IBEX Uses Particles to Shed Light on the Outer Solar System
IBEX First LightThis IBEX data image shows a dark sky map with the first orbit's coincidence counts from hydrogen atoms at speeds from about 100,000 to 36 million miles per hour. Click on image for high resolution. Image credit: Southwest Research Institute What do you see when you look at the regions where the sun's influence wanes and interstellar space begins? It depends on how you look.

While many astronomers observe the wonders of the universe through the light that objects emit, some build an image using atomic particles instead.

For the first time, space physicists are building a comprehensive picture of the interactions taking place in the outer solar system—called the interstellar boundary—using particles detected by NASA's Interstellar Boundary Explorer (IBEX). "IBEX is a fantastic mission of exploration and discovery," said David McComas, of the Southwest Research Institute in San Antonio, Texas, who is the principal investigator of the IBEX mission.

The new satellite's mapping mission got under way in December 2008 when IBEX saw "first light," that moment when scientists anxiously point a telescope at its target for the first time and begin collecting photons, radio waves or, in IBEX's case, high-speed atoms.

"Like an optical or radio observatory, where the first 'on target' photons through the focal plane are called 'first light,' we now have the first energetic neutral atoms (ENAs) detected by IBEX's sensors," said Robert MacDowall, IBEX mission scientist at NASA's Goddard Space Flight Center in Greenbelt, Md.

IBEX: A Global Imager Of Our Solar System’s BoundariesArtist's impression of neutral energetic atoms. Credit: NASA GSFC.
> View a podcast about the way IBEX creates global image maps
Mapping ENAs in the farthest reaches of the solar system will give scientists a better understanding of how the sun interacts with the rest of the Milky Way galaxy, where our sun and planets reside. Interstellar boundary regions shield Earth from the most dangerous galactic cosmic rays.

IBEX's two large-aperture detectors, IBEX-Lo and IBEX-Hi, measure energetic neutral atoms as they enter the solar system at speeds from about 100,000 mph to 36 million mph. The neutral atoms undergo a charge exchange process that converts them into ions, which the detectors then measure. IBEX-Lo measures lower-energy ENAs, while IBEX-Hi detects higher-energy ENAs.

Like an artist builds a mosaic from tiny pieces of glass, IBEX will build a picture of the outer solar system particle by particle. It will take the satellite about six months to build an all-sky map of the boundary region.

"The first full slice of data from IBEX-Hi was downloaded on December 8, and IBEX-Lo came on December 15," said Eric Christian, IBEX program scientist at NASA Goddard. Science results won't come for about nine months because it will take about six months for IBEX instruments to complete their first survey "and then a lot of work needs to be done before any science results are available," said Christian.

"The first map, to be released later this summer, will reveal a much deeper understanding of the fundamental nature of this region of space," said McComas. The goal is to reveal the structure of the interstellar boundary region and, ultimately, predict how the sun influences and gets influenced by its Milky Way neighbors.

"The intricate pattern of fascinating interactions occurring at the edge of the solar system is only just beginning to disclose itself to us," said McComas. When complete, these observations will provide scientists with the most complete view of the interstellar boundary.

The IBEX mission is the latest in NASA's series of low-cost, rapidly developed Small Explorers spacecraft. Southwest Research Institute developed the mission with national and international partner participation. NASA's Goddard Space Flight Center in Greenbelt, Md., manages the Explorers Program for NASA's Science Mission Directorate in Washington.

Laura Layton
NASA’s Goddard Space Flight Center