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At the Far End of the Solar System: Space Bubbles

The twin Voyager spacecraft have beamed back a set of data that reshape our understanding of what’s happening at the farthest edges of our solar system.

The farther the magnetic field extends out from the sun, the weirder it behaves, the study suggests.

At the far end of the solar system is the heliosphere, a tunnel created by solar wind. Both Voyager spacecraft are in the heliosphere’s outermost layer now, the heliosheath, where that solar wind is slowed by high-pressured interstellar gas. Data suggest that inside the heliosheath is a sea of frenzied bubbles, sausage-like in shape, each bubble about 100 million miles wide. That’s roughly the same as the distance between the earth and the sun.

Merav Opher, a Boston University astronomer and the study’s lead author described it as “a really agitated Jacuzzi.”

The theory is based on computer modeling that analyzed electron readings from the Voyager spacecraft. Readings had found dips and swells in the amount of electrons encountered by the two spacecraft. The models indicate these variations were caused by the spacecraft moving in and out of the bubbles. 

The bubbles are believed to be part of the sun’s magnetic field: charged particles of ionized gas, which stretch and twist as they move out toward the edge of the solar system and into the heliosphere. They are caused by lines of magnetic force explosively reorganizing themselves, scientists say.   The findings were released Thursday in the Astrophysical Journal.

“We’re pretty confident [data] is telling us that there is a major change in the structure of the magnetic field,” Opher said.

Scientists ultimately want to know what happens when galactic cosmic rays and other subatomic particles from interstellar space enter our solar system via the heliosphere. “We still have to explore the details of how the galactic rays will get across the heliosphere, and how they’re going to wander through those bubbles,” said James Drake, a University of Maryland physics professor.

The bubbles cause no danger for those living on earth and no danger for the spacecraft, scientists say. “But if you’re headed to Mars, you really do have to care about the radiation environment in the heliosphere,” said Eugene Parker of the University of Chicago.

After 33 years charging through the solar system, the two Voyager spacecraft are now about 10 billion miles from Earth. Both spacecraft contain instruments that measure energetic particles and send that data back to Earth.

Next step, Opher said, is to send better instruments out to interstellar space. “Voyager was designed in the late ’60s with wonderful instruments,” she said. “But we need more sensitive instruments. We’re just scraping the surface of how sensitive is the heliosheath.”

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