Discovery News / By Irene Klotz

A NASA robotic probe sampling particles flowing into our solar system from the galactic neighborhood shows we're living in a cloud -- and likely to stay that way for hundreds or even thousands of years.

The measurements from NASA's Interstellar Boundary Explorer, or IBEX, spacecraft include the first direct samplings of hydrogen, oxygen and neon that didn't come from the sun or anywhere else in the solar system.

Instead, the gases, along with helium, which was previously detected by NASA's Ulysses spacecraft, streamed into our solar system from the galactic neighborhood, which right now includes a tenuous wispy cloud.

The flow of intergalactic particles is slower than expected, though still zipping along at a hearty 52,000 mph, and coming from a slightly different direction than previously thought.

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That has several implications, including a new assessment that the sun and its brood of planets, asteroids, comets and everything else within the sun's protective, pressurized cocoon -- a structure known as the heliosphere -- is not going to be leaving the cloud that has been our home for the past 45,000 years or so anytime soon.

The slower flow also means that the heliosphere faces less pressure from the outside, making it more susceptible to external magnetic forces. Consequently, it has a different shape than previously thought, more like a squashed beach ball than a speeding bullet.

"The heliosphere is essentially the balance between outward-moving solar wind and the compression from the gas and dust that surround it, so if you're in a different interstellar medium environment, you're going to create a different heliospheric structure," said astronomer Seth Redfield with Wesleyan University.

That in turn impacts how effectively the heliosphere shields the solar system from galactic cosmic rays and other high-energy radiation.

"As the sun moves through space and moves in and out of interstellar clouds, the flux of galactic cosmic rays at the Earth really changes. Someday maybe we'll be able to link the sun's motion through interstellar clouds with the geologic history of Earth. I think that would be really exciting," added University of Chicago senior scientist Priscilla Frisch.

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The new results also raise questions about where the solar system came from. Analysis of the interstellar gases collected by IBEX shows a shortage of oxygen, relative to the amount of neon.

"The local cloud is actually somewhat different in composition than the sun and the Milky Way as a whole, said University of New Hampshire physicist Eberhard Möbius.

"That leaves us with a puzzle for now. Could it be that some of this oxygen is locked up in the cosmic dust? Or does it tell us how different our neighborhood is compared to the sun's birthplace?" he said.

Six papers on the new IBEX findings are published in this week's Astrophysical Journal.