Oct. 13, 2008 -- As the solar system carts around our little section of the Milky Way galaxy, it disturbs the relative calm and cold fabric of intergalactic space. Not much is known about this boundary, except that the meeting is far from sedate -- something akin to a boat slamming through water at 50,000 mph.
So far, only the Voyager probes have crossed into the boundary zone, some eight to nine billion miles from Earth, with surprising results. On Sunday, NASA plans to launch a spacecraft that for the first time will be able to map the zone -- without having to go there.
The spacecraft is known as the Interstellar Boundary Explorer, or IBEX. It works by detecting particles that were stripped of electric charges in the outer regions of the heliosphere, the solar wind-filled bubble that delineates our solar system from intergalactic space.
The particles are called energetic neutral atoms and they were discovered accidentally about 20 years ago during a mission that studied the Earth's magnetosphere and the solar wind. Instruments on the satellites to measure what should have been low background levels of energetic particles sometimes detected extra counts.
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"It wasn't random," IBEX lead scientist David McComas, with the Texas-based Southwest Research Institute, told Discovery News. "There were extra counts when the detector was pointing at Earth and when there were geomagnetic storms."
Scientists learned that these energetic neutral atoms were being generated from inside the magnetosphere and realized a similar process would occur from the solar system's magnetic bubble as well.
The neutral atoms are created when a neutral atom from interstellar space passes a positively-charged particle from the sun. When this happens, an electron can jump from one to the other, making the charged atom neutral.
The next challenge was to figure out how to put a spacecraft far enough away from Earth's magnetic field so it could find the atoms transformed by the solar system's passage through intergalactic space.
"It was this concept of having a new measuring system that created a way to look at things at a distance," McComas said. "It's amazing and interesting to see in science when a new capability arises how quickly it's grabbed onto and people realize 'Wow, we can really do something with this.'"
With a budget of $169 million, scientists had limited options for launchers. They settled on a low-cost Pegasus booster, an air-launched system created by Orbital Sciences Corp., and outfitted IBEX with a hydrazine-fueled rocket motor that can place it into an orbit that reaches a distance nearly as far from Earth as the moon.
Two-thirds of the 1,000-pound spacecraft is fuel.
"This will be quite a feat," McComas said.
IBEX will take several weeks to maneuver into position before mapping can begin. Each full-sky survey will take six months. IBEX currently is funded for two years.
"We're going to see some things that we don't understand," said IBEX program scientist Eric Christian at NASA headquarters in Washington, D.C.
Among the mission's goals are to determine how the environment may have changed over time. For example, scientists are interested in learning if galactic cosmic rays were more prevalent in the past, as higher bursts of radiation may have impacted evolution.
"We don't know how the interaction works today," Christian said.
NASA's Voyager probes were dispatched in the 1970s to survey the outer planets. Voyager 1 crossed an area known as the termination shock, the boundary region between the solar system and the intergalactic medium in 2004. Voyager 2 followed in 2007.
Both probes are headed toward the outer boundary of the solar system known as the heliopause, which is where the sun's influence ends and interstellar space begins.
So far, scientists have learned that there are cosmic rays being produced from somewhere in the heliosphere that are not coming from nova and supernova explosions and that heliosphere is not uniformly shaped. Voyager 2 hit the termination shock nearly a billion miles sooner than Voyager 1.
"Maybe there's stronger-than expected magnetic fields on the outside pushing (the heliosphere) in on the south side," McComas said. "The whole region may be deflated. Nobody ever thought we could cross that much closer in with Voyager 2."
IBEX's launch is set for Sunday from the Kwajalein Atoll, located on the Marshall Islands in the Pacific Ocean. That location is closer to the equator than mainland U.S. launch sites, which will enable the rocket to take maximum advantage of Earth's rotational spin and leave the satellite in as high an altitude as possible.
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