Voyager Set to Enter Interstellar Space   
       
   April 28, 2011: More than 30 years after they left Earth, NASA's twin Voyager   
   probes are now at the edge of the solar system. Not only that, they're still   
   working. And with each passing day they are beaming back a message that, to   
   scientists, is both unsettling and thrilling.   
       
   The message is, "Expect the unexpected."   
       
   "It's uncanny," says Ed Stone of Caltech, Voyager Project Scientist since   
   1972. "Voyager 1 and 2 have a knack for making discoveries."   
       
   Today, April 28, 2011, NASA held a live briefing to reflect on what the   
   Voyager mission has accomplished--and to preview what lies ahead as the probes   
   prepare to enter the realm of the Milky Way itself.   
   [...]   
   Click to view a video about Voyager's incredible journey to the edge of the   
   solar system.   
       
   The adventure began in the late 1970s when the probes took advantage of a rare   
   alignment of outer planets for an unprecedented Grand Tour. Voyager 1 visited   
   Jupiter and Saturn, while Voyager 2 flew past Jupiter, Saturn, Uranus and   
   Neptune. (Voyager 2 is still the only probe to visit Uranus and Neptune.) [...]   
   When pressed to name the top discoveries from those encounters, Stone pauses,   
   not for lack of material, but rather an embarrassment of riches. "It's so hard   
   to choose," he says.   
       
   Stone's partial list includes the discovery of volcanoes on Jupiter's moon Io;   
   evidence for an ocean beneath the icy surface of Europa; hints of methane rain   
   on Saturn's moon Titan; the crazily-tipped magnetic poles of Uranus and   
   Neptune; icy geysers on Neptune's moon Triton; planetary winds that blow   
   faster and faster with increasing distance from the sun.   
       
   "Each of these discoveries changed the way we thought of other worlds," he   
   says Stone.   
       
   In 1980, Voyager 1 used the gravity of Saturn to fling itself slingshot-style   
   out of the plane of the Solar System. In 1989, Voyager 2 got a similar assist   
   from Neptune. Both probes set sail into the void.   
   [...]   
   The heliosphere in your kitchen sink. [video] Sailing into the void sounds   
   like a quiet time, but the discoveries have continued.   
       
   Stone sets the stage by directing our attention to the kitchen sink. "Turn on   
   the faucet," he instructs. "Where the water hits the sink, that's the sun, and   
   the thin sheet of water flowing radially away from that point is the solar   
   wind. Note how the sun 'blows a bubble' around itself."   
       
   There really is such a bubble, researchers call it the "heliosphere," and it   
   is gargantuan. Made of solar plasma and magnetic fields, the heliosphere is   
   about three times wider than the orbit of Pluto. Every planet, asteroid,   
   spacecraft, and life form belonging to our solar system lies inside.   
       
   The Voyagers are trying to get out, but they're not there yet. To locate them,   
   Stone peers back into the sink: "As the water (or solar wind) expands, it gets   
   thinner and thinner, and it can't push as hard. Abruptly, a sluggish,   
   turbulent ring forms. That outer ring is the heliosheath--and that is where   
   the Voyagers are now."   
       
   The heliosheath is a very strange place, filled with a magnetic froth no   
   spacecraft has ever encountered before, echoing with low-frequency radio   
   bursts heard only in the outer reaches of the solar system, so far from home   
   that the sun is a mere pinprick of light.   
       
   "In many ways, the heliosheath is not like our models predicted," says Stone.   
   [...]   
   Voyagers in the heliosheath. [more]   
       
   In June 2010 Voyager 1 beamed back a startling number: zero. That's the   
   outward velocity of the solar wind where the probe is now. No one thinks the   
   solar wind has completely stopped; it may have just turned a corner. But which   
   way? Voyager 1 is trying to figure that out through a series of "weather vane"   
   maneuvers, in which V1 turns itself in a different direction to track the   
   local breeze. The old spacecraft still has some moves left, it seems.   
       
   No one knows exactly how many more miles the Voyagers must travel before they   
   "pop free" into interstellar space. Most researchers believe, however, that   
   the end is near. "The heliosheath is 3 to 4 billion miles in thickness,"   
   estimates Stone. "That means we'll be out within five years or so."   
       
   There is plenty of power for the rest of the journey. Both Voyagers are   
   energized by the radioactive decay of a Plutonium 238 heat source. This should   
   keep critical subsystems running through at least 2020.   
       
   After that, he says, "Voyager will become our silent ambassador to the stars."   
   [...]   
   Voyager's golden record cover. [more]   
       
   Each probe is famously equipped with a Golden Record, literally, a gold-coated   
   copper phonograph record. It contains 118 photographs of Earth; 90 minutes of   
   the world's greatest music; an audio essay entitled Sounds of Earth (featuring   
   everything from burbling mud pots to barking dogs to a roaring Saturn 5   
   liftoff); greetings in 55 human languages and one whale language; the brain   
   waves of a young woman in love; and salutations from the Secretary General of   
   the United Nations. A team led by Carl Sagan assembled the record as a message   
   to possible extraterrestrial civilizations that might encounter the spacecraft.   
       
   "A billion years from now, when everything on Earth we've ever made has   
   crumbled into dust, when the continents have changed beyond recognition and   
   our species is unimaginably altered or extinct, the Voyager record will speak   
   for us," wrote Carl Sagan and Ann Druyan in an introduction to a CD version of   
   the record.   
       
   Some people note that the chance of aliens finding the Golden Record is   
   fantastically remote. The Voyager probes won't come within a few light years   
   of another star for some 40,000 years. What are the odds of making contact   
   under such circumstances?   
       
   On the other hand, what are the odds of a race of primates evolving to   
   sentience, developing spaceflight, and sending the sound of barking dogs into   
   the cosmos?   
       
   Expect the unexpected, indeed.   
       
       
   Author: Dr. Tony Phillips | Credit: Science@NASA   
       
   More Information   
   Voyager Interstellar Mission -- home page   
       
   Voyager videos and images   
       
       
   Regards,   
       
   Roger   
      
   --- D'Bridge 3.6   
    * Origin: NCS BBS (1:3828/7)