June 27, 2013:Three new papers published in today's

issue of Science suggest that Voyager 1, now more than 18 billion

kilometers from the sun, is closer to becoming the first human-made

object to reach interstellar space.

"This strange, last region before interstellar space is coming

into focus, thanks to Voyager 1, humankind's most distant scout," said

Ed Stone, Voyager project scientist at the California Institute of

Technology in Pasadena.

Voyager 1 is the near the edge of the heliosphere, a vast bubble

made of the sun's own magnetic field. When Voyager punches through the

bubble, it will exit the solar system and enter interstellar space--the

realm of the stars.

The papers describe how Voyager 1's recent entry into a region called "the magnetic highway"

revealed two of three telltale signs of a breakthrough: charged

particles disappearing as they zoom out along the solar magnetic field,

and cosmic rays from far outside zooming in. Scientists have not yet

seen the third sign, an abrupt change in the direction of the magnetic

field, which would indicate the presence of the interstellar magnetic

field.

"If you looked at the cosmic ray and energetic particle data in

isolation, you might think Voyager had reached interstellar space," says

Stone, "but the team feels Voyager 1 has not yet gotten there because

we are still within the domain of the sun's magnetic field."

Voyager 1 and its twin spacecraft, Voyager 2, were launched in

1977. They toured Jupiter, Saturn, Uranus and Neptune before embarking

on their interstellar mission in 1990. They now aim to leave the

heliosphere. Measuring the size of the heliosphere is part of the

Voyagers' mission.

Voyager 2 is about 9 billion miles (15 billion kilometers) from

the sun and still inside the heliosphere. Voyager 1 was about 11 billion

miles (18 billion kilometers) from the sun Aug. 25 when it reached the

magnetic highway, which appears to connect the spacecraft to

interstellar space. This region allows charged particles to travel into

and out of the heliosphere along a smooth magnetic field line, instead

of bouncing around in all directions as if trapped on local roads.

Voyager 1 can therefore sample interstellar space before it actually

enters the new realm.

Scientists do not know exactly how far Voyager 1 has to go to

reach interstellar space. They estimate it could take several more

months, or even years, to get there. The arrival could come at any time,

so stay tuned.