Scientists using Voyager 1 data provides new detail of a region where our solar systems heliosphere (the bubble around our Sun and all its planets) and interstellar space connect. Researchers from the Johns Hopkins University Applied Physics Laboratory have discovered a curious and unexpected charged-particle environment – in a region known as the “magnetic highway”. For the first time, scientists can now see the highest level so far of cosmic ray particles from outside the heliosphere coming from our galaxy ‘Milky Way’.
Three papers just published in the journal Science, describe how Voyager 1’s entry into this region called the magnetic highway, resulted in simultaneous observations of the highest rate so far of charged particles from outside heliosphere and the disappearance of charged particles from inside the heliosphere.
Scientists have seen two of the three signs of interstellar arrival they expected to see…charged particles disappearing as they zoom out along the solar magnetic field and cosmic rays from far outside zooming in. Scientists are looking for a third sign – showing an abrupt change in the direction of the magnetic field indicating the presence of the interstellar magnetic field.
The heliosphere extends at least 8 billion miles (13 billion kilometers) beyond all the planets in our solar system. It is dominated by the Sun’s magnetic field and an ionized wind expanding outward from the Sun. Outside the heliosphere, interstellar space is filled with matter from other stars and the magnetic field present in the nearby region of the Milky Way.
Ed Stone, Voyager project scientist at the California Institute of Technology in Pasadena said: “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 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.
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 on Aug. 25th 2012 when it reached the magnetic highway – a connection 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. For the first time in this region, scientists could detect low-energy cosmic rays that originate from dying stars.
Stamatios Krimigis, principal investigator at the Johns Hopkins University Applied Physics Laboratory says: “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. We have never witnessed such a decrease before, except when Voyager 1 exited the giant magnetosphere of Jupiter, some 34 years ago.”
Other charged particle behavior observed by Voyager 1 also indicates the spacecraft still is in a region of transition to the interstellar medium. While crossing into the new region, the charged particles originating from the heliosphere that decreased most quickly were those shooting straightest along solar magnetic field lines. Particles moving perpendicular to the magnetic field did not decrease as quickly. However, cosmic rays moving along the field lines in the magnetic highway region were more intense than those moving vertically to the field. In interstellar space, the direction of the moving charged particles is not expected to matter.In the span of about 24 hours, the magnetic field originating from the Sun also began piling up, like cars backed up on a freeway exit ramp. But scientists were able to quantify that the magnetic field barely changed direction — by no more than 2 degrees.
“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.”