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Sun moving slower than expected -- and without bow shock

May 11, 2012|By Thomas H. Maugh II
  • Many stars have bow shock waves, as seen in these images.
Many stars have bow shock waves, as seen in these images. (NASA / ESA / JPL-Caltech…)

The sun and its solar system are moving through the universe significantly more slowly than astronomers had previously believed, too slowly to generate the bow shock wave that researchers had thought preceded it.

The bow shock wave, much like the sonic boom that accompanies an aircraft traveling at supersonic speeds, occurs when particles in gas clouds cannot get out of the way fast enough, and has been routinely demonstrated in images of other stars. But the Earth is traveling slowly enough that its passage through gas clouds is more like the wave that accompanies a subsonic plane or an ocean liner at sea.

The bow shock is thought to help protect Earth from cosmic rays that would be encountered in the interstellar medium and produced as the solar system speeds through the universe.

Its absence could mean that increased penetration of charged particles, which can damage DNA and lead to mutations, could have occurred frequently in the past as the sun passed through interstellar gas clouds, possibly boosting evolution or perhaps even causing extinctions.

The new information was obtained using NASA's orbiting Interstellar Boundary Explorer, or IBEX, and published Friday in the journal Science.

IBEX, launched in 2008, measures the speed of helium atoms impinging on the heliosphere, the bubble of ionized particles emitted by the sun and surrounding the entire solar system to a distance of billions of miles from the star. The electrically neutral helium can pass readily through the heliopause, allowing researchers to directly measure the sun's speed.

Astronomer David McComas of the Southwest Research Institute in San Antonio, Texas, the principal investigator of the IBEX mission, and his colleagues reported in Science that the new data indicates that the sun and Earth are moving through the universe at about 52,000 mph, about 7,000 mph slower than previously thought.

Given the density of the heliosphere, that is not fast enough to generate a bow shock wave, they said. Independent modeling conducted previously had suggested a similar speed, but some astronomers were skeptical. The new results seem to confirm those calculations.

"It's too early to say exactly what this new data mean for our heliosphere," McComas said. "Decades of research have explored scenarios that included a bow shock. That research now has to be redone using the latest data. Already we know there are likely implications for how galactic cosmic rays propagate around and enter the solar system, which is relevant for human space travel."

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