12 BILLION
MILES AND COUNTING—Guest Blog by NASA’s Dr. Tony Phillips--
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.
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| Voyager I finished its Jupiter duties in April, 1979 |
"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.
In February 2013, the
National Radio Astronomy Observatory's 5,000-mile-wide Very Long Baseline Array
(VLBA) made this image of Voyager 1's radio signal from interstellar space.More
"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
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.
