Signs Changing Fast For Voyager At Solar System Edge

This artist's concept shows NASA's two Voyager spacecraft exploring a turbulent region of space known as the heliosheath, the outer shell of the bubble of charged particles around our sun. 

Image credit: NASA/JPL-Caltech 

For the last seven years, Voyager 1 has been exploring the outer layer of the bubble of charged particles the sun blows around itself. In one day, on July 28, data from Voyager 1's cosmic ray instrument showed the level of high-energy cosmic rays originating from outside our solar system jumped by five percent. During the last half of that same day, the level of lower-energy particles originating from inside our solar system dropped by half. However, in three days, the levels had recovered to near their previous levels.

A third key sign is the direction of the magnetic field, and scientists are eagerly analyzing the data to see whether that has, indeed, changed direction. Scientists expect that all three of these signs will have changed when Voyager 1 has crossed into interstellar space. A preliminary analysis of the latest magnetic field data is expected to be available in the next month.

 

This graphs shows the amount of cosmic rays encountered by the Voyager 1 spacecraft from June 2011 to June 2012 with an increase starting in May 2012. From January 2009 to January 2012, there had been a gradual increase of about 25 percent in the amount of galactic cosmic rays Voyager was encountering. Beginning on May 7, 2012, the cosmic ray hits have increased five percent in a week and nine percent in a month.  This sharp increase in cosmic rays could herald Voyager 1's long-awaited breakthrough to interstellar space. 

Credit: NASA/JPL

"These are thrilling times for the Voyager team as we try to understand the quickening pace of changes as Voyager 1 approaches the edge of interstellar space," said Edward Stone, the Voyager project scientist based at the California Institute of Technology, Pasadena, Calif. "We are certainly in a new region at the edge of the solar system where things are changing rapidly. But we are not yet able to say that Voyager 1 has entered interstellar space."

The levels of high-energy cosmic ray particles have been increasing for years, but more slowly than they are now. The last jump — of five percent — took one week in May. The levels of lower-energy particles from inside our solar system have been slowly decreasing for the last two years. Scientists expect that the lower-energy particles will drop close to zero when Voyager 1 finally crosses into interstellar space.

 

Old vs New Heliopause Model: Old (left) and new (right) views of the heliosheath. Red and blue spirals are the gracefully curving magnetic field lines of orthodox models. New data from Voyager add a magnetic froth (inset, right) to the mix. 

Credit: NASA

"The increase and the decrease are sharper than we've seen before, but that's also what we said about the May data," Stone said. "The data are changing in ways that we didn't expect, but Voyager has always surprised us with new discoveries."

Voyager 1, which launched on Sept. 5, 1977, is 11 billion miles (18 billion kilometers) from the sun. Voyager 2, which launched on Aug. 20, 1977, is close behind, at 9.3 billion miles (15 billion kilometers) from the sun.

 

Heliosphere Diagram: The heliosphere surrounding our solar system is buffeted by strong magnetic fields, shown here as the black, diagonal, upward-pointing arrows. The heliosphere and the interstellar material of the local cloud pass by each other at a speed of 52,000 miles per hour, as shown by the blue arrow. The density of the material and the ramming pressures of the magnetic field coupled with the relatively slow speed of the heliosphere add up to indicate that there is no bow shock at the front of the heliosphere. 

Credit: SWRI

 

"Our two veteran Voyager spacecraft are hale and healthy as they near the 35th anniversary of their launch," said Suzanne Dodd, Voyager project manager based at NASA's Jet Propulsion Laboratory, Pasadena. "We know they will cross into interstellar space. It's just a question of when."

 

Stars travel through the galaxy surrounded by a bubble of charged gas and magnetic fields, rounded at the front and trailing into a long tail behind. The bubble is called an astrosphere, or — in the case of the one around our sun — a heliosphere. This image shows a few examples of astrospheres that are very strong and therefore visible. 

Credit: NASA/GSFC 

The Voyager spacecraft were built by JPL, which continues to operate both. JPL is a division of the California Institute of Technology. The Voyager missions are a part of the NASA Heliophysics System Observatory, sponsored by the Heliophysics Division of the Science Mission Directorate in Washington.

 

 

Contacts and sources:
Jia-Rui Cook 
Jet Propulsion Laboratory, Pasadena, Calif.