University of Montana Scientists, Dan Reisenfeld and Paul Janzen, to Help Map Edge of Solar System

As our sun rumbles around the galactic core at 486,000 mph – taking us along for the ride – it constantly emits particles called the solar wind. At the edge of the solar system, 100 times farther out than the distance between the sun and the Earth, this wind dies down as it hits the hydrogen and helium gas between stars. Interstellar space, it seems, is not totally empty.

This edge region, the interstellar boundary, forms a vast teardrop-shaped bow shock around our solar system as the sun moves along its orbital path. It’s not unlike a rock in a stream. Though astronomers have photographed the bow shocks around other stars, we know precious little about our own.

That may change Sunday, Oct. 19, with the launch of a NASA spacecraft called IBEX, the Interstellar Boundary Explorer. University of Montana scientist Dan Reisenfeld helped design one of two primary instruments on IBEX, which will create an all-sky map of the interstellar boundary.

Both Reisenfeld and fellow UM researcher Paul Janzen are part of the core payload team for the spacecraft.

“It’s been fast and furious,” Reisenfeld said of the three years between project approval and launch. “It’s exciting IBEX is ready to take off and get to work.”

The spacecraft will launch aboard a Pegasus rocket dropped from under the belly of an aircraft flying over the Pacific Ocean near the Marshall Islands. The Pegasus will carry IBEX 130 miles above the Earth, and then a motor will push the probe above low-Earth orbit.

“The spacecraft will have a highly elliptical orbit that goes out almost to the distance of the moon,” Reisenfeld said. “It’s an eight-day orbit. The reason for that is it needs to get beyond the Earth’s magnetosphere – this collection of energetic particles surrounding our planet – that otherwise will swamp our signal.”

The two primary instruments on the 5-foot-wide spacecraft – IBEX-Low and IBEX-Hi – detect a range of energetic neutral atoms that are energized at the boundary of the solar system. Reisenfeld designed a section of IBEX-Hi that ionizes, steers and accelerates the particles to where they can be detected.

“Dr. Janzen and I have also been very much involved with the details of how the instrument will be operated once it’s in orbit,” he said. “In addition, we have been planning how the data is going to be binned and sorted out and sent down to the ground, as well as the sequences of commands that are used to turn on and operate the instrument.”

Besides answering questions about the size and shape of the bow shock and “heliosheath” surrounding our planetary system, IBEX also may answer questions about how that region protects us from interstellar cosmic rays.

Reisenfeld said these rays are intense radiation that can damage DNA or knock out electrical gear on satellites and other spacecraft. Mainly because of the heliosheath, only about 10 percent of cosmic rays reach the inner solar system, and then the Earth’s magnetosphere offers another layer of protection that reduces the radiation further.

He said two NASA spacecraft launched in 1977, the Voyager 1 and 2 probes, have reached the heliosheath on the border of interstellar space.

Reisenfeld became involved with the IBEX project while working at the Los Alamos National Laboratory in New Mexico. His boss and mentor at that time, Dave McComas, is now the IBEX principal investigator at Southwest Research Institute in San Antonio.

The IBEX proposal was submitted in 2004 as part of NASA’s competitive Explorer Program. Five proposals were funded for a concept study, and then IBEX was finally selected to become a low-cost, rapidly developed Small Explorers spacecraft in 2005.

Reisenfeld came to UM in 2004, remaining heavily involved with NASA projects while teaching Montana students courses such as Modern Physics and Quantum Mechanics. He intends to watch the launch of IBEX at the Virginia headquarters of Orbital Sciences, the private contractor that designed the rocket that will carry the probe aloft.

Contact: Dan Reisenfeld, associate professor, UM Department of Physics & Astronomy, 406-243-6423, [email protected]

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