The solar system is travelling through much stormier skies than we thought, and might even be about to pop out of the huge gas cloud we have been gliding through for at least 45,000 years.
That's the implication of a multi-decade survey of the
interstellar wind buffeting the solar system, which has revealed an unexpected
change in the wind's direction.
The edge
of the solar system is roughly defined by the heliosphere,
a giant magnetic bubble blown by charged particles streaming from the sun. This
bubble shields Earth from much of the interstellar wind, so a change in the
wind's direction will have little effect here on the ground.
But the change does
tell us something surprising about our galactic surroundings. The cloud is so
large and diffuse, it was previously assumed to be relatively calm, and that
the wind would blow in the same direction for millions of years.
"If you took a
handful of the air we breathe on Earth and stretched it out to the nearest
star, it would have the same density as this cloud," says Priscilla Frisch of the
University of Chicago.
The fact that the
wind is shifting over the span of mere decades means that the interior of the
cloud is either unusually turbulent, or that the solar system is a mere 1000 or
so years away from punching its way out.
"Think of
looking at clouds in the sky – if you are in that cloud, there's not much
change," says Eberhard
Moebius of the University of New Hampshire in Durham. "But when you
look at the boundary of the cloud, driven around by the wind, you can see fine
structures where it's getting fuzzy and pulled around. We think that this might
be related to these kinds of turbulent structures."
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