Voyager 1—one of two sibling NASA spacecraft launched 44 years ago and now
the most distant human-made object in space—still works and zooms toward
infinity.
The craft has long since zipped past the edge of the solar system through
the heliopause—the solar system's border with interstellar space—into the
interstellar medium. Now, its instruments have detected the constant drone
of interstellar gas (plasma waves), according to Cornell University-led
research published in Nature Astronomy.
Examining data slowly sent back from more than 14 billion miles away, Stella
Koch Ocker, a Cornell doctoral student in astronomy, has uncovered the
emission. "It's very faint and monotone, because it is in a narrow frequency
bandwidth," Ocker said. "We're detecting the faint, persistent hum of
interstellar gas."
This work allows scientists to understand how the interstellar medium
interacts with the solar wind, Ocker said, and how the protective bubble of
the solar system's heliosphere is shaped and modified by the interstellar
environment.
Launched in September 1977, the Voyager 1 spacecraft flew by Jupiter in 1979
and then Saturn in late 1980. Travelling at about 38,000 mph, Voyager 1
crossed the heliopause in August 2012.
After entering interstellar space, the spacecraft's Plasma Wave System
detected perturbations in the gas. But, in between those eruptions—caused by
our own roiling sun—researchers have uncovered a steady, persistent
signature produced by the tenuous near-vacuum of space.
"The interstellar medium is like a quiet or gentle rain," said senior author
James Cordes, the George Feldstein Professor of Astronomy. "In the case of a
solar outburst, it's like detecting a lightning burst in a thunderstorm and
then it's back to a gentle rain."
Ocker believes there is more low-level activity in the interstellar gas than
scientists had previously thought, which allows researchers to track the
spatial distribution of plasma—that is, when it's not being perturbed by
solar flares.
Cornell research scientist Shami Chatterjee explained how continuous
tracking of the density of interstellar space is important. "We've never had
a chance to evaluate it. Now we know we don't need a fortuitous event
related to the sun to measure interstellar plasma," Chatterjee said.
"Regardless of what the sun is doing, Voyager is sending back detail. The
craft is saying, 'Here's the density I'm swimming through right now. And
here it is now. And here it is now. And here it is now.' Voyager is quite
distant and will be doing this continuously."
Voyager 1 left Earth carrying a Golden Record created by a committee chaired
by the late Cornell professor Carl Sagan, as well as mid-1970s technology.
To send a signal to Earth, it took 22 watts, according to NASA's Jet
Propulsion Laboratory. The craft has almost 70 kilobytes of computer memory
and—at the beginning of the mission—a data rate of 21 kilobits per second.
Due to the 14-billion-mile distance, the communication rate has since slowed
to 160-bits-per-second, or about half a 300-baud rate.
Reference:
Persistent plasma waves in interstellar space detected by Voyager 1, Nature
Astronomy (2021). DOI:
10.1038/s41550-021-01363-7
Tags:
Space & Astrophysics