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http://www.jpl.nasa.gov/news/news.cfm?release=2011-128  

Voyager Set to Enter Interstellar Space
Jet Propulsion Laboratory
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 the California Institute of Technology
in Pasadena, 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 interstellar space in our Milky Way
galaxy.

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,"
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.

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.

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 the spacecraft 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."

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.

The Voyagers were built by NASA's Jet Propulsion Laboratory in Pasadena,
Calif., which continues to operate both spacecraft. JPL is a division of
the California Institute of Technology in Pasadena. The Voyager missions
are a part of the NASA Heliophysics System Observatory, sponsored by the
Heliophysics Division of the Science Mission Directorate.

For more information about the Voyager spacecraft, visit:

http://voyager.jpl.nasa.gov and http://www.nasa.gov/voyager .

Written by Tony Phillips
Contact:
Jia-Rui Cook 818-354-0850/359-3241
Jet Propulsion Laboratory, Pasadena, Calif.
jccook{at}jpl.nasa.gov

2011-128

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