Spacecraft captures dust from interstellar wind

Particles giving clues to composition of space beyond solar system

A particle-gobbling probe has snared some alien travelers: tiny particles from interstellar space that, after being born from the ashes of an exploding star, breached a protective bubble blown by the sun and sailed into the jaws of the awaiting spacecraft.

“These are some first observations of interstellar material, really alien matter,” Dave McComas, a principal investigator for NASA’s Interstellar Boundary Explorer spacecraft, or IBEX, said January 31 in a NASA press conference announcing the findings. “This alien interstellar material is really the stuff that stars and planets and people — all of us — are made of,” said McComas, of the Southwest Research Institute in San Antonio.

The spacecraft captured and measured levels of oxygen, hydrogen and neon plucked from puffs of material blown into the solar system. Early analyses of those gases are helping scientists place the solar system in space and define its bubbly shield.
That shield, the heliosphere, is a bubble carved by the sun’s million-mile-an-hour wind. Its edge marks the boundary between the solar system and the surrounding cosmic environment. The turbulent border region repels highly energetic, charged particles, but neutral atoms — like the hydrogen and oxygen IBEX captured — can punch right through.

These are the travelers snared by NASA’s 3-foot-wide spacecraft, in what McComas remarked is like “a 15-billion-mile hole-in-one.”

So far, data from IBEX show that the solar system is still sitting in the “local cloud,” a diffuse, tenuous interstellar puff of gas. Matter spiraling around the Milky Way’s core slips in and out of these low-density clouds, each with a different composition. Scientists think the solar system has been parked in the local cloud for about 45,000 years and will exit within the next few millennia. “How exciting is it that we know where the sun is located now, relative to these interstellar clouds?” asked astronomer Seth Redfield of Wesleyan University in Middletown, Conn., who is not a member of the team.

Studying the particles comprising these clouds yields clues about the context in which stars and planets form — what kinds of protection from high-energy particles and what sorts of elements are needed, Redfield noted. The IBEX results suggest that the cloud the solar system sits in contains considerably less oxygen than does the solar system itself — suggesting either that the solar system formed in an area enriched in oxygen, or that the element is sequestered elsewhere, in things like solid dust grains.

The measurements are “directly telling us about one of the most mysterious elements in our neighborhood of the galaxy, which is oxygen. When we look at the stars we don’t see enough oxygen,” said Priscilla Frisch of the University of Chicago. “So many astronomical questions hinge on issues like that.”

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