Voyager 2 Finds the Edge of the Heliosphere

Voyager

On Nov. 5, 2018, NASA’s Voyager 2 became the second spacecraft in history to leave the heliosphere – “the protective bubble of particles and magnetic fields created by [the Earth’s] sun. The heliosphere is 11 billion miles from Earth, which is well beyond Pluto’s orbit. Voyager 2 entered interstellar space, the region between the stars. On Nov. 4, 2019, five new research papers in the journal Nature Astronomy will describe what scientists observed during and since Voyager 2’s historic crossing.

Each paper will detail 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. Together, these findings will help scientists picture this cosmic shoreline, “where the environment created by the [Earth’s sun] ends and the vast ocean of interstellar space begins.

The Sun’s heliosphere is like a boat floating through interstellar space, both are filled with plasma. This gas has had some of its atoms stripped of their electrons. The plasma in interstellar space is colder and more dense than the heliosphere. Additionally, interstellar space contains cosmic rays, particles accelerated by exploding stars. Voyager 1 taught scientists that the heliosphere protects the planets in this solar system from more than 70 percent of the radiation from the space in between the stars.

Last year, when Voyager 2 exited the heliosphere, researchers noticed that the two energetic particle detectors saw dramatic changes: the rate of the heliospheric particles detected plummeted, but the rate of cosmic rays sky-rocketed and remained high. The changes confirmed that the spacecraft entered a new region of space.

Before 2012 when Voyager 1 reached the edge of the heliosphere, researchers were not sure how far the boundary was from the Sun. 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. It was anticipated that the edge of the heliosphere, called the heliopause, could move as the activity of the Sun changes. This is consistent with the fact that the probes encountered the heliopause at different distances from the Sun.

“The Voyager probes are showing us how our Sun interacts with the stuff that fills most of the space between stars in the Milky Way galaxy. Without this new data from Voyager 2, we wouldn’t know if what we were seeing with Voyager 1 was characteristic of the entire heliosphere or specific just to the location and time when it crossed,” states Ed Stone, project scientist for Voyager and a professor of physics at Caltech.

By Jeanette Vietti

Sources:

Jet Propulsion Laboratory: Voyager 2 Illuminates Boundary of Interstellar Space
Phys.org: 42 years on, Voyager 2 charts interstellar space
Science News: Voyager 2 reveals the dynamic, complex nature of the solar system’s edge

Image Courtesy of NASA Solar System Exploration’s Flickr Page – Creative Commons License

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