June 27, 2013
Steve Cole
Headquarters, Washington
202-358-0918
stephen.e.cole@nasa.gov
Jia-Rui C. Cook
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-0850
jccook@jpl.nasa.gov
RELEASE: 13-191
NASA'S VOYAGER 1 EXPLORES FINAL FRONTIER OF OUR 'SOLAR BUBBLE'
WASHINGTON -- Data from Voyager 1, now more than 11 billion miles from
the sun, suggest the spacecraft is closer to becoming the first
human-made object to reach interstellar space.
Research using Voyager 1 data and published in the journal Science
Thursday provides new detail on the last region the spacecraft will
cross before it leaves the heliosphere, or the bubble around our sun,
and enters interstellar space. Three papers describe how Voyager 1's
entry into a region called the magnetic highway resulted in
simultaneous observations of the highest rate so far of charged
particles from outside heliosphere and the disappearance of charged
particles from inside the heliosphere.
Scientists have seen two of the three signs of interstellar arrival
they expected to see: charged particles disappearing as they zoom out
along the solar magnetic field and cosmic rays from far outside
zooming in. Scientists have not yet seen the third sign, an abrupt
change in the direction of the magnetic field, which would indicate
the presence of the interstellar magnetic field.
"This strange, last region before interstellar space is coming into
focus, thanks to Voyager 1, humankind's most distant scout," said Ed
Stone, Voyager project scientist at the California Institute of
Technology in Pasadena. "If you looked at the cosmic ray and
energetic particle data in isolation, you might think Voyager had
reached interstellar space, but the team feels Voyager 1 has not yet
gotten there because we are still within the domain of the sun's
magnetic field."
Scientists do not know exactly how far Voyager 1 has to go to reach
interstellar space. They estimate it could take several more months,
or even years, to get there. The heliosphere extends at least 8
billion miles beyond all the planets in our solar system. It is
dominated by the sun's magnetic field and an ionized wind expanding
outward from the sun. Outside the heliosphere, interstellar space is
filled with matter from other stars and the magnetic field present in
the nearby region of the Milky Way.
Voyager 1 and its twin spacecraft, Voyager 2, were launched in 1977.
They toured Jupiter, Saturn, Uranus and Neptune before embarking on
their interstellar mission in 1990. They now aim to leave the
heliosphere. Measuring the size of the heliosphere is part of the
Voyagers' mission.
The Science papers focus on observations made from May to September
2012 by Voyager 1's cosmic ray, low-energy charged particle and
magnetometer instruments, with some additional charged particle data
obtained through April of this year.
Voyager 2 is about 9 billion miles from the sun and still inside the
heliosphere. Voyager 1 was about 11 billion miles from the sun Aug.
25 when it reached the magnetic highway, also known as the depletion
region, and a connection to interstellar space. This region allows
charged particles to travel into and out of the heliosphere along a
smooth magnetic field line, instead of bouncing round in all
directions as if trapped on local roads. For the first time in this
region, scientists could detect low-energy cosmic rays that originate
from dying stars.
"We saw a dramatic and rapid disappearance of the solar-originating
particles. They decreased in intensity by more than 1,000 times, as
if there was a huge vacuum pump at the entrance ramp onto the
magnetic highway," said Stamatios Krimigis, the low-energy charged
particle instrument's principal investigator at the Johns Hopkins
University Applied Physics Laboratory in Laurel, Md. "We have never
witnessed such a decrease before, except when Voyager 1 exited the
giant magnetosphere of Jupiter, some 34 years ago."
Other charged particle behavior observed by Voyager 1 also indicates
the spacecraft still is in a region of transition to the interstellar
medium. While crossing into the new region, the charged particles
originating from the heliosphere that decreased most quickly were
those shooting straightest along solar magnetic field lines.
Particles moving perpendicular to the magnetic field did not decrease
as quickly. However, cosmic rays moving along the field lines in the
magnetic highway region were somewhat more populous than those moving
perpendicular to the field. In interstellar space, the direction of
the moving charged particles is not expected to matter.
In the span of about 24 hours, the magnetic field originating from the
sun also began piling up, like cars backed up on a freeway exit ramp.
But scientists were able to quantify the magnetic field barely
changed direction -- by no more than 2 degrees.
"A day made such a difference in this region with the magnetic field
suddenly doubling and becoming extraordinarily smooth," said Leonard
Burlaga, the lead author of one of the papers, and based at NASA's
Goddard Space Flight Center in Greenbelt, Md. "But since there was no
significant change in the magnetic field direction, we're still
observing the field lines originating at the sun."
NASA's Jet Propulsion Laboratory, in Pasadena, Calif., built and
operates the Voyager spacecraft. California Institute of Technology
in Pasadena manages JPL for NASA. The Voyager missions are a part of
NASA's Heliophysics System Observatory, sponsored by the Heliophysics
Division of the Science Mission Directorate at NASA Headquarters in
Washington.
For more information about the Voyager spacecraft mission, visit:
http://www.nasa.gov/voyager
and
http://voyager.jpl.nasa.gov
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