Probes show solar system dented, not round

WASHINGTON -- When viewed from the rest of the galaxy, the edge of our solar system appears slightly dented as if a giant hand is pushing one edge of it inward, far-traveling NASA probes reveal.

Information from Earth's first space probes to hit the thick edge of the solar system -- called the heliosheath where the solar wind slows abruptly -- paint a picture that is not the simple circle that astronomers long thought, according to several studies published today in the journal Nature. Surprised astronomers said they will have to change their models for what the solar system looks like.

In 1977, NASA launched two space probes on missions beyond the solar system. Voyager 1 went one direction and Voyager 2 went the opposite. What startled astronomers is that when the two of them hit the heliosheath they did so at different distances from the sun.

Voyager 2 hit the edge of the solar system nearly 1 billion miles closer to the sun than Voyager 1 did. Voyager 2 hit the edge at 7.8 billion miles from the sun.

"We used to assume that it's all symmetric and simple," said Leonard Burlaga, an astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md. "It's literally like a hand pushing."

That push is from the magnetic field that lies between star systems in the Milky Way. The magnetic field hits the solar system at a different angle on Voyager 2's side than on Voyager 1's side, probably because of interstellar turbulence from star explosions, said Voyager project scientist Ed Stone.

Both spacecraft still have several more years before they completely exit the solar system and continue deeper into the space between stars, said Stone, former director of NASA's Jet Propulsion Lab.