Thu, Dec 29, 2011
Scientists Not Sure Exactly When, But It's Close
The 34-year odyssey of NASA's Voyager 1 spacecraft has reached a
distant point at the edge of our solar system where there is no
outward motion of solar wind.
Now hurtling toward interstellar space 11 billion miles from the
sun, Voyager 1 has crossed into an area where the velocity of the
hot ionized gas, or plasma, emanating directly outward from the sun
has slowed to zero. Scientists suspect the solar wind has been
turned sideways by the pressure from the interstellar wind in the
region between stars.
The event is a major milestone in Voyager 1's passage through
the heliosheath, the turbulent outer shell of the sun's sphere of
influence, and the spacecraft's upcoming departure from our solar
system.
"The solar wind has turned the corner," said Ed Stone, Voyager
project scientist based at the California Institute of Technology
in Pasadena, Calif. "Voyager 1 is getting close to interstellar
space."
Our sun gives off a stream of charged particles that form a
bubble known as the heliosphere around our solar system. The solar
wind travels at supersonic speed until it crosses a shockwave
called the termination shock. At this point, the solar wind
dramatically slows down and heats up in the heliosheath.
Launched on September 5, 1977, Voyager 1 crossed the termination
shock in December, 2004. Scientists have used data from Voyager 1's
Low-Energy Charged Particle Instrument to deduce the solar wind's
velocity. When the speed of the charged particles hitting the
outward face of Voyager 1 matched the spacecraft's speed,
researchers knew that the net outward speed of the solar wind was
zero. This occurred in June of 2010, at about 10.6 billion miles
from the sun.
Scientists believe Voyager 1 will cross the heliosheath into
interstellar space in about four years.
The Voyagers were built by NASA's Jet Propulsion Laboratory,
which continues to operate both spacecraft.
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