENHEIT,
YOU'LL NEED ABOUT THE SAME AMOUNT OF PRESSURE
TO MAKE A SNOWBALL AS YOU WOULD NEED TO CRUSH A SUBMARINE.
NOW YOU KNOW WHY THERE AREN'T ANY SNOWBALL BATTLES
IN ANTARCTICA.
EVEN THOUGH MARS IS THE NEXT WARMEST PLACE
IN THE SOLAR SYSTEM,
WITH ENOUGH WATER ICE TO THINK ABOUT SNOWBALLS,
THERE'S NO WAY YOU CAN MAKE SNOWBALLS THERE.
DURING WINTER, A LOW TEMPERATURE AT THE POLE
IS ABOUT NEGATIVE 125 DEGREES CELSIUS,
OR NEGATIVE 195 DEGREES FAHRENHEIT.
THE AVERAGE TEMPERATURE ON MARS
IS ABOUT NEGATIVE 60 DEGREES CELSIUS.
THAT'S NEGATIVE 80 DEGREES FAHRENHEIT.
NO MARTIAN SNOWBALL BATTLES.
SORRY.
AND YOU JUST CAN'T MAKE SNOWBALLS ON MARS
OR THE MOON OR ANY OTHER PLACE,
AT LEAST THAT WE KNOW OF RIGHT NOW.
BESIDES, NASA'S GOT MORE IMPORTANT GOALS
FOR THE USE OF WATER ICE ON OTHER HEAVENLY BODIES.
FOR EXAMPLE: IN-SITU RESOURCE UTILIZATION,
USING MATERIALS FOUND WHERE YOU'RE GOING
RATHER THAN BRINGING EVERYTHING WITH YOU.
AND, HEY, MAYBE THE KEPLER MISSION
WILL FIND ANOTHER PLANET WHERE IT'S POSSIBLE TO MAKE SNOWBALLS
AND MY DREAMS OF AN OTHER-WORLDLY SNOWBALL
WON'T JUST HAVE A SNOWBALL'S CHANCE IN...MARS.
THAT'S IT FOR NOW.
I'M AUDREY STAPLES SIGNING OFF FOR "NASA LAUNCHPAD."
THANKS FOR WATCHING.