MEDIA RELATIONS OFFICE
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Written by Tony Phillips
Contact:
Jia-Rui Cook 818-354-0850/359-3241
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov
Feature: 2011-128 April 28, 2011
Voyager Set to Enter Interstellar Space
The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-128&cid=release_2011-128
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 .
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