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The solar system has a tail

Clover-shaped clumps of charged particles extend billions of kilometers

The solar system trails a stream of charged particles, as  shown in an illustration. 

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The solar system drags along a lengthy, twisted tail as it moves through the galaxy, researchers announced July 10 in a press conference and in the Astrophysical Journal.

Scientists had always presumed that a tail existed, said Eric Christian, an astronomer at NASA Goddard Space Flight Center in Greenbelt, Md. “But this is the first time we have data that tells us about the tail.”

The discovery comes from data gathered by the Interstellar Boundary Explorer, or IBEX, a satellite launched in 2008. It charts the trajectories of speedy atoms that originate in the outskirts of the solar system before getting an inward kick from collisions with charged particles from the sun. The distribution of those atoms helps scientists map the boundaries of the heliosphere, the bubble that contains the planets and other material in the solar system and is inflated by particles continually jetting out from the sun.

A cross section of the tail resembles a four-leaf clover, with two clumps of slow-moving solar particles and two of high-speed particles. The data also reveal that the clover shape is flattened and twisted by galactic magnetic fields acting on the sun as it whizzes through the Milky Way at around 84,000 kilometers per hour – the same magnetic fields that cause a giant ribbon of charged particles to wrap around the edge of the heliosphere (SN 11/21/09, p. 15).

The IBEX team could not determine the exact length of the tail, said principal investigator David McComas of Southwest Research Institute in San Antonio, but estimated it at 150 billion kilometers, or 1,000 times the distance between Earth and the sun. The team plans to see whether the tail’s shape changes as the sun’s activity wanes.

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