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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