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Voyager 2 joins its sibling in the interstellar medium

Image credit: pa

Nasa has received the first reports back from the Voyager 2 probe, which recently became only the second man-made object to leave the solar system after its sibling Voyager 1 six years ago.

The probe originally departed the Earth in 1977 with a mission to study the outer planets including Jupiter, Saturn, Uranus and Neptune. It is the only spacecraft to have visited the latter two.

Although its primary mission finished in 1989, scientists have kept in touch with it in order to learn more about the furthest reaches of the solar system and beyond.

While Voyage 1 left the solar system six year ago, its slower trajectory has meant that Voyager 2 is only just entering the interstellar medium - the region outside the heliopause made up of gas, dust and cosmic rays.

Both craft have long-lasting nuclear-powered batteries and continue to communicate with the US space agency across billions of miles.

voyager 2

Image credit: pa

Scientists studying the information beamed back by Voyager 2 say they noted a “definitive jump” in the density of the plasma in interstellar space.

This jump was detected by one of the instruments on the probe and is evidence that it is making its way “from the hot, lower-density plasma characteristic of the solar wind to the cool, higher-density plasma of interstellar space”.

The readings match those of Voyager 1 when it made its own jump despite its different trajectory. This suggests that the heliosphere is symmetric said Bill Kurth, a research scientist at the University of Iowa, “at least at the two points where the Voyager spacecraft crossed.”

The astronomers also hope to gain a better understanding of how solar winds and interstellar winds interact.

Dr Edward Stone, a professor of physics at the California Institute of Technology and former director of the Nasa Jet Propulsion Laboratory, said: “We are trying to understand the nature of the boundary where these two winds collide.” He added that the spacecraft may lose power entirely in the next five years.

The researchers suggest that the interstellar medium near the heliopause is hotter than expected, with a temperature of around 30,000-50,000K (29,000-49,000°C).

In another study, a different team reported the presence of layers “on both sides of the heliopause”.

While scientists were aware of the inner layer, the presence of the outer layer became evident only after Voyager 2 crossed into interstellar space.

The researchers said evidence gathered by both probes show that the interstellar medium, along with the heliopause and the interstellar magnetic fields, “form a complex interconnected dynamical system”.

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