We thought as much, but now we know as
much. We are clearly outside the bow
wave and moving through true interstellar space which correctly is hardly
homogenous locally. We will now get an
additional seven years of monitoring to give us a good representation that will
have to last us until we get seriously faster and capable.
We can wait for this.
In the meantime, our models of the Solar
system are no longer based on educated guesswork but on hard data on
boundaries.
Voyager 1 Has Left the
Solar System
Sept. 12, 2013: NASA's
Voyager 1 spacecraft officially is the first human-made object to venture into
interstellar space. The 36-year-old probe is about 12 billion miles (19 billion
kilometers) from our sun.
New and unexpected
data indicate Voyager 1 has been traveling for about one year through plasma,
or ionized gas, present in the space between stars. Voyager is in a
transitional region immediately outside the solar bubble, where some effects
from our sun are still evident. A report on the analysis of this new data, an
effort led by Don Gurnett and the plasma wave science team at the University of
Iowa, Iowa City, is published in Thursday's edition of the journal Science.
Now that we have new, key data, we believe this
is mankind's historic leap into interstellar space," said Ed Stone,
Voyager project scientist based at the California Institute of Technology,
Pasadena. "The Voyager team needed time to analyze those observations and
make sense of them. But we can now answer the question we've all been asking --
'Are we there yet?' Yes, we are."
Voyager 1 first detected the increased pressure
of interstellar space on the heliosphere, the bubble of charged particles
surrounding the sun that reaches far beyond the outer planets, in 2004.
Scientists then ramped up their search for evidence of the spacecraft's
interstellar arrival, knowing the data analysis and interpretation could take
months or years.
Voyager 1 does not have a working plasma sensor,
so scientists needed a different way to measure the spacecraft's plasma
environment to make a definitive determination of its location. A coronal mass
ejection, or a massive burst of solar wind and magnetic fields, that erupted
from the sun in March 2012 provided scientists the data they needed. When this
unexpected gift from the sun eventually arrived at Voyager 1's location 13
months later, in April 2013, the plasma around the spacecraft began to vibrate
like a violin string. On April 9, Voyager 1's plasma wave instrument detected
the movement. The pitch of the oscillations helped scientists determine the
density of the plasma. The particular oscillations meant the spacecraft was
bathed in plasma more than 40 times denser than what they had encountered in
the outer layer of the heliosphere. Density of this sort is to be expected in
interstellar space.
The plasma wave science team reviewed its data
and found an earlier, fainter set of oscillations in October and November 2012.
Through extrapolation of measured plasma densities from both events, the team
determined Voyager 1 first entered
interstellar space in August 2012.
"We literally jumped out of our seats when
we saw these oscillations in our data -- they showed us the spacecraft was in
an entirely new region, comparable to what was expected in interstellar space,
and totally different than in the solar bubble," Gurnett said. "Clearly
we had passed through the heliopause, which is the long-hypothesized boundary
between the solar plasma and the interstellar plasma."
The new plasma data suggested a timeframe
consistent with abrupt, durable changes in the density of energetic
particles that were first detected on Aug. 25, 2012. The Voyager team
generally accepts this date as the date of interstellar arrival. The charged
particle and plasma changes were what would have been expected during a
crossing of the heliopause.
"The team’s hard work to build durable
spacecraft and carefully manage the Voyager spacecraft's limited resources paid
off in another first for NASA and humanity," said Suzanne Dodd, Voyager
project manager, based at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
"We expect the fields and particles science instruments on Voyager will
continue to send back data through at least 2020. We can't wait to see what the
Voyager instruments show us next about deep space."
Voyager 1 and its twin, Voyager 2, were launched
16 days apart in 1977. Both spacecraft flew by Jupiter and Saturn. Voyager 2
also flew by Uranus and Neptune. Voyager 2, launched before Voyager 1, is the
longest continuously operated spacecraft. It is about 9.5 billion miles (15
billion kilometers) away from our sun.
Voyager mission controllers still talk to or
receive data from Voyager 1 and Voyager 2 every day, though the emitted signals
are currently very dim, at about 23 watts -- the power of a refrigerator light
bulb. By the time the signals get to Earth, they are a fraction of a
billion-billionth of a watt. Data from Voyager 1's instruments are transmitted
to Earth typically at 160 bits per second, and captured by 34- and 70-meter
NASA Deep Space Network stations. Traveling at the speed of light, a signal
from Voyager 1 takes about 17 hours to travel to Earth. After the data are
transmitted to JPL and processed by the science teams, Voyager data are made
publicly available.
“Voyager has boldly gone where no probe has gone
before, marking one of the most significant technological achievements in the
annals of the history of science, and adding a new chapter in human scientific
dreams and endeavors,” said John Grunsfeld, NASA’s associate administrator for
science in Washington. “Perhaps some future deep space explorers will catch up
with Voyager, our first interstellar envoy, and reflect on how this intrepid
spacecraft helped enable their journey.”
Scientists do not know when Voyager 1 will reach
the undisturbed part of interstellar space where there is no influence from our
sun. They also are not certain when Voyager 2 is expected to cross into
interstellar space, but they believe it is not very far behind.
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