Bon Voyage: From Iowa to the Final Frontier

Passing the Boundary

Until it went silent last year, operating the plasma wave instrument had for decades been a relatively straightforward task for Iowa’s scientists. Beyond turning it on and off (“and we don’t like to ever turn the instrument off,” Kurth says), the team relies on only a few commands to control the instrument. One involves operating a set of attenuators, which reduce the strength of signals like inverse amplifiers. These were installed to help the instrument sift through intense waves that the researchers expected Voyager to encounter near Jupiter. But these waves never swamped the instrument, and the attenuators have never been activated. The other command turns on a specialized receiver that has collected high-resolution data on plasma waves throughout the solar system.

PHOTO: NASA An image of a volcanic eruption on Jupiter's moon Io is captured by Voyager 1 in 1979.

Interpreting what the plasma wave instrument is collecting is much more complex. But it has led to incredible insights. In 1979, the instrument detected radio emissions from lightning in Jupiter’s atmosphere. This was the first time lightning was observed outside of Earth’s atmosphere. “Nobody really knew whether lightning could exist on other planets or not,” Kurth says. “We went to Jupiter and found it.”

In 2013, the plasma wave instrument made its largest discovery yet when it detected a dramatic change in the plasma conditions near the edge of the solar system. The dense plume of plasma emanating from the sun is known as the solar wind. This wind moves throughout a region known as the heliosphere. The heliosphere is essentially a big bubble of plasma that contains Earth and its planetary neighbors and extends roughly three times the distance of Pluto into space. What lies outside the heliosphere is known as the interstellar medium.

Plasma near the sun is made up of a dense number of electrons and ions. But as the plasma moves farther from its solar source, its density gradually decreases. Kurth compares this phenomenon to an expanding gas—the farther the plasma expands, the less dense it becomes.

That’s why it was surprising when Voyager 1 was suddenly detecting a dense plasma, again at the farthest points of the heliosphere where the plasma usually peters out. This piqued the interest of the team, especially Gurnett, who had theorized that plasma waves called plasma oscillations would be found beyond the edge of the heliosphere based on radio waves Voyager 1 recorded as it soared beyond Saturn in the early 1990s. Observing these theoretical oscillations seemed like a longshot. “The probability of having Voyager fly through the right region of space at the right time to actually detect them seemed slim to none,” Kurth says.

PHOTO: UI DEPARTMENT OF PHYSICS AND ASTRONOMY From left, UI scientists Fred Scarf, Don Gurnett, and Bill Kurth conduct their work as Voyager plasma wave subsystem investigators in 1986.

In those days, Kurth made a habit of sifting through the plasma wave data at night when it arrived from NASA’s Jet Propulsion Lab in California. He remembers that April night when the high plasma density readings came through and knowing “within 10 seconds what they meant.” The next day he shared the data with Gurnett, whose theory had been validated.

The increase in plasma density Voyager was recording was not seismic. For example, the plasma density was actually much weaker than it is near Earth. But the density was at least 50 times as dense as those usually found in the outer heliosphere. Combined with other evidence—like the increase in cosmic galactic rays, which originate outside the solar system—these density readings provided “the last piece of the puzzle that convinced us that we had crossed into the interstellar medium,” Kurth says.

Voyager 1 had become the first spacecraft to pass through the heliopause, the boundary that separates the heliosphere bubble from interstellar space. Gurnett, Kurth, and their colleagues published the update in the journal Science in September 2013, and news that Voyager had entered the final frontier captivated audiences around the world in a similar vein to the press Van Allen once received. “It was one of the greatest scientific events of my career,” Gurnett recalled in 2017. “We were there at the beginning of discovery.”

PHOTO: NASA/JPL-CALTECH Voyager's components include a high-gain antenna, the body of the craft known as "the bus," and a gold-plated phonograph with images and recordings from Earth (see sidebar).

The Journey Continues

For most of the next decade, the Voyagers sent back a steady stream of scientific data collected where no spacecraft had been before.

Crossing this cosmic chasm takes quite a bit of time and a multitude of powerful radio dishes. But the insights are well worth the wait for Jaynes, who views the mission as “the shining example of our desire to reach out and discover what is elsewhere in the universe.” She was working as a post-doc on the Van Allen radiation belts at the University of Colorado when Kurth and Gurnett determined that Voyager 1 had entered interstellar space. From her office in Iowa’s Van Allen Hall, Jaynes now serves as a co-investigator on the Voyager mission with Kurth, who took over the principal investigator role after Gurnett’s death. Once the data makes it back to Earth, the UI researchers work with their partners at NASA and other institutions to understand the instrument’s readings.

These readings became impossible to decipher when Voyager 1 experienced an anomaly. The spacecraft usually beamed its data to Earth in binary codes of ones and zeroes. But beginning in November 2023, Voyager 1 began sending repeating patterns of unusable code back to Earth, leading many researchers to worry that the aging spacecraft had finally reached the end of its mission.

While the spacecraft had lasted nearly 10 times longer than initially thought, NASA scientists were not ready to let them drift into the void. Researchers at the Jet Propulsion Lab worked tirelessly to pinpoint the issue causing the disconnect.

The NASA team initially sent commands aimed at rebooting Voyager 1’s computer systems. This past March, they located the region of the spacecraft’s data system that appeared to be producing the jumbled data. An engineer was able to decode the signal and access the data system’s entire memory. This helped the team locate the corrupted region of memory, which was stored on a single chip that was either worn down or exposed to damaging radiation. Because they couldn’t replace the chip from 15 billion miles away, the team programmed around the infected memory to restore the system’s ability to collect and send data to Earth.

“[Voyager 1 and 2] have shown that nature is so much more inventive than our minds are.” —Bill Kurth

On April 20, the team received the first coherent data from Voyager 1 in five months. “It is just amazing that they were able to recover it from this anomaly,” Jaynes says. Since the recovery, Voyager 1 has continued to collect scientific data.

The data from Voyager 1 is crucial to understanding cosmic conditions outside the heliosphere. Recently, the plasma wave instrument has provided insights into charged dust particles that float throughout space, which are scarcer in interstellar space than inside the heliosphere.

To Kurth, the Voyagers have already outpaced any expectations, and not just because they have outlived their initial lifespan by more than 41 years. These spaceships have provided insights into the basic building blocks of science itself.

“They have shown that nature is so much more inventive than our minds are,” Kurth says. “We found situations in the outer solar system and the interstellar medium that we just hadn’t fathomed before, which is the reason we do missions of discovery.”

Deciphering Voyager data is paramount. While NASA was able to reconnect with Voyager 1 after its anomaly, these aging spacecraft will not be reachable forever. Voyager 1 and 2 both are powered by a limited power supply of decaying plutonium. Once that power runs out—NASA scientists have their fingers crossed that it will be after 2027 for the 50th anniversary of the launch—the Voyagers will fall silent as they fade into the final frontier. But the data they leave behind will continue to guide the Earthlings stretching out for the stars.

PHOTO COURTESY Jack Tamisiea

Jack Tamisiea is a science writer based in Washington, D.C., who covers natural history and environmental issues. Tamisiea’s work has appeared in The New York Times, National Geographic, Scientific American, Hakai Magazine, Johns Hopkins Magazine, and many others. Tamisiea is also the son of Iowa alumnus John Tamisiea (87BBA) and grew up an avid Hawkeye fan.