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3-D rendition of the Solar System as seen from the outside. It is distorted into bullet shape in the direction of the interstellar magnetic field. The field lines are shown wrapping around the Solar System.
Image: Opher et al. |
ADELAIDE: Our Solar System is unevenly squashed by distortions in the interstellar magnetic field, according to data from the distant Voyager space probes.
Previously, the Solar System was thought to be spherical. But the Voyager II space probe has detected its boundary on one side closer in than Voyager I detected the boundary on the other side, suggesting it is asymmetrical.
"The interstellar magnetic field just outside our Solar System is at a different angle than the magnetic field at very large scales, in the galaxy," said Merav Opher from George Mason University in Fairfax, U.S.
It had previously been thought that the galactic magnetic field was parallel to the plane of our Milky Way galaxy. Now, a study led by Opher and published today in the U.S. journal Science, shows that locally the interstellar magnetic field is at a 60° angle from the galactic plane.
Distorting influence
"The Solar System - the heliosphere - is heavily distorted under the influence of this magnetic field," said Opher.
The heliosphere defines the boundaries of our Solar System, and is made of the solar wind streaming out from the Sun. The solar wind itself comprises magnetic fields and ionised atoms from the Sun's corona travelling at supersonic speeds.
Near the boundary of the Solar System, interstellar wind originating elsewhere in the galaxy collides with the solar wind streaming from the Sun. This produces a 'termination shock' as solar wind particles are slowed to subsonic speeds.
Voyager I, travelling outwards through the northern hemisphere of the solar system, began detecting the termination shock at 85 times the distance between the Earth and the Sun. Voyager II, travelling through the southern hemisphere of the solar system, began detecting this termination shock only 76 times that distance from the Sun, wrote the researchers.
Voyager I set off on September 5, 1977 and hit the termination shock in December 2004. Voyager II, which is travelling more slowly, headed out from Earth on August 20, 1977 and reached the boundary in May 2006.
This suggests that the 'nose' of the heliosphere is being depressed more on the southern side by the interstellar magnetic field. "We are like a bullet-shape bubble inclined in the direction of this magnetic field," said Opher.
Bullet-shaped
Her team used the observations from the Voyager missions to create a 3-D computer model of the heliosphere and the local interstellar magnetic field.
Previously, the direction of the interstellar magnetic field was determined from measurements averaged over large distances – so didn't take into account local, small scale, changes in direction.
Interstellar space is made turbulent and non-uniform from the ancient explosions of stars, said Opher, and this could lead to local distortions of the interstellar magnetic field.
"[This] confirms that the local interstellar magnetic field, which is excluded from the heliosphere, is pointed in a significantly different direction from the larger-scale average field direction," commented space physicist Randy Jokipii at the University of Arizona, in Tucson, U.S..
"This is important for our understanding of the solar system and the Earth's space environment," he said.
