Image courtesy Nathan Schwadron, University of New Hampshire
Published April 7, 2011
The finding is based on newly released data from the Interstellar Boundary Explorer satellite (IBEX), an Earth-orbiting probe that has been mapping the solar system's outer frontier since 2008.
As the sun travels through the galaxy, the solar wind—actually charged particles streaming from the sun—collides with interstellar gases, forming a cocoon around the solar system called the heliosphere.
The edge of this cocoon, the heliopause, lies more than 9 billion miles (14.5 billion kilometers) from the sun.
"The Voyager spacecrafts were the first to reach these outer boundaries, and [they] gave us very localized information," said study leader Nathan Schwadron of the University of New Hampshire. (See "Solar System Is 'Bullet Shaped.'")
"But IBEX now allows us to pull back and finally show us its global properties. We are now overturning 40 years of theories about this gigantic bubble which surrounds and protects our solar system from harmful galactic cosmic rays," high-energy particles that zip through the universe. (Related picture: "Cosmic Ray Mystery Solved?")
Cosmic rays constantly bombard our solar system, but the heliosphere shields us from most of the radiation. Still, the small amounts that leak through and reach Earth can fry satellite electronics and pose a health hazard for astronauts.
Sun Aimed at Cosmic Scorpion
In 2009 IBEX revealed a vast ribbon of atoms snaking its way along the solar system's edge. While intriguing, this ribbon was preventing astronomers from mapping the entire heliosphere.
Now Schwadron and his team have finally been able to digitally subtract the intense emissions given off by this mysterious ribbon, revealing the heliosphere's nose. This feature, like the bow of a ship, appears at the leading edge of the windsock-like heliosphere.
"It turns out that the ribbon happens to go right through this region of the heliosphere, so we just had to pull back that curtain to reveal its signal," Schwadron said.
This nose appears to point in the general direction of the zodiacal constellation Scorpius. From our perspective, Scorpius follows the ecliptic, or the path of Earth's orbit around the sun. Scorpius rises during the summer months in the Northern Hemisphere.
The study authors are still puzzling out what this—and other IBEX data—tells us about the sun's overall trajectory. But it looks like the sun may be following a short, wavelike path that takes it above and below the galactic plane a few times during each orbit around the galaxy's center.
Overall, Schwadron believes IBEX's discoveries will boost our understanding of the heliosphere. For instance, this bubble can inflate and deflate with changes in solar activity and the pressure of interstellar gases—which may have implications for life on Earth and human space exploration.
"What we can start asking now is, how does this boundary essentially protect Earth from the harsh galactic cosmic radiation?" Schwadron said.
"In essence, we could be discovering the domain of habitability within our own heliosphere and even apply that understanding to other planetary systems."
The new IBEX data are described in a paper published online March 23 by the Astrophysical Journal.
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