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Like a comet, our solar system has a tail.
It has never actually been observed. Until now. NASA's
Interstellar Boundary Explorer, or IBEX recently mapped the boundaries
of the solar system's tail, called the heliotail. By combining
observations from the first three years of IBEX imagery, scientists have mapped
out a tail that shows a combination of fast and slow moving
particles. IBEX can map such regions because it uses a technique called energetic
neutral atom imaging. An energetic charged particle
in the outer heliosphere hits a hydrogen atom, stealing its electron
and becoming neutral. It then travels straight, though some of them come back
toward the inner heliosphere. They're they collide with IBEX, and are
detected. By plotting out such neutral atoms and where they came from,
IBEX has recently been able to describe the tail streaming behind the solar
system. The tail is composed of solar wind plasma and magnetic
field. The solar wind streams out from the sun in all directions, out
past the farthest planets. It eventually slows down,
bending back along the tail, due to pressure from the interstellar gas and magnetic
field. Based on the map of the heliotail, if we could look straight
down the tail, we would see a shape a little like a four-leaf clover.
The two side leaves are filled with slow moving particles, and the
upper and lower leaves with fast ones. This is in line with how
the sun releases fast solar wind near its poles, and slower wind
near its equator. The four-leaf clover does not align perfectly with
the solar system. The entire shape is rotated slightly.
This indicates that as it moves farther away from the sun's magnetic influence
the charge particles have begun to be pulled into a new orientation,
aligning with the magentic field of the local galaxy.
Scientists still do not know how long the tail is, but think that it
eventually fades away and becomes indistinguishable from the rest of
interstellar space. Together, data from instruments in space
and analysis at labs on the ground will continue to improve our understanding
of the comet-like tails streaming out behind us.
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