In November 2018, after the epic, after a 41-year journey, Voyager 2 finally crossed the line that marked the limits of the Sun’s influence and entered international space. But a little investigation mission is not yet complete – it is now sending home information about space outside the solar system.
And it reveals something surprising. As Voyager 2 moves farther away from the sun, this Density Space is growing.
This is not the first time this density has increased. Voyager 1, which entered international space in 2012, received a similar density gradient at a different location.
New Voyager 2 data shows that not only is the search for Voyager 1 legal, but the increase in density could be a large-scale feature of the very local international medium (VLIM).
The edge of the solar system can be defined by some different boundaries, but the one crossed by the Voyager probe is known as a heliopause, and it is defined by the solar wind.
This is the constant supersonic wind of ionized plasma that blows in all directions from the sun, and heliopause is the point at which the external pressure of that wind is no longer strong enough to push the wind from international space.
(NASA / JPL-Caltech)
The space inside the heliopause is the heliosphere, and the space outside it is the VLIM. But the heliosphere is not a spherical field. It is more like an oval, with a solar system at one end, and behind a streaming tail; The “nose” is shown in the direction of the orbit of the solar system in the galaxy.
Both Voyagers crossed the heliopause in the nose, but with a difference in latitude of 67 degrees and 43 degrees in heliographic latitude.
The space is generally thought of as a vacuum, but it is not perfect. The density of the substance is very low, but it still exists. In the Solar System, the average proton and electron density of the solar wind is 3 to 10 particles per cubic centimeter, but it grows lower than the Sun.
Between the stars, the average electron density of the interstellar medium of the galaxy is calculated to be around 0.037 particles per cubic centimeter. And the density of plasma in the outer heliosphere is about 0.002 cubic centimeters per electron.
As Voyager probes overtook Heliop ause, their plasma wave science instruments detected the electron density of plasma by plasma oscillation.
Voyager 1 crossed the Heliopus on 25 August 2012 at a distance of 121.6 astronomical units (121.6 times the distance between the Earth and the Sun, hence about 18.1 billion km).
When it measured plasma oscillations on 232 October 2013 after crossing the Heliop ause at a distance of 122.6 astronomical units (18.3 billion km), Voyager 1 found a plasma density of 0.055 electrons per cubic centimeter.
Voyager 2, which flew a long way through Jupiter, Saturn, Uranus and Neptune, crossed the Hypos on 11 November at a distance of 119 astronomical units (17.8 billion km). It measured plasma oscillations at a distance of 119.7 astronomical units (17.9 billion) on January 30, 2019, very close to the Voyager 1 measurement, with a plasma density of 0.03 cubic centimeters per electron.
And increased density in both devices. After traveling another 20 astronomical units (૨.9 billion km) through space, Voyager 1 recorded an increase of about 0.13 electrons per cubic centimeter.
But an investigation by Voyager 2 in June 2019 found a sharp increase in density at a distance of 124.2 astronomical units (18.5 billion units) to a density of about 0.12 electrons.
Given that the Earth’s atmospheric pressure has an electron density of 10 ^ 13 per cubic centimeter of plasma, that amount may seem small, but it is significant enough to guarantee our interest – especially since it is not clear what the cause is.
One theory is that the lines of the international magnetic field become stronger as they go over the heliopause. These electromagnetic ions can cause cyclotron instability which reduces plasma from the dropping field. Voyager 2 discovered a stronger magnetic field than expected when it crossed the Heliopus.
The second principle is that the material blown by the intercropping wind should be slower as it reaches the heliops, causing a kind of traffic jam. This was probably discovered by the external solar system probe New Horizon, which chose a faint ultraviolet glow in 2018 as a result of the formation of neutral hydrogen on helioposes.
It is also possible that both disclosures play a role. The future parameters taken by both Voyager probes, continuing their journey in international space, may help to find it. But, it can be a long bet to take.
“It’s not certain,” the researchers wrote in their paper, “whether Voyagers will be able to distinguish between these two classes of models.”
We believe in you, Space Probes!
The research was published in Astrophysical Journal Letters.
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