UNITED STATES, WASHINGTON (OBSERVATORY SCIENCE) — In 2018, Voyager 2 became the second device in history to leave the heliosphere . At a distance of about 18 billion kilometers from Earth – far beyond the orbit of Pluto – the probe entered the interstellar space.
And now, the specialists processed the first data sent by the device from interstellar space.
In the journal Nature Astronomy, five scientific articles were published at once, each of which describes the results of the operation of existing scientific instruments – a magnetic field sensor, two instruments for detecting particles in different energy ranges and two instruments for studying plasma.
The new data, coupled with the data obtained from Voyager 1, will help to learn more about the space “coastline” – the border where the medium created by our star ends and the vast ocean of interstellar space begins.
The discoveries are associated with the heliosphere – an area of space from which the solar wind (capable of speeds up to three million kilometers per hour) displaces interstellar plasma. This area is often compared with a kind of bubble in the interstellar space.
It is worth explaining that both the heliosphere and interstellar space are filled with plasma, ionized gas. It was believed that the plasma inside the heliosphere is hotter and rarefied, and the plasma in the interstellar space immediately after the heliosphere is colder and denser. Cosmic rays , or high-energy particles, are also present in interstellar space.
When Voyager 2 left the heliosphere last year, scientists announced that two of its high-energy particle detectors recorded important changes. The speed of the “heliospheric” particles dropped sharply, and the speed of cosmic rays (which differ in their characteristics) sharply increased and remained high. These changes confirmed that the probe entered a new region of space.
Before Voyager 1 reached this boundary in 2012 , scientists did not know exactly how far it was from the Sun. Now they have a chance to find out at what distance from our star the heliosphere ended for Voyager 2, and also compare this figure with the data obtained from Voyager 1.
The fact is that two twin probes left the heliosphere in different places and at different times during the eleven-year cycle of solar activity . Meanwhile, it is the activity of the Sun that determines the parameters of the heliosphere (that is, it cannot be considered simply a sphere).
Accordingly, the researchers expected that the edge of the heliosphere, called the heliopause (the theoretical boundary where the final inhibition of the solar wind occurs), could shift as the activity of the Sun changes. The fact that two probes collided with heliopause at different distances from the Sun confirms these conclusions of theorists.
New data confirm that Voyager 2 has not yet reached the undisturbed interstellar space: like its twin, the probe is apparently located in the transition region, directly behind the heliosphere.
“Research Mission” Voyager “show us how our Sun interacts with a substance that fills most of the space between the stars in the Milky Way, – says one of the project researchers, professor of physics at the California Institute of Technology, Edward Stone. Without we wouldn’t have known this new data from Voyager 2, whether what we saw in the Voyager 1 case was characteristic of the entire heliosphere, or specific only to the place and time in which the apparatus crossed it .
Two Voyagers confirmed the experts’ assumption that the plasma in the interstellar space immediately behind the heliosphere is much denser than the plasma inside the heliosphere. Voyager 2 also measured the plasma temperature in the nearest interstellar space and confirmed that it was lower than the plasma temperature inside the heliosphere.
In 2012, Voyager 1 recorded a slightly higher than expected plasma density directly outside the heliosphere, which indicated that the plasma was compressed in this area. Instruments of Voyager 2, in turn, recorded a 20-fold jump in plasma density.
Voyager 2 also recorded a slight increase in plasma density just before it left the heliosphere. This indicates that the plasma is compressed near the inner edge of the bubble.
It is important to note that two vehicles crossed the heliopause at approximately equal distances from the Sun: 121.6 AU and 119 a.u. (one astronomical unit is equal to the average distance from the Earth to the Sun). The fact that the plasma density has changed in both cases, even though the Voyagers are located at a distance of more than 150 astronomical units from each other, suggests that heliopause is probably not much different at least in two points in space, consider scientists. However, they still do not fully understand what exactly determines this symmetry.
Experts made another interesting conclusion. If the heliosphere is like a ship sailing through interstellar space, then it looks like its body is leaking somewhat. One of the instruments of the apparatus showed, showed that a small amount of particles seeps through the boundary of the heliosphere.
At one time, Voyager 1 came close to the “bow” of the heliosphere (relative to its movement in space). Meanwhile, Voyager 2 was on the flank, and this area, according to new data, is more permeable than the one where Voyager 1 is located, experts explain.
Another important observation of Voyager 1, which is now confirmed by its twin, is associated with a magnetic field. According to new data, the magnetic field in the region immediately behind the heliopause has the same direction as the magnetic field inside the heliosphere.
Previously, having data from only one device, scientists could not say for sure whether this “alignment” was characteristic of the entire external area, or whether it was just a coincidence. The information collected by the Voyager 2 magnetometer ruled out a version of the confluence of circumstances.
Scientific articles with a more detailed description of the new data are published in the journal Nature Astronomy: first , second , third , fourth and fifth .
This science article is written and prepared by our foreign editors writing for OBSERVATORY NEWS SCIENCE from different countries around the world – material edited and published by OBSERVATORY staff in our newsroom.
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