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Almost every day, the great antennas of NASA's Deep Space Network turn to a blank patch of sky in the constellation Ophiuchus. Pointing at nothing, or so it seems, they invariably pick up a signal, faint but full of intelligence. The source is beyond Neptune, beyond Pluto, on the verge of the stars themselves.

It's Voyager 1. The spacecraft left Earth in 1977 on a mission to visit Jupiter and Saturn. Almost 30 years later, with the gas giants long ago seen and done, Voyager 1 is still going and encountering some strange things.

"We've entered a totally new region of space," says Ed Stone, Voyager project scientist and the former director of JPL. "And the spacecraft is beaming back surprising new information."

Before we reveal the surprises, let us discuss exactly where Voyager 1 is:

Our entire solar system-planets and all-sits inside a gargantuan bubble of gas about four times wider than the orbit of Neptune. The sun is responsible. It blows the bubble by means of the solar wind. Astronomers call the bubble itself "the heliosphere" and its outer membrane "the heliosheath."

Voyager 1 is about 10 billion miles from Earth, inside the heliosheath.

see caption"You can simulate the heliosheath in your kitchen sink," says Stone. "Turn on the faucet so that a thin stream of water pours into the sink. Look down into the basin. Where the stream hits bottom, that's the sun. From there, water flows outward in a thin, perfectly radial sheet. That's the solar wind. As the water (or solar wind) expands, it gets thinner and thinner, and it can't push as hard. Abruptly, a sluggish, turbulent ring forms. That ring is the heliosheath."

"The heliosheath is important to humans," continues Stone. "It helps protect us from galactic cosmic rays." Galactic cosmic rays are subatomic particles accelerated to nearly light speed by supernovas and black holes. Astronauts out in space are exposed to the particles-and that's not a good thing. Cosmic rays can penetrate flesh and damage DNA. Fortunately, the heliosheath deflects many cosmic rays before they ever reach the inner solar system. "Magnetic turbulence in the heliosheath scatters the particles harmlessly away."

Note: We have many shields against cosmic rays from the thin walls of spaceships to massive planetary atmospheres. But the heliosheath is our first line of defense, and that makes it special.

Because of its role as Solar System Protector, "we need to learn as much as we can about the heliosheath," says Stone. "Voyager 1 is giving us our first look inside."



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