Voyager 2 pierces the heliopause, enters interstellar space

Voyager 1 and 2 crossed the heliopause and entered interstellar space. On Nov. 5, 2018, the Voyager 2 spacecraft crossed the heliopause and entered interstellar space. Voyager 1 crossed into interstellar space in 2012. Credit: NASA/JPL-Caltech

On Nov. 5, 2018, Voyager 2 became the second spacecraft to enter interstellar space, as it passed through the heliosphere’s outer limit, known as the heliopause, NASA announced at the American Geophysical Union (AGU) fall meeting in Washington, D.C., on Monday. The spacecraft’s twin, Voyager 1, made history as the first man-made object to depart the heliosphere in 2012. Reaching interstellar space is an extraordinary feat for spacecraft that have been traveling for more than 41 years.

Voyager 1 provided data related to its passage through the heliopause — where the hot solar wind abuts the cold, dense interstellar medium — and scientists looked for a similar set of observations as Voyager 2 neared the heliopause. Their task was eased by input from the Plasma Science Experiment, an instrument that had stopped working on Voyager 1 in 1980, as it passed near Saturn, Edward Stone of Caltech told EARTH. Stone has been the Voyager mission’s project scientist since its inception in the 1970s.

Stone told reporters at the AGU meeting that when the Voyagers were launched, “we didn’t know how large [the heliosphere] was, we didn’t know how long it would take to get there, we didn’t know if the spacecraft could last long enough to get there.” 

To determine that Voyager 1 had exited the heliosphere in 2012, Stone said, scientists relied on three factors: an increase in the intensity of cosmic rays, which are severely limited by the heliopause; a corresponding disappearance of outbound particles from the sun that are deflected at the heliopause; and a jump in the intensity of the magnetic field emanating from the Milky Way galaxy, outside the heliosphere. For Voyager 2, these three factors came together convincingly on Nov. 5, 2018, Stone said.

Voyager 2 by the numbers. Artist's concept of Voyager 2 along with facts about the mission. Credit: NASA

Thanks to its still-working instruments, like the Plasma Science Experiment, Voyager 2 provided the first data on plasma in the outer reaches of the heliosphere. Plasma is ionized gas consisting mainly of protons and electrons moving through the solar system. It was a long six-year wait to finally get this data, John Richardson of MIT told reporters.

The two Voyagers can now observe the local galactic neighborhood outside the heliosphere, noted Georgia Denolfo of NASA’s Goddard Space Flight Center. Actually, she said, the spacecraft are now in a new “bubble,” 100,000 times larger than the heliosphere, filled with a tenuous million-degree gas.

Stone said the two Voyagers are healthy and should keep reporting data back to Earth for years to come. As their nuclear power sources deplete, though, instruments aboard the spacecraft will be turned off, one by one, in an order to be determined as the time approaches.

Harvey Leifert

Leifert is a freelance science writer based in Bethesda, Md.

Tuesday, December 11, 2018 - 15:45

Did you know ...

The digital edition of EARTH Magazine is a free subscription for members of AGI's Member Societies.  Find out more!

EARTH only uses professional science journalists and scientists to author our content?  In this era of fake news and click-bait, EARTH offers factual and researched journalism. But EARTH is a non-profit magazine, and at least 10 times more people read EARTH than pay for it. As advertising revenues across the media decline, we need your help to ensure that we can continue bringing you the reliable and well-written coverage of earth science you know and love. Our goal is not only to inform our readers, but to inform decision makers across the economic and political spectrum about the science of our planet. So, we need your help. By becoming a subscriber or making a tax-deductible contribution to support EARTH, you can fund our writers and help make sure the world knows about our planet.

Make a contribution

Subscribe