Voyager probes detect previously unknown phenomenon in deep space

NASA’s Voyager spacecraft may be billions of miles away and over 40 years old, but it continues to important discoveries, as new research reveals.

An article published today in the Astronomical journal describes an entirely new form of electron burst, a discovery made possible by the intrepid Voyager probes. These bursts occur in the interstellar medium, a region of space in which the density of matter is extremely thin. AAs the new article points out, something funky is happening to the electrons in cosmic rays that are making their way through this remote region: TThey are reflected and driven at extreme speeds by advancing the shock waves produced by the sun.

In itself, this process, in which the shock waves push the particles, is nothing new. What is new, however, is that these electron bursts appear long before the advancing shock wave, and that it occurs in a supposedly calm region of space. The new article was co-authored by astrophysicist Don Gurnett of the University of Iowa.

Launched in 1977, Voyager 1 and Voyager 2 made huge work for the king and the country, and they always activate significant scientific work after so many years. But instead of studying the active volcanoes on Jupiter’s moon Io or taking glorious photos of Saturn’s rings, these probes are now studying the uncharted waters beyond the heliopause – the area between hot solar plasma and the colder interstellar medium at the edge of the solar system.

Voyager 1 is currently 14.1 billion kilometers away, and Voyager 2 is 11.7 billion kilometers away (the probes were launched within 16 days of each other, but they were sent on different paths during their respective sojourns through the solar system). Voyager 1 crossed the heliopause limit in 2012, and Voyager 2 did the same in 2018. They are currently traveling in a region called very local interstellar medium (VLISM), according to the study. Voyager probes are the most distant human-made objects of all time.

Some may quibble over the term “interstellar medium“And claim that Voyager probes are technically still inside the solar system, but Gurnett is adamant that Voyager probes do travel through interstellar space, which literally means” the middle between the stars, ” as he explained by phone. “We won that argument,” Gurnett said, “but of course I’m biased.” The gas pressure at the Voyager probe location, he said, is equal to the gas pressure we would expect to see in interstellar space. For him, this means that the probes are inside the interstellar medium.

In 2012, Gurnett among his colleagues declared that Voyager 1 traveled through interstellar space, a claim confirmed by NASA the next year.

Years ago, before NASA probes entered this region of space, “we thought it might get downright boring and nothing changes there,” Gurnett said. “But what we found out is that it’s not calm and quiet at all – the interstellar medium has some important things going on!“

As previous research has shown, stellar shock waves travel through this region of space, the result of coronal mass ejections on the Sun. These highly energetic events propel hot gases and energy into space, propelling them toward the heliopause and the interstellar medium at tremendous speeds. Even travel 1 millions of miles per hour, however, it takes more than a year for these shock waves to reach the heliopause and another half a year to reach Voyager probes, Gurnett explained. To get an idea of ​​the current spacing of the probes, it takes about 20 hours for a Voyager transmission – traveling at the speed of light – to reach Earth.

As described in the new document, these shock waves facilitate an unprecedented behavior in the interstellar medium, namely bursts of electrons appearing well in advance of the advancing shock waves.

“The study is unique in that it examines several large solar storms that pass through the bubble that the Sun sculpts in the interstellar medium and extends well beyond Pluto,” Herbert Funsten, a space scientist at Los Alamos National Laboratory which is not involved in the new study, explained in an e-mail. “Voyager spacecraft are in the interstellar medium and therefore look at the bubble – and the shocks that cross the bubble border – from the outside, providing a unique and calm place of observation that we cannot observe from the outside. inside the bubble.

Voyager probes detected these surges of energy with on-board instruments designed to detect cosmic rays (NASA was thinking about the future, and that’s exactly the sort of thing the probes were designed for).

In terms of what’s going on, electrons in VLISM bounce back and are redirected by magnetic field lines in interstellar plasma, or ionized gas.

“The magnetic field lines in the interstellar medium are almost purely straight,” Gurnett explained. “We detected the electron bursts when the shock waves first hit the magnetic field lines crossing the Voyager spacecraft – and that’s the mechanism. The shock wave just hits the magnetic field line, and there is a jump in the shock level, which reflects and energizes some of the electrons from the cosmic rays.

Indeed, this interaction seems to accelerate the electrons, pushing them in front of the advancing shock wave. The authors of the study qualify this phenomenon as “interstellar shocks”. As a result, the swollen electrons travel about 670 times faster than the shock waves that originally pushed them towards heliopause, which means they are accelerated to nearly relativistic speeds. Gurnett likened this phenomenon to a game of ping-pong, in which the ball is the electron and the shock in the magnetic field is the paddle.

Interestingly, the probes also detected the shock waves themselves, which appeared between 13 and 30 days after the electron peaks.

“It’s like seeing the light reflected off the cloud from a distant explosion, then hearing the boom later,” Funsten said. “The time it takes to see the cloud and hear the boom provides important information about the properties of the interstellar medium and the properties of the shock wave penetration into the interstellar medium.”

Astronomers described the shock waves pushing electrons forward, but these interactions were at the location of the shock wave. Here, the electron bursts occur before the shock, which was not seen before, says Gurnett.

“It’s a brand-new mechanism – shock accelerates electrons, ”he says. “But the shock hasn’t hit the spacecraft yet, so it’s a precursor, which we call the precursor.”

Funsten said these events are rare, but they provide “tantalizing clues” to the effects of these shocks on the interstellar medium. However, “more data will be needed to better understand these findings,” he said, including more data from Voyager 2, “which has not been in the interstellar medium for a long time,” as well as the upcoming NASA’s IMAP mission (Interstellar Mapping and Acceleration Probe), scheduled to launch in 2024.

The new paper could improve our understanding of the complex interactions between shock waves and cosmic radiation, not just on the outskirts of our neighborhood but also around other stars, including exploding stars. These findings could also shed new light on the types of exposures astronauts should expect when working in space.

A note to Voyager probes: keep doing what you’re doing. YesYou are awesome.