Voyager 1 is the first spacecraft to reach interstellar space. It
originally was launched (along with Voyager 2) in 1977 to explore the
outer planets in our solar system. However, it has remained operational
long past expectations and continues to send information about its
journeys back to Earth.
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| Artist rendering of Voyager1 |
The spacecraft officially entered interstellar space in August 2012,
almost 35 years after its voyage began. The discovery wasn't made
official until 2013, however, when scientists had time to review the
data sent back from Voyager 1.
Voyager 1 was actually the second of the twin spacecraft to launch, but it was the first to race by Jupiter and Saturn. The images it sent back
have been used in schoolbooks and newspaper outlets for a generation.
Also on board was a special record, carrying voices and music from Earth
out into the cosmos.
Voyager 2
launched on Aug. 20, 1977, and Voyager 1 launched about two weeks later,
on Sept. 5. Since then, the spacecraft have been traveling along
different flight paths and at different speeds. The Voyager missions
were intended to take advantage of a special alignment of the outer
planets that happens every 176 years. It would allow a spacecraft to
slingshot from one planet to the next, assisted by the first planet's
gravity.
The spacecraft’s next big encounter
will take place in 40,000 years, when Voyager 1 comes within 1.7
light-years of the star AC +79 3888. (The star itself is roughly 17.5
light-years from Earth.) However, Voyager 1's falling power supply means
it will stop transmitting data by about 2025, meaning no data will flow
back from that distant location.
Entering interstellar space
Voyager 1's official departure from the solar system occurred in August
2012; the discovery was made public in a study published in Science the
following year.
The results came to light after a powerful solar eruption was recorded
in Voyager 1's plasma wave instrument between April 9 and May 22, 2013.
The eruption caused electrons near Voyager 1 to vibrate. From the
oscillations, researchers discovered Voyager 1's surroundings had a
higher density than what is found inside the heliosphere, or the region
of space in which the sun's environment predominates.
It seems contradictory that electron density is higher in interstellar space
than it is in the sun's neighborhood, but the researchers explained
that at the edge of the heliosphere, electron density is dramatically
low compared with locations nearby Earth.
Researchers then backtracked through Voyager 1's data and nailed down
the official departure date to sometime in August 2012. The date was
fixed not only by the electron oscillations, but also by its
measurements of charged solar particles.
On Aug. 25, the probe saw a 1,000-fold drop in these particles and a
9-percent increase in galactic cosmic rays that come from outside of the
solar system. At that point, it was 11.25 billion miles (18.11 billion
km) from the sun, approximately 121 times the Earth-sun distance.
Voyager 1's interstellar adventures
As of February 2018, Voyager is roughly 141 astronomical units
(sun-Earth distances) from Earth. That's roughly 13.2 billion miles, or
21.2 billion kilometers. You can look at its current distance
on this NASA website.
Since flying past the solar system's boundary into interstellar space,
Voyager 1 sent back valuable information about conditions in this zone
of the universe. Its discoveries include showing that cosmic radiation
is very intense, and demonstrating how charged particles from the sun
interact with those of other stars, said project scientist Ed Stone in a September 2017 interview.
The spacecraft's capabilities continue to astound engineers. In December 2017, NASA announced that Voyager 1
successfully used its backup thrusters to orient itself to "talk" with Earth.
These "trajectory correction maneuver" (TCM) thrusters hadn't been used
since November 1980, during Voyager's last planetary flyby of Saturn.
Since then, Voyager used its standard attitude-control thrusters to
swing the spacecraft in the right orientation to talk with Earth.
As the performance of the attitude-control thrusters began to
deteriorate, however, NASA decided to test using the TCMs to extend
Voyager 1's lifespan. That test ultimately succeeded. "With these
thrusters that are still functional after 37 years without use, we will
be able to extend the life of the Voyager 1 spacecraft by two to three
years," Voyager project manager Suzanne Dodd, also of JPL, said in a
statement.
The Voyager spacecraft each celebrated 40 years in space in 2017,
prompting celebrations from NASA and celebrities such as "Star Trek"
star William Shatner. In September 2017, Shatner
read out a message to the spacecraft
originally crafted on Twitter, by Oliver Jenkins: "We offer friendship
across the stars. You are not alone." Jet Propulsion Laboratory engineer
Annabel Kennedy then transmitted the message to Voyager 1; it was
projected to reach the spacecraft in about 19 hours.
"None of us knew, when we launched 40 years ago, that anything would
still be working, and continuing on this pioneering journey," Stone
said in a NASA statement from August 2017.
"The most exciting thing they find in the next five years is likely to
be something that we didn't know was out there to be discovered."
