Voyager 2 enters the interstellar space after 42 years

Katie Ramirez
March 21, 2020

The Voyager 2 probe was launched on August 20, 1977, by NASA from Space Launch Complex 41 at Cape Canaveral, Florida, aboard a Titan IIIE/Centaur launch vehicle.

Instruments that remain functioning on Voyager 2. "And some of them, only about 30 per cent of what's outside, can actually reach Earth".

Each paper details the findings from one of Voyager 2's five operating science instruments: a magnetic field sensor, two instruments to detect energetic particles in different energy ranges and two instruments for studying plasma (a gas composed of charged particles).

According to the latest data analysis by scientists at the University of Iowa, the probe left the heliosphere some time ago and has been streaming through interstellar space for the last several months.

Washington D.C: More than four decades after beginning its epic journey, NASA's Voyager 2 spacecraft has crossed the elusive boundary that marks the edge of the Sun's realm and the start of interstellar space, scientists have announced.

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

"In a historical sense, the old idea that the solar wind will just be gradually whittled away as you go further into interstellar space is simply not true", said Don Gurnett, co-author of a second plasma density paper and a professor emeritus of physics and astronomy at The University of Iowa in the US.

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

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Stamatios Krimigis, a space scientist at the Johns Hopkins University Applied Physics Laboratory and the principal investigator of the mission's low-energy charged particles experiment, explained that the devices were created to last just four years, during which they would need to conduct 250,000 turns of a motor (dubbed "steps") to take measurements. Researchers still hope to better understand the farther depths of the interstellar medium, beyond regions where solar particles still leak out of the heliosphere.

"We didn't know how large the bubble was and we certainly didn't know that the spacecraft could live long enough to reach the edge of the bubble and enter interstellar space", said Prof Ed Stone, of the California Institute of Technology, who has been working on the mission since before its launch in 1977. Voyager 1 and 2 exited the heliosphere at different locations and different times in the 11-year solar cycle over the course of which the Sun goes through a period of high and low activity.

The sun consistently spews out shock waves of plasma called coronal mass ejections (CMEs), which help shape the rest of the solar system.

Scientists were also surprised that it took 80 days for Voyager 2 to cross this magnetic barrier, while its sister probe did so in less than a day.

Voyager 1 crossed into interstellar space at about 122.6 AU, but at a different point in the solar system since it had different goals and trajectories through space. 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".

Measurements published in five separate papers in Nature Astronomy reveal that Voyager 2 encountered a much sharper, thinner heliosphere boundary than Voyager 1. "It's just astonishing how fluids, including plasmas, form boundaries", Gurnett said. Some astronomers place it at the so-called Oort cloud - an area full of roaming space stones at 300 billion kilometers from the sun, which still feel the sun's gravity. The one in our heliosphere is hot and scattered, and in interstellar space, it is colder and more condensed. As they study other stars with exoplanets around them, what they learn now could be applied to other systems they discover.

The last measurement obtained from Voyager 1 was when the spacecraft was at 146 AU, or more than 13.5 billion miles from the sun. This is considered the crossing point to interstellar space. In doing so, it joins Voyager 1 - the only object to reach this far out into the universe. That transition from inside to outside the bubble took less than 1 day, the project scientists said, just like with Voyager 1. "And the probability of them running into anything is nearly zero".

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