Voyager’s probes are still sending signals back to Earth 47 years after launch

On November 14, 2023, Voyager 1 suddenly began spewing gibberish. Until then, the spacecraft had sent its images of planets and measurements of local space plasma back to Earth for 46 years on its journey through the solar system, encoded in a radio signal. But from that autumn day on there was only a recurring series of ones and zeros.

“When I realized that we might have lost Voyager 1, I almost burst into tears,” says Kostas Dialinas, a researcher at the Academy of Athens and a member of the science team for the LECP measuring device on board Voyager 1 and its spacecraft. Its identical sibling, Voyager 2, measures charged particles in space. NASA’s Jet Propulsion Laboratory in Pasadena, Voyager’s creator, immediately formed Team TIGER, a small team of experts to quickly investigate whether Voyager 1 could still be salvaged.

A grand tour of the solar system

When NASA researchers launched Voyager 1 in 1977, they didn’t expect to still be worrying about it nearly half a century later. The goal was a “grand tour” of the solar system. Voyager 1 flew by Jupiter, Saturn and some of their moons in 1979 and 1980. Voyager 2, which departed two weeks ago, also returned images of Uranus and Neptune. Thus, the Voyagers successfully completed its mission. “The tools are designed for only four years of service, and it’s really amazing that they still work,” Dialinas says.

The science spacecraft is now well beyond Pluto’s orbit, 24.3 billion kilometers from Earth: 163 astronomical units or au (au is the distance between the Sun and Earth: 150 million km).

When they were launched—the Space Age was only twenty years old—the probes were the pinnacle of scientific and technical prowess. In the Voyager probe images, what stands out is the 3.7-metre-wide antenna dish and the 13-metre-long protrusion, with an instrument at the top that measures magnetic fields. Also on board are cameras, measuring instruments, a plutonium nuclear battery and a number of simple computers, including a Flight Data System (FDS) that encodes the measurements for transmission.

But what is the cause of the meaningless string of ones and zeros? The JPL team soon suspected that this was due to a memory chip in the FDS. It is possible that the impact of cosmic particles or natural aging damaged part of the memory, only 70 KB in total. In March, Voyager 1 was able to send a “dump” of its memory home. In fact, it turns out that 3% of his memory is broken.

This gave engineers the opportunity to come up with a refactor, moving the code to parts of memory that were still working. Updates sent on May 19. Since a radio signal takes 22.5 hours to travel, JPL engineers had to wait 45 hours to respond. “You could have heard a pin drop in the minutes before we expected the signal.” Said the Voyager scientist Linda Spilker v. American website Ars Technica.

Code restructuring

But the update worked, and was followed by a series of carefully planned FDS code refactorings and recalibration of measurement tools. On June 13, NASA’s Jet Propulsion Laboratory announced that four working instruments were returning data again: a magnetic field meter, a LECP particle meter, one for cosmic particles, and one for electrons.

“You could say that Voyager 1 has cured mild Alzheimer’s,” says Kostas Dialinas. Now welcome the miraculous recovery. After the successful planetary tour, dull times came in the 1990s for the Voyagers, which steadily made their way through the void beyond the last planet Neptune. In 1990, Voyager 1 turned around for the last time Iconography Pale blue dot-picture It shows the Earth as a single light blue pixel on a dark background.

But for a long time there was little that could be done scientifically: the measurements hardly varied. Still, few scientists regularly read new data.

Things didn’t get interesting again until 2004, when the outskirts of the solar system appeared. The Sun blows a constant stream of particles into the universe: the solar wind, which has a hand in Earth’s polar lights. This stream of particles blows a bubble around the Sun, bounded by gas in interstellar space between the stars.

This mission is so unique, they really need to keep it in the air as long as possible

The first sign of change was the passing of the “termination shock.” Although there is no sound in space, density variations in rarefied space plasma can travel at speeds of about 100 kilometers per second. Initially the solar wind flows much faster, but back pressure from the interstellar gas causes a sudden slowdown at a certain point: the terminal shock.

“Before Voyager left, researchers expected that the end shock would be close to Jupiter, which turned out to be much farther away,” Dialinas says. Only in 2004 did Voyager 1 pass the terminus shock, followed by Voyager 2 in 2007. There the density increased. Instead of about a thousand particles per cubic meter, the travelers measured two thousand.

For many years, the probe sailed through this region of relatively denser gas, the “heliosphere,” to the next stage where the solar wind stops completely under the counterpressure of interplanetary gas: the edge of the Sun. After that, the interstellar medium begins, where the flow of gas and particles from all other stars prevails together. Voyager 1 crossed these limits in 2012, and Voyager 2 followed in 2018. The heliosphere is thus like a hard-boiled egg. All planets are located in the yolk, and the boundary between the yolk and the protein is the terminating shock; The protein itself is the heliosphere, which is bounded by the heliosphere.

Voyagers also helped define this format. The probes themselves are located near the “nose” of the bulging egg, the front of the heliosphere that penetrates the interstellar plasma at a speed of about 24 kilometers per second. “We’ve thought for a long time that the heliosphere has a kind of cometary structure: a convex arc in front, and a very long tail of up to 20,000 AU in the back,” Dialinas says. In this case, there will be no solar sheath visible at the back.

There is no comet shape

But no investigations have been sent in this direction, so there is no direct picture of what is happening there. However, other measurements aboard Saturn’s Cassini probe have depicted streams of fast, chargeless “energetic neutral atoms” coming from all directions. Through their local measurements, the travelers confirmed that these particles are generated in the heliosphere. “So we know how to map the heliosheath,” Dialinas says. Since we see it from every side, The heliosphere appears to be bell-shapedThere is no comet shape.

“The Voyagers allowed us to learn how the heliosphere works,” says Verlie Sterken, a space researcher at the Swiss Federal Institute of Technology in Zurich, who researches dust in space: tiny aggregates of solid materials such as silicon and carbon, with sizes ranging from nanometers. For example, we now also know that the heliosphere is thinner than we expected.” And micrometers. This dust comes, among other things, from previously exploded stars, and plays a role in the formation of planets, as well as in other stars.

“I’m particularly interested in the interactions of dust with the heliosphere,” says Sterkin. For her, Voyager’s sensors deliver Ground truth, the only in situ measurements of the heliosphere. “My field is still new, and we don’t know a lot yet, but Voyagers has provided a first sketch of our environment.”

Both spacecraft are now in interstellar space, where the solar wind has blown and the sun is no longer visible except as a speck among thousands. But discoveries followed there too. “When we crossed the edge of the heliosphere, we thought we had escaped the Sun’s influence, but it now turns out that we were still measuring shock waves from solar flares after that point,” Dialinas says.

The moment is inevitably approaching when the flow of measurements will stop again, this time forever. Voyager’s power source, which ran on the heat of radioactive plutonium, became weaker. It is assumed that by around 2030 sending signals back home will no longer be enough. But if it had been up to Dialinas, that moment would have been postponed for as long as possible. “This mission is very unique, and they really have to keep it in the air as long as possible. Every data point we get is Valuable as hell“.

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