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NASA’s Voyager spacecraft may be billions of kilometers away and over 40 years old, but they are still making significant discoveries, new research reveals.
An article published today in the Astronomical Journal describes an entirely new form of electron blast, a discovery made possible by the intrepid Voyager probes. These explosions are happening in the interstellar medium, a region of space where the density of matter is painfully thin. As the new paper points out, something strange is happening to cosmic ray electrons making their way through this remote area: they are reflected and boosted at extreme speeds by advancing the shock waves produced by the Sun.
By itself, this process, where shock waves push particles, is nothing new. The novelty, however, is that these electron bursts are appearing long before the advancing shock wave and are happening in a supposedly quiet region of space. The new paper was written in collaboration with Iowa University astrophysicist Don Gurnett.
Launched in 1977, Voyager 1 and Voyager 2 have done extraordinary work for the king and the country and continue to enable significant scientific work after so many years. But instead of studying 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 zone between the hot solar plasma and the coldest interstellar medium at the outer borders. of the solar system.
Voyager 1 is currently at 22.6 billion kilometers and Voyager 2 at 17.9 billion kilometers (the probes were launched within 16 days of each other, but were sent on different trajectories during their respective stays across the solar system). Voyager 1 crossed the heliopause border in 2012 and Voyager 2 did the same in 2018. According to the study, they are currently traveling through a region called VLISM (Very Local Interstellar Medium). Voyager probes are the most distant human-made objects ever.
Some may quibble over the term “interstellar medium” and claim that the Voyager probes are still technically within the solar system, but Gurnett is adamant that the Voyager probes are actually traveling through interstellar space, which literally means “middle of the stars. “, as he explained on the phone. “We won that argument,” Gurnett said, “but obviously I’m biased.” The gas pressure at the location of the Voyager probes, 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 of his colleagues said Voyager 1 passed into interstellar space, a claim confirmed by NASA the following year.
Years ago, before NASA spacecraft entered this region of space, “we thought it could get downright boring, and nothing changes out there,” Gurnett said. “But what we found is that it is by no means silent and quiescent – the interstellar medium has important things going on!”
As previous research has shown, stellar shockwaves are traveling in this region of space, the result of coronal mass ejections on the Sun. These highly energetic events push hot gases and energy into space, projecting them towards the heliopause and the medium. interstellar at incredible speeds. Even traveling over 1.6 million kilometers per hour, however, it takes more than a year for these shock waves to reach the heliopause and another half a year to reach the Voyager probes, Gurnett explained. To get an idea of how far away the probes are at this time, it takes about 20 hours for a Voyager transmission – traveling at the speed of light – to reach Earth.
As the new paper describes, these shockwaves are facilitating never-before-seen behavior in the interstellar medium – bursts of electrons that appear long before advancing shockwaves.
“The study is unique in that it examines several large solar storms that hit the bubble the Sun carves from the interstellar medium and extends far beyond Pluto,” said Herbert Funsten, a space scientist at Los Alamos National Laboratory who is not involved with the new. study, explained in an email. “The Voyager spacecraft are located in the interstellar medium and therefore are looking at the bubble – and the shocks that cross the bubble boundary – from the outside, providing a unique and silent observation place that we cannot observe from inside the bubble.”
The Voyager probes detected these bursts of energy with onboard instruments designed to detect cosmic rays (NASA was thinking ahead, and that’s exactly the kind of thing the probes were designed for).
In terms of what is happening, the electrons in the VLISM bounce and are redirected by the magnetic field lines in the interstellar plasma, or ionized gas.
“The magnetic field lines in the interstellar medium are almost purely straight lines,” Gurnett explained. “We detected the electron bursts when the shock waves first touched the magnetic field lines running through the Voyager spacecraft – and that’s the mechanism. The shock wave barely touches the magnetic field line and there is a jump to the shock, which reflects and energizes some of the electrons of the cosmic rays. “
Indeed, this interaction appears to accelerate the electrons, pushing them in front of the advancing shock wave. The authors of the study refer to this phenomenon as “interstellar tremors”. As a result, the boosted electrons move about 670 times faster than the shock waves that originally propelled them towards the heliopause, meaning they are accelerated to near relativistic speeds. Gurnett compared this phenomenon to a game of pingpong, 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 13 to 30 days after the electron spikes.
“This is analogous to seeing the light reflected from the cloud of a distant explosion and 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 punch-through properties of the shock wave in the interstellar medium.”
Astronomers have already described shockwaves that push electrons earlier, but those interactions were in the position of the shockwave. Here, the electron bursts are happening before the shock, which hasn’t been seen before, Gurnett said.
“This is a brand new mechanism – the shock accelerates electrons,” he said. “But the shock hasn’t reached the spacecraft yet, so it’s a precursor, which we call a preliminary shock.”
Funsten said these events are rare, but provide “tantalizing clues” to the effects of these shocks on the interstellar medium. However, “more data will be needed to better understand these results,” he said, including more data from Voyager 2, “which hasn’t been in the interstellar medium for long,” as well as NASA’s upcoming IMAP (Interstellar Mapping and Acceleration Probe) mission. ), which is scheduled to launch in 2024.
The new paper could improve our understanding of the complex interactions between shock waves and cosmic radiation, not only in the suburbs of our neighborhood but also around other stars, including exploding stars. These findings could also shed new light on the types of exposure astronauts should expect while working in space.
A note for the Voyager probes: keep doing what you are doing. You are fantastic.
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