In the murky boundary between our solar system and the rest of the galaxy, scientists have spotted a bright band of surprising high-energy emissions.
The results come from the first all-sky map created by NASA's new Interstellar Boundary Explorer (IBEX) spacecraft, which launched in October 2008. While orbiting Earth, IBEX monitors incoming neutral atoms that originate billions of miles away at the solar system's edge to learn about the interaction between the sun and the cold expanse of space.
"The IBEX results are truly remarkable, with emissions not resembling any of the current theories or models of this never-before-seen region," said David McComas, IBEX principal investigator at the Southwest Research Institute in Texas. "We expected to see small, gradual spatial variations at the interstellar boundary, some 10 billion miles away. However, IBEX is showing us a very narrow ribbon that is two to three times brighter than anything else in the sky."
This ribbon of energy lies at the very edge of the solar system, where the bubble of charged particles streaming from the sun finally peters out. This bubble is called the heliosphere, and it encompasses the region of space dominated by the sun's influence.
The edge of the solar system
At the boundary of the heliosphere, the sun's positively-charged particles interact with neutral atoms drifting in from interstellar space. When these particles meet, an electron may hop over from a neutral atom to a charged one, called an ion. The result: the charged particle becomes neutral. IBEX detects these fast-moving neutral particles and traces their paths back to the solar system's edge to create a picture of this chaotic frontier.
"We're just now getting a handle on the interaction of the surrounding interstellar medium with the heliosphere, and that's providing us with the big picture," said mission co-investigator Eberhard Möbius of the University of New Hampshire.
The mission scientists said they were surprised to discover the striking band in IBEX's sky maps, because no models had predicted such a pattern beforehand.
McComas said when he first saw the IBEX results he thought, "'Something's wrong,' It was quite a long time before we convinced ourselves that we were right," he said.
The bright ribbon appears to be shaped by the direction of the interstellar magnetic field outside the heliosphere. Scientists think this suggests that the galactic environment just outside the solar system has far more influence on the structure of the heliosphere than previously believed.
"[The ribbon is] aligned by and dominated by the external magnetic field," McComas said in a briefing Thursday. "That's a huge clue as to what's going on. But still we're missing some really fundamental aspect of the interaction — some fundamental physics is missing from our understanding."
The boundary of the solar system was first explored by the Voyager 1 spacecraft in 2004 when it encountered an invisible shock created as the charged particles streaming off the sun hit the neutral gas from interstellar space. Its sister craft Voyager 2 followed into the solar system's edge in 2007. While these spacecraft began the exploration of this wild frontier, IBEX is now revealing a whole new picture.
"The most astounding feature in the IBEX sky maps — the bright narrow ribbon — snakes through the sky between the Voyager spacecraft, where it remained completely undetected until now," McComas said.
The new IBEX results will be published in the Oct. 16 issue of the journal Science.