Signs Changing Fast for Voyager 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
http://www.jpl.nasa.gov

Jia-Rui Cook 818-354-0850
Jet Propulsion Laboratory, Pasadena, Calif.
jccook@jpl.nasa.gov

News feature: 2012-225 Aug. 3, 2012

Signs Changing Fast for Voyager at Solar System Edge

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2012-225&cid=release_2012-225

Two of three key signs of changes expected to occur at the boundary of
interstellar space have changed faster than at any other time in the last seven
years, according to new data from NASA's Voyager 1 spacecraft.

For the last seven years, Voyager 1 has been exploring the outer layer of the
bubble of charged particles the sun blows around itself. In one day, on July 28,
data from Voyager 1's cosmic ray instrument showed the level of high-energy
cosmic rays originating from outside our solar system jumped by five percent.
During the last half of that same day, the level of lower-energy particles
originating from inside our solar system dropped by half. However, in three days,
the levels had recovered to near their previous levels.

A third key sign is the direction of the magnetic field, and scientists are eagerly
analyzing the data to see whether that has, indeed, changed direction. Scientists
expect that all three of these signs will have changed when Voyager 1 has
crossed into interstellar space. A preliminary analysis of the latest magnetic field
data is expected to be available in the next month.

"These are thrilling times for the Voyager team as we try to understand the
quickening pace of changes as Voyager 1 approaches the edge of interstellar
space," said Edward Stone, the Voyager project scientist based at the California
Institute of Technology, Pasadena, Calif. "We are certainly in a new region at the
edge of the solar system where things are changing rapidly. But we are not yet
able to say that Voyager 1 has entered interstellar space."

The levels of high-energy cosmic ray particles have been increasing for years,
but more slowly than they are now. The last jump -- of five percent -- took one
week in May. The levels of lower-energy particles from inside our solar system
have been slowly decreasing for the last two years. Scientists expect that the
lower-energy particles will drop close to zero when Voyager 1 finally crosses into
interstellar space.

"The increase and the decrease are sharper than we've seen before, but that's
also what we said about the May data," Stone said. "The data are changing in
ways that we didn't expect, but Voyager has always surprised us with new
discoveries."

Voyager 1, which launched on Sept. 5, 1977, is 11 billion miles (18 billion
kilometers) from the sun. Voyager 2, which launched on Aug. 20, 1977, is close
behind, at 9.3 billion miles (15 billion kilometers) from the sun.

"Our two veteran Voyager spacecraft are hale and healthy as they near the 35th
anniversary of their launch," said Suzanne Dodd, Voyager project manager
based at NASA's Jet Propulsion Laboratory, Pasadena. "We know they will cross
into interstellar space. It's just a question of when."

The Voyager spacecraft were built by JPL, 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 .

-end-


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