Voyager 1 News: Probe Now Crossing Where a Mighty Wind Ceases to Blow

Technically, everything within our solar system could be said to exist in the sun's atmosphere.

In most cases we call the corona the sun's upper atmosphere, because that's the part we see as the faint, outermost halo stretching from the bright orb, usually visible from Earth only during a solar eclipse.

(See eclipse pictures from July 2010.)

But the sun's influence stretches farther than that. The star also produces what's known as the solar wind, a flurry of charged particles constantly streaming from the sun in all directions at a whopping 1 million miles (1.6 million kilometers) an hour.

This supersonic wind forms a bubble around our entire solar system called the heliosphere.

But at about 8.7 billion miles (14 billion kilometers) out, the wind speed suddenly drops, creating a warmer, turbulent layer of solar particles around the solar system called the heliosheath.

—Image courtesy NASA/JPL

NASA's Voyager 1 probe, launched in 1977, crossed into the heliosheath in 2004 and began feeding scientists some of the first data on this far-flung region where the solar system meets interstellar space.

Now, scientists announced today, Voyager 1 has reached the part of the heliosheath where the outward speed of the ...