IBEX mapping Solar System's unseen boundary

BY KULVINDER SINGH CHADHA

ASTRONOMY NOW

Posted: 19 January, 2009

NASA’s Interstellar Boundary Explorer (IBEX) mission has
begun building the first maps of the edge of our Solar System, something that has never been done until now.

IBEX is an ingenious spacecraft that uses energetic neutral atom (ENA) imaging to create images of the interactions between the one million kilometre-per-hour solar wind (blown out in all directions by the Sun) and the low-density material that lies between the stars (the interstellar medium). The solar wind 'blows out' a bubble in the intersetallr medium, called the heliosphere. The boundary where the heliosphere meets the interstellar medium is considered to be the end of the Solar System environment, and the beginning of interstellar space.

The interactions at the boundary create neutral atoms, some of which rebound back towards Earth, and it is these that IBEX uses in its map-creation. They rebound from the edge with speeds between 100 kilometres and 36 million kilometres per hour. Each ENA sensor uses a charge-exchange process that converts incoming neutral atoms into charged ions, enabling them to be analyzed.

"We are seeing fabulous initial results from IBEX, but just as
artisans use looms to build up colourful textiles by weaving one thread at a time, the IBEX sensors also need time — six months — to build up a complete map of the sky," says Dr. David McComas, IBEX principal investigator and senior executive director of the Space Science and Engineering Division at Southwest Research Institute. "So far, the intricate pattern of this fascinating interaction is only just beginning to disclose itself to us."

IBEX's initial mapping of the boundary between the heliosphere and the interstellar medium, using the high-speed neutral atoms originating from the boundary (click for larger image). Image: Southwest Research Institute.

IBEX’s sensors look out from opposite sides of the spacecraft, perpendicular to the craft’s Sun-orientated spin axis. As IBEX spins at four revolutions per minute, the incoming ENAs fill in the pixels to gradually build a circular swath that appears as a crescent on the map. As the spacecraft's spin axis tracks the Sun, the swaths move across the sky to complete the image in the way McComas describes.

IBEX will not only enable researchers to examine the dynamics of the outer heliosphere, it will also address a serious issue facing manned exploration by studying the region that shields Earth from the Galactic cosmic rays.

"The space physics community is holding its collective breath waiting for these maps, which will provide a much deeper understanding of the Sun's interaction with the Galaxy," says McComas. "We expect the first complete image, due this summer, to tell us a great deal about the heliosphere's fundamental nature."

McComas will give a talk today at the ‘Voyagers in the
Heliosheath’ meeting, held in Kauai, Hawaii, on IBEX.