Voyager 1 Still Within The Confines Of Solar System
June 27, 2013

Voyager 1 Still Within The Confines Of Solar System

Lee Rannals for - Your Universe Online

Scientists are split on exactly where NASA's Voyager 1 spacecraft is sitting within the Solar System, but new research from the space agency suggests it is on the last frontier out.

A team of scientists wrote in Geophysical Research Letters in March that the spacecraft had already left our Solar System. However, the latest intel from NASA shows that the spacecraft is still sitting just within the edge of our "Solar Bubble."

Researchers published in the journal Science on Thursday new details on the last region the spacecraft will cross before it leaves the heliosphere, or the bubble around our sun, and enters interstellar space.

Scientists have seen two of the three signs expected to see once Voyager 1 crosses that boundary between our neighborhood and interstellar space. Voyager 1 has seen charged particles disappearing as they zoom out along the solar magnetic field, and cosmic rays from far outside zooming in. However, scientists haven't witnessed the third sign, which is an abrupt change in the direction of the magnetic field, indicating the presence of the interstellar magnetic field.

"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 Caltech in Pasadena, California. "If you looked at the cosmic ray and energetic particle data in isolation, you might think Voyager had reached interstellar space, but the team feels Voyager 1 has not yet gotten there because we are still within the domain of the sun's magnetic field."

Scientists do not know the precise distance Voyager 1 has to go in order to reach interstellar space, but they estimate it could take several more months, or even years, before it leaves the Solar System behind for good. The heliosphere extends at least eight billion miles beyond all the planets in our Solar System. This region is dominated by the sun's magnetic field and an ionized wind expanding outward from the sun. Outside this region, Voyager 1 will run into matter from other stars and the magnetic field present in the nearby region of the Milky Way.

In August of last year, Voyager 1 was about 11 billion miles from the sun and was reported then that it was about to cross the threshold into interstellar space. NASA said this is the point when the spacecraft reached the magnetic highway, or an area known as the depletion region. This region allows charged particles to travel into and out of the heliosphere along a smooth magnetic field line.

"We saw a dramatic and rapid disappearance of the solar-originating particles. They decreased in intensity by more than 1,000 times, as if there was a huge vacuum pump at the entrance ramp onto the magnetic highway," said Stamatios Krimigis, the low-energy charged particle instrument's principal investigator at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. "We have never witnessed such a decrease before, except when Voyager 1 exited the giant magnetosphere of Jupiter, some 34 years ago."

Voyager 1 has also experienced other charged particle behavior indicating the spacecraft is still in a region of transition to the interstellar medium. Cosmic rays moving along the field lines in the magnetic highway region were somewhat more populous than those moving perpendicular to the field.

NASA said in the span of 24 hours, the magnetic field originating from the sun began piling up, like cars backed up on a freeway exit ramp. Scientists were able to quantify that the magnetic field barely changed direction.

"A day made such a difference in this region with the magnetic field suddenly doubling and becoming extraordinarily smooth," said Leonard Burlaga, the lead author of one of the papers, and based at NASA's Goddard Space Flight Center in Greenbelt, Md. "But since there was no significant change in the magnetic field direction, we're still observing the field lines originating at the sun."