Over the course of a year, NASA's Interstellar Boundary Explorer (IBEX) scans the entire sky. During February, its instruments are aligned in the correct direction to intercept atoms that have crossed the boundary from interstellar space into our solar system, become caught by the Sun's gravity and slung around the star. This has now allowed IBEX to capture the most complete glimpse of the material that travels in the galactic wind in the space between star systems. The results indicate this material doesn't look like the same material that makes up our solar system.
Our solar system is surrounded by a great magnetic bubble known as the heliosphere. Virtually all of the material in the heliosphere emanates from the Sun, which pumps out solar particles that stream to the edge of the solar system and collide with the material in interstellar space at a boundary called the heliosheath. It is this boundary that IBEX, which is currently in a high-altitude sun-oriented elliptical orbit around the Earth, was tasked with mapping when it was launched in October 2008.
While electrically charged particles traveling through interstellar space on the galactic wind rebound off the heliosheath, neutral particles are able to cross the boundary as if it didn't exist. It is the observation of Energetic neutral atom (ENA) emissions - which are created at the heliosphere by interactions between solar wind particles and interstellar medium particles - by the IBEX and Cassini spacecraft that enabled the first comprehensive sky map of our solar system and its place in the Milky Way galaxy.
Now, NASA says by counting the neutral atoms observed in 2009 and 2010, IBEX has provided clues about how and where our solar system formed, the forces that physically shape our solar system, and even the history of other stars in the Milky Way.
"We've directly measured four separate types of atoms from interstellar space and the composition just doesn't match up with what we see in the solar system," says Eric Christian, mission scientist for IBEX at NASA's Goddard Space Flight Center. "IBEX's observations shed a whole new light on the mysterious zone where the solar system ends and interstellar space begins."
The first direct measurements of hydrogen, helium, oxygen and neon from outside the solar system achieved by IBEX indicate that for every 20 neon atoms in the galactic wind, there are 74 oxygen atoms. However, for every 20 neon atoms in our solar system there are 111 atoms of oxygen. This means that there is more oxygen in any given slice of our solar system than there is in interstellar space.
"Our solar system is different than the space right outside it and that suggests two possibilities," says David McComas the principal investigator for IBEX at the Southwest Research Institute in San Antonio, Texas. "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." Whatever the answer, NASA says the findings affect scientific models of how our solar system - and life - formed.
Additionally, while hydrogen and helium were initially created in the big bang, the heavier elements of oxygen and neon can only be spread through the galaxy by the supernovae explosions at the end of a giant star's life. NASA says knowing the amounts of such elements in space can help map how the galaxy has evolved and changed over time.
IBEX has also been able to measure the pressure exerted on our heliosphere from interstellar material, which will help scientists determine the size and shape of our solar system as it makes its way through the galaxy. The IBEX measurements also indicate that, although researchers had previously theorized that the solar system may lay at the boundary of the local interstellar cloud in which it resides and may be transitioning into a new region of space, we actually remain fully in the cloud - for the time being anyway.
"Sometime in the next hundred to few thousand years, the blink of an eye on the timescales of the galaxy, our heliosphere should leave the local interstellar cloud and encounter a much different galactic environment," McComas says.
A series of papers examining the IBEX findings appeared in The Astrophysics Journal on January 21, 2012.
"This set of papers provide many of the first direct measurements of the interstellar medium around us," says McComas. "We've been trying to understand our galaxy for a long time, and with all of these observations together, we are taking a major step forward in knowing what the local part of the galaxy is like."
Here's a video from NASA explaining the IBEX measurements.
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