NASA's Voyager Hits New Region at Solar System Edge

MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE 818-354-5011

Jia-Rui C. Cook/Alan Buis 818-354-0850/818-653-8339
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov/alan.d.buis@jpl.nasa.gov

Steve Cole 202-358-0918
NASA Headquarters, Washington
stephen.e.cole@nasa.gov

News release: 2011-372 Dec. 5, 2011

NASA's Voyager Hits New Region at Solar System Edge

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-372&cid=release_2011-372

PASADENA, Calif. -- NASA's Voyager 1 spacecraft has entered a new region between our solar
system and interstellar space. Data obtained from Voyager over the last year reveal this new region to
be a kind of cosmic purgatory. In it, the wind of charged particles streaming out from our sun has
calmed, our solar system's magnetic field is piled up, and higher-energy particles from inside our
solar system appear to be leaking out into interstellar space.

"Voyager tells us now that we're in a stagnation region in the outermost layer of the bubble around
our solar system," said Ed Stone, Voyager project scientist at the California Institute of Technology
in Pasadena. "Voyager is showing that what is outside is pushing back. We shouldn't have long to
wait to find out what the space between stars is really like."

Although Voyager 1 is about 11 billion miles (18 billion kilometers) from the sun, it is not yet in
interstellar space. In the latest data, the direction of the magnetic field lines has not changed,
indicating Voyager is still within the heliosphere, the bubble of charged particles the sun blows
around itself. The data do not reveal exactly when Voyager 1 will make it past the edge of the solar
atmosphere into interstellar space, but suggest it will be in a few months to a few years.

The latest findings, described today at the American Geophysical Union's fall meeting in San
Francisco, come from Voyager's Low Energy Charged Particle instrument, Cosmic Ray Subsystem
and Magnetometer.

Scientists previously reported the outward speed of the solar wind had diminished to zero in April
2010, marking the start of the new region. Mission managers rolled the spacecraft several times this
spring and summer to help scientists discern whether the solar wind was blowing strongly in another
direction. It was not. Voyager 1 is plying the celestial seas in a region similar to Earth's doldrums,
where there is very little wind.

During this past year, Voyager's magnetometer also detected a doubling in the intensity of the
magnetic field in the stagnation region. Like cars piling up at a clogged freeway off-ramp, the
increased intensity of the magnetic field shows that inward pressure from interstellar space is
compacting it.

Voyager has been measuring energetic particles that originate from inside and outside our solar
system. Until mid-2010, the intensity of particles originating from inside our solar system had been
holding steady. But during the past year, the intensity of these energetic particles has been declining,
as though they are leaking out into interstellar space. The particles are now half as abundant as they
were during the previous five years.

At the same time, Voyager has detected a 100-fold increase in the intensity of high-energy electrons
from elsewhere in the galaxy diffusing into our solar system from outside, which is another indication
of the approaching boundary.

"We've been using the flow of energetic charged particles at Voyager 1 as a kind of wind sock to
estimate the solar wind velocity," said Rob Decker, a Voyager Low-Energy Charged Particle
Instrument co-investigator at the Johns Hopkins University Applied Physics Laboratory in Laurel,
Md. "We've found that the wind speeds are low in this region and gust erratically. For the first time,
the wind even blows back at us. We are evidently traveling in completely new territory. Scientists
had suggested previously that there might be a stagnation layer, but we weren't sure it existed until
now."

Launched in 1977, Voyager 1 and 2 are in good health. Voyager 2 is 9 billion miles (15 billion
kilometers) away from the sun.

The Voyager spacecraft were built by NASA's Jet Propulsion Laboratory in Pasadena, Calif., which
continues to operate both. JPL is a division of the California Institute of Technology. The Voyager
missions are a part of the NASA Heliophysics System Observatory, sponsored by the Heliophysics
Division of the Science Mission Directorate in Washington. For more information about the Voyager
spacecraft, visit: http://www.nasa.gov/voyager .

For more information about NASA media events at the American Geophysical Union meeting, visit:
http://www.nasa.gov/agu .

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