WASHINGTON — NASA’s Interstellar Boundary Explorer (IBEX) has captured the best and most complete glimpse yet of what lies beyond the solar system. The new measurements give clues about how and where our solar system formed, the forces that physically shape our solar system, and the history of other stars in the Milky Way.
The Earth-orbiting spacecraft observed four separate types of atoms including hydrogen, oxygen, neon and helium. These interstellar atoms are the byproducts of older stars, which spread across the galaxy and fill the vast space between stars. IBEX determined the distribution of these elements outside the solar system, which are flowing charged and neutral particles that blow through the galaxy, or the so-called interstellar wind.
“IBEX is a small Explorer mission and was built with a modest investment,” said Barbara Giles, director of the Heliophysics Division at NASA Headquarters in Washington. “The science achievements though have been truly remarkable and are a testament to what can be accomplished when we give our nation’s scientists the freedom to innovate.”
In a series of science papers appearing in the Astrophysics Journal on Jan. 31, scientists report finding 74 oxygen atoms for every 20 neon atoms in the interstellar wind. In our own solar system, there are 111 oxygen atoms for every 20 neon atoms. This translates to more oxygen in any part of the solar system than in nearby interstellar space.
“Our solar system is different than the space right outside it, suggesting two possibilities,” says David McComas, IBEX principal investigator, at the Southwest Research Institute in San Antonio. “Either the solar system evolved in a separate, more oxygen-rich part of the galaxy than where we currently reside, or a great deal of critical, life-giving oxygen lies trapped in interstellar dust grains or ices, unable to move freely throughout space.”
The new results hold clues about the history of material in the universe. While the big bang initially created hydrogen and helium, only the supernovae explosions at the end of a star’s life can spread the heavier elements of oxygen and neon through the galaxy. Knowing the amounts of elements in space may help scientists map how our galaxy evolved and changed over time.
Scientists want to understand the composition of the boundary region that separates the nearest reaches of our galaxy, called the local interstellar medium, from our heliosphere. The heliosphere acts as a protective bubble that shields our solar system from most of the dangerous galactic cosmic radiation that otherwise would enter the solar system from interstellar space.
IBEX measured the interstellar wind traveling at a slower speed than previously measured by the Ulysses spacecraft, and from a different direction. The improved measurements from IBEX show a 20 percent difference in how much pressure the interstellar wind exerts on our heliosphere.
“Measuring the pressure on our heliosphere from the material in the galaxy and from the magnetic fields out there will help determine the size and shape of our solar system as it travels through the galaxy,” says Eric Christian, IBEX mission scientist, at NASA’s Goddard Space Flight Center in Greenbelt, Md.
The IBEX spacecraft was launched in October 2008. Its science objective is to discover the nature of the interactions between the solar wind and the interstellar medium at the edge of our solar system.
The Southwest Research Institute developed and leads the IBEX mission with a team of national and international partners. The spacecraft is one of NASA’s series of low-cost, rapidly developed missions in the Small Explorers Program. Goddard manages the program for the agency’s Science Mission Directorate at NASA Headquarters in Washington.
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