Voyager 2 sent First Scientific Data on Interstellar Space

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Scientists estimated that Voyager 2 left the solar system late a year ago, but the latest findings - published this week in the journal Nature - offer confirmation.

It entered interstellar space, and now, a year later, scientists have published five papers in Nature Astronomy about their findings. When Voyager 1 crossed, "we were surprised to find that the direction of the magnetic field was not what we had expected when we were outside, and with Voyager 2 we are finding a very similar result".

"The two Voyagers will outlast Earth", Kurth said. This transition is usually marked by plasma change that Voyager 1's instruments had difficulty measuring. That transition from inside to outside the bubble took less than 1 day, the project scientists said, just like with Voyager 1. Voyager 1, on the other hand, didn't see such leakage. Both are now traversing the Milky Way galaxy's interstellar medium, a chillier region filling the vast expanses between the galaxy's stars and planetary systems.

In November 2018, NASA's Voyager 2 spacecraft became only the second human-made object to cross the outer edge of the Sun's heliosphere, the bubble of space filled by the solar wind. The changes confirmed that the probe had entered a new region of space.

And, because Voyager 1's plasma instrument was broken when it crossed the heliopause six years earlier, it's the first time scientists have been able to study a full in-situ dataset of the plasma profile of this important boundary.

"When the two Voyagers were launched, the space age was only 20 years old", says Stone. The "bubble" of the heliosphere is continuously "inflated" by plasma, a gas of charged particles or ions, coming from the Sun.

Voyager 2, which left the solar system with its instruments intact, completed the set of data.

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Voyager 2 has just sent back data proving that it has also crossed the heliopause, and it had a fully functional plasma spectrometer.

Voyager 2's entry into the ISM occurred at 119.7 astronomical units (AU), or more than 11 billion miles from the Sun.

Voyager 2's cosmic ray instrument also detected something Voyager 1 didn't - evidence of a layer between the heliopause and interstellar space where the two 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".

The shape depends, in a complex way, on the relative strengths of the magnetic fields inside and outside of the heliosphere, and the latest measurements are suggestive of a more spherical form.

Voyager 2's encounter with the boundary has always been anticipated by eager scientists keen to get their hands on data transmitted back by the probe, as although Voyager 1 did send some data back, somewhere en route in 1980 the probe's plasma instrument was damaged which meant that it couldn't gather complete data on this breakthrough moment. A period of low solar activity should have pulled the heliopause back a bit during Voyager 2's crossing a year ago. With a supersonic wind of ionised plasma, the Sun carves out a bubble of space around the Solar System. Voyager 2 observed that the plasma outside the heliosphere is slightly warmer than expected, which could also indicate it is being compressed.

This has been concluded based on plasma density readings from the plasma wave apparatus mounted on the vehicle. Its 22.4-watt transmitter has a power equivalent to a fridge light, which is more than a billion billion times dimmer by the time it reaches Earth and is picked up by Nasa's largest antenna, a 70-metre dish. "They are of their grasp orbits around the galaxy for 5 billion years or longer, and the probability of them working into something else is almost zero". The team hopes the Voyagers will reach the distant point where space is undisturbed by the heliosphere before they run out of fuel.

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