Defining the Edge of Space: Voyager 1 Reshapes the Edge of the Solar System

Alison K. Lanier

Three months after “Star Wars: A New Hope” appeared in theaters, Voyager 1 was launched from Earth. Thirty-eight years later, the New York Times reported that the craft is finally approaching what is commonly thought of as the edge of the known solar system.

Nvate Voyager 1 NASA, solar wind, magnetic fields, interplanetary space, outer space

Credit: Sujin Jetkasettakorn

Traveling at 124 astronomical units from Earth or 124 times the distance between the Sun and the Earth, the craft is nearing the edge of the heliosphere where the local star’s solar energy reaches its limit. Rocketing onward at 38,000 mph, Voyager 1 will be the first man-made object to leave the solar system and move into the cosmos.

In recent articles published in Science Magazine, researchers chronicled what they believed the readings from the craft indicate.

They describe this approach to the edge of the solar system as “not in any of the models,” as Ed Stone, the head of NASA’s Voyager program since 1972, told the Guardian. Stone is a professor of physics at the California Institute of Technology and the former head of NASA’s Jet Propulsion Laboratory.

Reexamining the Edge of the Cosmos: Solar Wind

Scientists’ predictions about what exactly would be the nature of the transition out of the local stellar space was not exactly cut and dried, said The New York Times. Researchers made two general, initial predictions about what the Voyager would sense at the edge of the solar system. One basic assumption—that at least seems to have held true—is the dissipation of solar wind. Solar wind, defined by NASA, is an emanation of the sun’s corona which influences magnetic fields of planets and interplanetary space.

This dissipation triggered several false alarms which seemed to indicate that the craft had already left the solar system. Last July, a dip in solar energy seemed to point to the expected dissipation proved instead to be only momentary. Another, lengthy absence of solar wind occurred in August.

“On [Aug. 25, 2012,] Voyager 1 was at 122 astronomical units when the steady intensity of low-energy ions it had observed for the last six years suddenly dropped for a third time and soon completely disappeared as the ions streamed away into interstellar space,” according to researchers in an abstract about the craft. “Although the magnetic field observations indicate that Voyager 1 remained inside the heliosphere, the intensity of cosmic ray nuclei from outside the heliosphere abruptly increased.”

Tracing the Magnetic Field

The second prediction, which follows the logic of the first, is that there would be a shift in the magnetic field observed by the craft with this dissipation of solar wind, according to The New York Times. The magnetic field, though, is staying stubbornly in place, pointing in the same direction that Voyager 1 encountered when it was known to be inside the solar system.

Scientists have solved the mystery by dubbing the area where these seemingly contradictory conditions occur as an entirely new region, the heliosheath depletion region, which Leonard Burlaga, Norman Ness, and Stone describe in the abstract to their report in Science Magazine.

“Magnetic fields measured by Voyager 1 show that the spacecraft crossed the boundary of an unexpected region five times between days 210 and [around] 238 in 2012. The magnetic field strength increased across this boundary,” according to the report. “The direction of [the craft] did not change significantly across any of the five boundary crossings; it was very uniform and very close to the spiral magnetic field direction, which was observed throughout the heliosheath. The observations indicate that [the craft] entered a region of the heliosheath, the heliosheath depletion region, rather than the interstellar medium.”

Voyager 1’s Future

Stone spoke to The New York Times about the anticipated time frame for Voyager 1 to actually achieve “interstellar medium.” He said it “could be a few months, or it could be several more years.”

The tough, little craft was not initially anticipated to last this long—almost four decades—at the time of its launch, Stone told The New York Times.

However, the Guardian reported that the craft was initially expected to reach the end of the solar system long before now. The Guardian described, in response to these raised and subsequently punctured hopes that Voyager 1 had crossed some definite and absolute boundary out of known space and into infinity, that “the solar system has no edge.”

Rather, Voyager has solidified a new image of what the furthest reaches of our solar system looks like. And that the more definite vision is of a very fuzzy, gradual shift from one region of space to another.

Moving across the next great boundary in space exploration may still be in the future, but that future is still full of undefined variables. No one knows how expansive this frontier area at the edge of the solar system is, according to Stone’s commentary in the Guardian. As the two Voyagers continue on their “Grand Tour,” the expedition’s moniker, they will continue to reshape the researchers’ understanding of the nature of space.

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