The Edge of the Solar System

(SFX:wind in trees or storm)

     THE EARTH'S WIND CAN SPEED UP TO 300 MILES AN HOUR DURING A HEAVY
TORNADO,  BUT THAT'S NOTHING COMPARED TO SOLAR WINDS WHICH STREAM OUT
FROM THE SUN AT CLOSER TO A MILLION MILES AN HOUR.  LUCKILY, SOLAR WINDS ARE
MADE OF SUCH TINY PARTICLES THAT WE DON'T FEEL THEM AS THEY WHIP PAST THE
EARTH OUT INTO THE FARTHEST REACHES OF THE SOLAR SYSTEM. BUT JUST BECAUSE
THEY DON'T INTERACT WITH PEOPLE DOESN'T MEAN THEY AREN'T INTERESTING. THEY
SPEED OUT PAST PLUTO AND EVENTUALLY COME IN CONTACT WITH THE
INTERSTELLAR MEDIUM--THAT'S THE STUFF THAT'S STREAMING FROM ALL THE OTHER
STARS IN THE GALAXY. THAT BORDER IS CALLED THE HELIOPAUSE, AND IT MARKS THE
VERY EDGE OF OUR SOLAR SYSTEM, SAYS PHYSICIST JOHN BELCHER AT MIT.  HE'S
STUDYING THE OUTER REACHES OF THE SOLAR SYSTEM THROUGH 2 NASA
SPACECRAFT, VOYAGER 1 AND 2, THAT WERE LAUNCHED 15 YEARS AGO AND ARE STILL
HEADING STEADILY TOWARDS THE HELIOPAUSE. 

     Belcher: "There are very few particles up there, but they are very interesting. the disk of the galaxy
is full of these." 
     THE VOYAGER SPACECRAFT SEND BACK INFORMATION ABOUT THEIR
SURROUNDINGS AND BELCHER HAS FOUND THAT THE EDGE OF THE SOLAR SYSTEM IS
NOT JUST A BORING VACUUM.  TRUE THERE ARE ONLY A FEW PROTONS FOR EVERY
CUBIC FOOT WHICH IS MUCH STRONGER THAN THE  VACUUM NEEDED TO POWER YOUR
AVERAGE HOOVER VACUUM CLEANER, BUT THOSE PROTONS COME IN BURSTS,
FORMING CHANGING CURRENTS AND EDDIES.

     BELCHER: "There's a lot more strucutre out there than we expected to see.  I think the general
picture was that. . . Everything would be a smooth featureless flow and it's anything but." 

     THAT FLOW IS ESPECIALLY INTERESTING RIGHT AT THE HELIOPAUSE.  OUR
ENTIRE SOLAR SYSTEM SITS LIKE A ROCK IN A RIVER, AS THE INTERSTELLAR WINDS
CIRCLE AROUND IT. JUST WHAT THAT BORDER LOOKS LIKE WILL BE ONE OF THE
THINGS THE TWO VOYAGERS WILL EXAMINE, AS THEY CROSS THAT BORDER SOME
TIME WITHIN THE NEXT 20 YEARS.  ONCE ACROSS THE HELIOPAUSE, THEY WILL BE THE
VERY FIRST MANMADE OBJECTS TO LEAVE OUR SOLAR SYSTEM.