Maandag 16 september 2013
They Left Theirs Too But Long Time Before It
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.
Credits:
Production
editor: Dr. Tony Phillips | Credit: Science@NASA
Related
Links and More Information:
Voyager Interstellar
Mission -- home page from JPL
JPL
built and operates the twin Voyager spacecraft. The Voyagers Interstellar
Mission is a part of NASA's Heliophysics System Observatory, sponsored by the
Heliophysics Division of NASA's Science Mission Directorate in Washington.
NASA's Deep Space Network, managed by JPL, is an international network of
antennas that supports interplanetary spacecraft missions and radio and radar
astronomy observations for the exploration of the solar system and the universe.
The network also supports selected Earth-orbiting missions.
The
cost of the Voyager 1 and Voyager 2 missions -- including launch, mission
operations and the spacecraft’s nuclear batteries, which were provided by the
Department of Energy -- is about $988 million through
September.
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