Nasa probe Voyager 2 reveals cosmic findings after reaching interstellar space

Pablo Tucker
March 20, 2020

In December previous year, NASA announced the spacecraft had left the solar system, saying data returned suggested there had been a major change in the environment, with a marked increase in galactic cosmic rays and decrease in heliospheric particles from the Sun.

The heliosphere, as it is known, is a protective bubble around the solar system formed by the solar wind, a stream of extremely hot and fast electrons and protons - known as plasma - that comes roaring out of the sun's nuclear heart and sprays out into space.

It can be compared to a cosmic supertanker ploughing through space, said Edward Stone, a professor at the California Institute of Technology and lead author of one of five articles published in Nature Astronomy. The "bubble" of the heliosphere is continuously "inflated" by plasma, a gas of charged particles or ions, coming from the Sun. Despite the distinct boundary between environments, some particles from inside the "bubble" manage to escape into the interstellar space.

Determining when an object leaves the solar system is not easy.

The Sun's heliosphere is like a boat floating through interstellar space, both are filled with plasma. The plasma in interstellar space is colder and more dense than the heliosphere. The space between stars also contains cosmic rays, or particles accelerated by exploding stars. The two probes are physically identical, but they took different paths through the solar system. Voyager 2 is the second spacecraft in history to cross that border, 18 billion kilometers away from us, and dive into the the interstellar space. The changes confirmed that the spacecraft entered a new region of space. The edge of the heliosphere is known as the heliopause and beyond this is interstellar space. The two probes exited the heliosphere at different locations and also at different times in the constantly repeating, approximately 11-year solar cycle, over the course of which the Sun goes through a period of high and low activity. The edge of the heliosphere is called the heliopause.

When Voyager 1 crossed the heliopause in 2012 and measured magnetic fields inside and outside the boundary, there was no significant change in the direction of the magnetic fields.

"It implies that the heliosphere is symmetric, at least at the two points where the Voyager spacecraft crossed", said Bill Kurth, University of Iowa research scientist and a co-author on the study.

Gurnett is the principal investigator for the plasma wave instrument on both Voyager probes.

Researchers noted a definitive jump in plasma density. But scientists don't yet fully understand what is causing the compression on either side.

Another interesting conclusion was made based on the spacecraft's data: the heliosphere is leaky. Voyager 2, on the other hand, is located closer to the flank, and this region appears to be more porous than the region where Voyager 1 is located. Another surprising revelation was the magnetic field in the region just beyond the heliopause is parallel to the magnetic field inside the heliosphere. Voyager-1 crossed the Sun's limit in 2012. The craft was launched slightly ahead of its twin Voyager 1 in 1977.

The Voyagers were sent initially to study the outer planets including Jupiter, Saturn, Uranus and Neptune, but then just kept on going.

"These observations, together with the Voyager 1 observations and existing models, show that the magnetic barrier, the heliopause and the neighbouring very local interstellar medium form a complex interconnected dynamical system", writes Leonard Bulgara at NASA Goddard Space Flight Center and colleagues in another paper submitted to Nature. Voyager 1, the faster of the two probes, is now over 13.6 billion miles (22 billion kilometers) from the Sun, while Voyager 2 is 11.3 billion miles (18.2 billion kilometers) from the Sun.

The Voyager probes became world famous thanks to the gold plates they carry, full of music, sounds and images of the earth, meant as a kind of time capsule that tells the story of our world to any aliens they might encounter along the way. By comparison, light traveling from the Sun takes about eight minutes to reach Earth.

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