The Voyager 1 spacecraft is on the verge of slicing into interstellar space, NASA officials said today.
Experts had thought the craft was at the solar system's edge back in 2003, but the claim was disputed.
Now team members agree that the Voyager 1, launched in 1977, is plunging through
the outer layer of the solar system, where the Sun's influence ends and the
electrified solar wind slams into the thin expanse of gas between stars.
It still has a ways to go before it becomes the first manmade object to reach
for the stars.
"Voyager has entered the final lap on its race to the edge of interstellar space, as it begins exploring the solar system's final frontier," said Edward Stone, Voyager project scientist at the California Institute of Technology in Pasadena. Caltech manages NASA's Jet Propulsion Laboratory in Pasadena, which built and operates Voyager 1 and its twin, Voyager 2.
In November 2003, the Voyager team said data indicated
the probe might
have entered the termination
shock region of the solar system. Some
scientists thought it was only approaching that tumultuous layer, however.
In fact, scientists don't know where the edge is.
They assume it moves, as changes in the speed and intensity of the solar wind
force the boundary in and out.
"The consensus of the team now is that Voyager 1, at 8.7 billion miles from
the Sun, has at last entered the heliosheath, the region beyond the termination
shock," said MIT's John Richardson, principal investigator of the Voyager plasma
science investigation.
When the solar wind meets interstellar gas, a teardrop-shaped
shockwave develops as it is slowed dramatically from an average speed of up
to 1.5 million mph (700 kilometers per second). The solar
wind, made of charged particles constantly
streaming from the Sun, becomes denser and hotter at that point.
Voyager 1 has sent back measurements of a stronger magnetic field at its current
location. That indicates the solar wind speed has decreased, scientists said.
The magnetic field does not gain overall strength, but it becomes more dense
and so stronger at any given location. As a rough analogy, consider how cars
huddle closer when highway traffic slows, researchers suggested.
The magnetic field in November 2003 had increased in strength 1.7 times compared
to previous levels. In December 2004 it jumped another factor of 2.5 and has
remained at this higher level until now.
"Voyager's observations over the past few years show that the termination shock
is far more complicated than anyone thought," said NASA scientist Eric Christian.
The leading edge of the solar system, as it orbits the Milky Way, is called
the bow
shock. It resembles the ripples of water raised by the bow of a boat. Voyager
1 still has years to go before it crosses the bow shock.
The Voyager
probes surveyed the outer planets as their primary mission. Each probe could
operate through the year 2020, NASA said today in a statement.
The twin probes are on different
paths out of the solar system. Voyager 2 is about 6.5 billion miles away.
NASA has an animation
showing Voyager approaching the solar sytem's edge.
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