The detection of cosmic rays could mean that Voyager 2 is close to interstellar space

This graph shows the position of the Voyager 1 and Voyager 2 probes in relation to the heliosphere, a protective bubble created by the Sun that extends far beyond Pluto's orbit. The Voyager 1 passed through the heliopause, or the edge of the heliosphere, in 2012. The Voyager 2 is still in the heliosheath, or the outermost part of the heliosphere. Image credit and legend: NASA / JPL-Caltech

Today, at nearly 17.7 billion kilometers from Earth, NASA's Voyager 2 spacecraft has detected an increasing amount of cosmic rays from the solar system, suggesting to scientists that the spacecraft was going to enter the interstellar space.

Launched on August 20, 1977, Voyager 2 completed a "Grand Tour" of the solar system, piloted by Jupiter, Saturn, Uranus and Neptune. His twin, Voyager 1, was launched on September 5 of the same year and piloted by Jupiter, Saturn and Titan, the largest moon of Saturn. Both spacecraft are on trajectories pulling them out of the solar system.

Voyager 2 entered the outer region of the bubble surrounding the Sun and planets, called heliosphere, in 2007. This "bubble" encompasses the magnetic fields of the Sun and planets. Its outer limit, the heliopause, marks the passage from the sphere of influence of the Sun to interstellar space.

Since August, the probe has detected a 5% increase in cosmic rays from beyond the solar system, measured by its instrument, the cosmic ray detection system, Voyager 1, conducted in May 2012 Cosmic rays consist of rapidly moving particles that are blocked by hitting the heliosphere.

Scientists at the mission said Voyager 1 had entered interstellar space in August 2012 based on its measurements of a coronal mass ejection (CME) that occurred earlier that year. A shock wave generated by the CME caused an increased vibration of the particles around the spacecraft, which allowed the scientists to measure the density of the spacecraft environment.

When they discovered that the environmental density of Voyager 1 was much higher than that of the outer heliosphere, mission scientists determined that it had entered interstellar space.

However, the place where interstellar space begins remains unclear. Voyager 1 did not leave the Oort cloud, a sphere of comets orbiting the Sun extending up to 50,000 to 200,000 astronomical units (an astronomical unit, or AU). , is equal to the average distance Earth-Sun – about 93 million miles) or 0.8 to 3.2 light years. The probe will leave the Oort cloud 14,000 to 28,000 years ago.

In addition, in 2014, two scientists from Voyager 1 claimed to believe that the spacecraft was still in the heliosphere, the region dominated by the solar wind. George Gloeckler of the University of Michigan led a study published in the journal Geophysical Research Letters that the probe would remain in the solar system until it detects a reversal of the Sun's magnetic field.

The authors pointed out that although Voyager 1 detects an increase in the level of cosmic rays beyond the solar system, no changes have been detected in the level of magnetism around the probe, indicating that it was still under the influence of the Sun.

However, in the same study, Gloeckler also stated that if Voyager 1 did not undergo magnetic field reversal by a year or two ago, scientists could conclude that it had already entered interstellar space.

Not static, the heliosphere itself could regularly contract and expand, which would result in its exit and reintegration several times.

Voyager 2 took a completely different path from his twin and was able to find the heliopause either closer or farther than Voyager 1's trip. The increase in the level of cosmic rays detected by the spacecraft therefore probably does not mean not that it is close to the heliopause.

"We're seeing a change in the environment around Voyager 2, no question," said Voyager project scientist Ed Stone of Caltech. "We will learn a lot in the months to come, but we still do not know when we will hit the heliopause. We are not there yet. It's something I can say with confidence. "

Tagged: Cosmic ray heliopause interstellar space The Voyager 1 Voyager 2 Range

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Laurel Kornfeld

Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, New Jersey, who loves writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate in Science from the Astronomy Online program at the University of Swinburne. His writings have been published online in The Atlantic, the Astronomy magazine's blog section, the British Space Conference, the 2009 IAU General Assembly Journal, The Space Reporter, and in the bulletins of various astronomy clubs. . She is a member of Amateur Astronomers, Inc., based in Cranford, New Jersey. Specially interested in the external solar system, Laurel made a short presentation at the Great World Debate 2008 held at Johns Hopkins University's Applied Physics Lab in Laurel, MD.