WEBVTT

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- DAYS THAT CONSIST
OF 24 HOURS

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AND YEARS
MEASURED BY 365 DAYS

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ARE PRETTY STANDARD UNITS
OF TIME FOR US HERE ON EARTH.

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BUT ON THE PLANET
CLOSEST TO THE SUN,

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TIME TAKES ON
A WHOLE NEW MEANING.

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JUST HOW CAN THAT BE?

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FIND OUT NEXT
ON "REAL WORLD."

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THE SUN'S PULL ON MERCURY
HAS ACTUALLY SLOWED DOWN

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THE ROTATION
OF THIS SMALL PLANET.

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AS A RESULT, ONE FULL DAY--
THAT'S NOON TO NOON--

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TAKES ABOUT 176 EARTH-DAYS.

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A DAY ON MERCURY
WOULD LAST 4,2224 HOURS.

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THAT'S A LONG TIME
TO BE IN SCHOOL.

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SO WHAT ELSE DO WE KNOW
ABOUT MERCURY?

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IT'S THE CLOSEST PLANET
TO OUR SUN,

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AND LIKE EARTH,
IT'S TERRESTRIAL.

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ITS TEMPERATURE RANGES

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FROM A SCORCHING
427 DEGREES CELSIUS

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WHEN THE SUN SHINES
ON THE SURFACE

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TO A FRIGID
NEGATIVE 173 DEGREES CELSIUS

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ON ITS NIGHT SIDE.

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IN MANY WAYS,
THE SURFACE OF MERCURY

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IS MUCH LIKE THAT OF OUR MOON:
HEAVILY CRATERED AND OLD.

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BUT FOR EVERYTHING WE KNOW
ABOUT MERCURY,

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WE HAVE EVEN MORE QUESTIONS.

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LET'S TALK TO PETER BEDINI

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FROM THE JOHNS HOPKINS
APPLIED PHYSICS LABORATORY

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TO FIND OUT WHAT MAKES MERCURY
SO MYSTERIOUS.

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– THERE ARE SEVERAL THINGS

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THAT CONFUSE US
ABOUT THE PLANET.

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IT IS VERY DENSE
TO BEGIN WITH.

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WE DON'T KNOW WHY.

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IT DOESN'T HAVE AN ATMOSPHERE.

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THERE ARE SO FEW PARTICLES
IN THE ENVIRONMENT

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THAT THEY CALL IT AN EXOSPHERE,

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AND IT'S TENUOUS.

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IT'S WISPY.

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IT SORT OF MOVES A LOT.

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IT'S VERY DYNAMIC.

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MERCURY HAS A DYNAMIC
MAGNETIC FIELD,

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LIKE EARTH, BUT SMALLER,

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AND THAT'S VERY UNUSUAL
FOR A PLANET OF THAT AGE.

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YOU'D THINK THAT
THAT MAGNETIC FIELD

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WOULD BE GONE ALREADY.

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IT ALSO HAS SIGNS ON IT

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THAT THERE WAS VOLCANISM
ON THE PLANET.

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SO THERE ARE A LOT OF MYSTERIES
ABOUT THE PLANET.

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- MERCURY'S POSITION
SO CLOSE TO THE SUN

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MAKES IT DIFFICULT TO STUDY.

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NOT EVEN HUBBLE, OUR MOST
POWERFUL SPACE TELESCOPE,

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CAN LOOK AT MERCURY WITHOUT
PERMANENTLY DAMAGING ITS OPTICS.

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SO HOW CAN WE LEARN MORE
ABOUT THIS UNUSUAL PLANET?

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ONLY ONE NASA SPACECRAFT,
MARINER 10,

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HAS EVER VISITED
THE PLANET MERCURY.

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MARINER 10 WAS PROGRAMMED
TO FLY BY MERCURY THREE TIMES

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AND TAKE IMAGES
OF THE HEAVILY CRATERED SURFACE.

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UNFORTUNATELY,
THE SPACECRAFT ESSENTIALLY SAW

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THE SAME SIDE OF THE PLANET
ON EACH FLYBY.

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SCIENTISTS AND ENGINEERS
SPENT THE NEXT DECADES

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DEVELOPING NEW TECHNIQUES
AND DESIGNING A SPACECRAFT

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THAT COULD SURVIVE THE EXTREME
CONDITIONS OF MERCURY.

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NASA'S MESSENGER MISSION
IS THE RESULT OF THEIR WORK.

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MESSENGER--
OR THE MERCURY SURFACE,

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SPACE ENVIRONMENT,
GEOCHEMISTRY, AND RANGING--

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IS THE FIRST MISSION TO MERCURY
IN OVER 30 YEARS.

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MESSENGER COMPLETED
THREE FLYBYS OF MERCURY,

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CAPTURING STUNNING
NEVER-BEFORE-SEEN IMAGERY

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OF THE SURFACE

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BEFORE EVENTUALLY
INSERTING ITSELF

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INTO ORBIT AROUND THE PLANET.

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A NEAT NAVIGATIONAL TECHNIQUE

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THAT MESSENGER USED
ON THE WAY TO MERCURY

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WAS THE USE
OF SOLAR RADIATION PRESSURE,

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OR SOLAR SAILING,
TO GUIDE THE PROBE'S TRAJECTORY.

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- WE REALIZED THAT BY CHANGING
THE ANGLES OF OUR SOLAR PANELS

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OR TILTING THE BODY

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AND EXPOSING DIFFERENT SURFACES
TO THE SUN,

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WE COULD ACTUALLY AFFECT
WHAT PATH THE SPACECRAFT TAKES,

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AND WE CAN TWEAK THE TRAJECTORY
A LITTLE BIT.

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THE BIGGEST SAVINGS
THAT GIVES YOU

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IS THAT YOU DON'T
GO THROUGH THE RISK

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OF OPERATING YOUR THRUSTERS.

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WHENEVER YOU DO THAT,

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IT'S ALWAYS RISKY
TO THE SPACECRAFT.

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SO BY USING SOLAR SAILING

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AND JUST SAILING
ON THE SOLAR PRESSURE

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LIKE A SAILBOAT DOES
IN THE WIND,

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WE WERE ABLE
TO DIRECT THE SPACECRAFT

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WHERE WE WANTED IT TO BE.

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- AND NOW THAT MESSENGER
IS IN ORBIT,

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THE SPACECRAFT WILL ALLOW US
TO OBSERVE MERCURY

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AS IT HAS NEVER
BEEN SEEN BEFORE.

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– WE'LL BE ABLE TO CHARACTERIZE
ALL ASPECTS OF THE PLANET,

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FROM THE INNER CORE

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TO FIND OUT IF IT'S ACTUALLY
LIQUID OR SOLID

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AND IF IT'S DYNAMIC--

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MAYBE THAT'S THE SOURCE
OF THE MAGNETIC FIELD--

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TO THE COMPOSITION
OF THE SURFACE

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BY USING A CAMERA SYSTEM
THAT TAKES PICTURES

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IN 11 DIFFERENT COLORS.

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AND BY LOOKING
AT THE DIFFERENT COLORS,

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YOU CAN TELL THE COMPOSITION
OF THE SURFACE.

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WE HAVE A GAMMA RAY
NEUTRON SPECTROMETER,

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OR X-RAY SPECTROMETER,

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THAT CAN TELL
THE DIFFERENT ELEMENTS

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THAT MAKE UP THE SURFACE.

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AND WE HAVE A MAGNETOMETER,
OF COURSE,

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TO MEASURE THE MAGNETIC FIELD
AND CHARACTERIZE IT.

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- BUT WHY BOTHER
STUDYING MERCURY?

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HOW WILL KNOWING MORE
ABOUT THIS PLANET

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AFFECT US HERE ON EARTH?

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A FAMILY PORTRAIT,

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ONE OF MESSENGER'S
NEWEST CONTRIBUTIONS,

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HELPS US ANSWER THAT QUESTION.

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THE 34-IMAGE MOSAIC
OF THE SOLAR SYSTEM

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GIVES SCIENTISTS A SNAPSHOT
OF NEIGHBORING PLANETS

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FROM MERCURY'S PERSPECTIVE.

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THESE IMAGES
HELP US UNDERSTAND THAT EARTH

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IS A PART OF A PLANETARY FAMILY
FORMED BY COMMON PROCESSES.

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- THE WAY I THINK OF IT
IS THAT THE SOLAR SYSTEM

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IS LIKE A LARGE LABORATORY,

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AND IT HAS IN IT
A LOT OF PLANETARY BODIES

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VERY SIMILAR TO EARTH.

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MERCURY IS JUST ONE

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THAT'S ONE
OF THE MORE ELUSIVE ONES

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THAT WE'RE NOW GOING
TO FILL IN THAT GAP.

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IT'S SORT OF AN EXTREME CASE
OF THE TERRESTRIAL PLANETS.

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IT'S CLOSEST TO THE SUN.

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IT HAS THESE FEATURES
I MENTIONED

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LIKE THE MAGNETIC FIELD
AND HIGH DENSITY.

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AND BY LEARNING HOW IT EVOLVED

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AND KNOWING WHAT WE KNOW ABOUT
THE OTHER TERRESTRIAL PLANETS,

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WE CAN LEARN A LOT MORE

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ABOUT HOW EARTH ITSELF EVOLVED,
HOW IT CAME TO BE.

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- BY GATHERING DATA
ABOUT MERCURY,

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WE'LL BE ABLE TO GAIN
SOME INSIGHT

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INTO OUR OWN HISTORY.

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AND WITH THE MESSENGER
SPACECRAFT

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HELPING US UNVEIL
MERCURY'S MYSTERIES,

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WHO KNOWS WHAT ASTRONOMERS
WILL FIGURE OUT

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BEFORE THE NEXT DAY
ON MERCURY GOES BY?

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SEE YOU NEXT TIME
ON "REAL WORLD."