News : NASA satellite to scan solar system's outer limits

By Will Dunham

WASHINGTON (Reuters) - NASA is preparing to launch a satellite that will study in unprecedented detail the distant regions where the outermost reaches of our solar system collide with the cold expanse of interstellar space.

The U.S. space agency said on Friday that the Interstellar Boundary Explorer, or IBEX, satellite is scheduled to be launched into high-Earth orbit on Sunday for its two-year mission from a site at Kwajalein Atoll in the south Pacific.

While interstellar space often is thought of as a vacuum, it actually contains traces of gas and dust.

The solar wind, a stream of electrically conducting gas continuously moving outward from the sun at 1 million mph (1.6 million kph), blows against this interstellar material and forms a humongous protective bubble around the solar system. This bubble is called the heliosphere.

As the solar wind reaches far beyond the planets to the solar system's outer limits, it encounters the edge of the heliosphere and collides with interstellar space. A shock wave is present at this boundary.

"These boundaries really protect us from the fairly harsh galactic environment," Boston University astronomer Nathan Schwadron, who heads science operations for the IBEX mission, said during a conference call with reporters.

NASA said IBEX will map the boundary region, which is important because it shields the solar system from dangerous galactic cosmic rays. IBEX is designed to detect atoms that are heated and thrown off from the boundary.

"Every six months, we will make global sky maps of where these atoms come from and how fast they are traveling. From this information, we will be able to discover what the edge of our bubble looks like and learn about the properties of the interstellar cloud that lies beyond the bubble," physicist Herb Funsten of the U.S. Department of Energy's Los Alamos National Laboratory, who is part of the mission, said in a statement.

NASA's two unmanned Voyager probes were the first to begin to explore this region, which begins about three times further from the sun than the orbit of the dwarf planet Pluto. Voyager 1 passed the inner boundary in 2004 and Voyager 2 crossed over last year.

"The heliosphere's boundary region is enormous, and the Voyager crossings of the termination shock, while historic, only sampled two tiny areas 10 billion miles (16 billion km) apart," NASA scientist Eric Christian said.