Voyager Set to Enter the Milky Way - presented by Science@NASA
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 JPL, Voyager Project Scientist since 1972.
"Voyager 1 and 2 seem to have a knack for making discoveries."
On April,28, 2011, NASA held a press conference 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. The Voyager-adventure began in the
late 1970's and 80's when the probes took a Grand Tour of the outer planets.
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
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.
There was the discovery of volcanoes on Jupiter's moon Io, evidence for an
underground ocean on Europa, hints of methane rain on Saturn's moon Titan, the
crazily-tipped magnetic poles of Uranus and Neptune, 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," says
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. Sailing into the void sounds
like a quiet time, but the discoveries have continued. Voyager 1 and 2 are now
at the edge of the solar system, in a place called the "heliosheath," where the
solar wind meets interstellar gas for the first time.
This 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.
Soon, in a matter of years, the two probes will leave the solar system
altogether and enter the realm of the stars, interstellar space, the Milky Way
itself. Then they will have a new job: Ambassador. Each probe is famously
equipped with a Golden Record, literally, a gold-coated copper phonograph
record. It contains more than 100 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 60 human languages and one whale language; and the brain waves of a
young woman in love.
A team led by Carl Sagan assembled the record as a message to possible
extraterrestrial civilizations that might encounter the spacecraft. Some people
say 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
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?