Voyager craft approaching interstellar space

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Staff Writer
SPACE.com
1 hour, 5 minutes ago



Voyager 2's journey toward interstellar space has revealed surprising
insights into the energy and magnetic forces at the solar system's
outer edge, and confirmed the solar system's squashed shape.

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Both Voyager 1 and Voyager 2 continue to send data to Earth more than
thirty years after they first launched. During the 1990s, Voyager 1
became the farthest manmade object in space.


Each spacecraft has now crossed the edge of the solar system, known as
termination shock, where the outbound solar wind collides with inbound
energetic particles from interstellar space. The termination shock
surrounds the solar system and encloses a bubble called the
heliosphere.


"The solar wind is blowing outward trying to inflate this bubble, and
the pressure from interstellar wind is coming in," said Edward Stone,
physicist and Voyager project scientist at the California Institute of
Technology in Pasadena, Calif. He and other researchers published a
series of studies in the journal Nature this week that detail the
Voyager findings.


This way and that


Voyager 2 reached the southern edge of the solar system 7 billion
miles (76 AU) from the sun, closer than Voyager 1 which had reached
the northern edge 7.8 billion miles (84 AU) from the sun. That
confirms earlier suspicions about the heliosphere bubble being
squashed at its southern region.


The reason for that asymmetrical shape rests with an interstellar
magnetic field that puts more pressure on the southern region of the
solar system — something that may change over one hundred thousand
years as that magnetic field experiences turbulence, Stone said.


Comparing the Voyager 1 crossing in December 2004 with the Voyager 2
crossing in August 2007 allowed scientists to confirm that the second
sibling actually crossed the termination shock and passed into the
heliosheath, an outer layer of the heliosphere. But Voyager 2 also
carries more working instruments that show the termination shock in
full detail.


"We're actually seeing the shock for the first time," said John
Richardson, principal scientist for Voyager's Plasma Physics
instrument at MIT in Boston, Mass.


Voyager 1's plasma detector failed after it passed Saturn, so Voyager
2 provided the first glimpse of what happens to the solar wind's
energy as it slams into interstellar space. The solar wind travels
outwards from the sun at supersonic speeds, and at temperatures near
17,540 degrees Fahrenheit (10,000 degrees Kelvin).


Scientists had predicted that the solar wind would simultaneously slow
down and heat up to a temperature near 1.8 million degrees F (1
million degrees Kelvin), but instead found that it reached just
180,000 degrees F (100,000 degrees Kelvin) at the solar system
boundary.


Hitching a ride


The solar wind's missing energy ended up hitching a ride with
interstellar intruders, Richardson said.


Neutral atoms that flowed in from outside the solar system became
energized upon entering the heliosheath layer, and then ended up
stealing 80 percent of the energy from the solar wind. Researchers
have yet to puzzle out the significance of this.


An added mystery remains as to why the solar wind slows down early, as
though anticipating running headlong into the termination shock.
Researchers have begun looking into whether the solar wind somehow
sheds energy ahead of time.


"Somehow the solar wind knows the shock is coming before it gets
there, and theory says that shouldn't be," Richardson noted, adding
that the solar wind speed drops from its supersonic speed of about 248
miles per second (400 km/s) to 186 miles per second (300 km/s) even
before hitting the edge of the solar system. That speed falls more
noticeably to about 93 miles per second (150 km/s) after the
termination shock.


Even as researchers continue parsing the Voyager findings, both
spacecraft plow onward toward deep space — and beyond all expectations
of their original mission.


"My guess is 5 to 7 years to reach interstellar space," Stone said.
"There's a very good chance that Voyager I will send the first data
back from there."