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Solitary
Waves In Translation
Friday, March 7, 2008
A
soliton in water. The original phenomenon seen in 1834
reproduced on the Scott Russell Aqueduct over the Union
Canal near Heriot-Watt University, UK, 12 July 1995.
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Credits:
Heriot- Watt University (D. Dugald)
Swooping through space are
solitary waves, which in theory do not change form or lose energy
as they go along. These waves, which exist on Earth in different
media, have been detected and explained for the first time in
space thanks to Cluster data.
In theory, these
solitary waves, called solitons, propagate endlessly maintaining
their shape and form as well as velocity, which means that they
do not lose energy with time.
The phenomenon was first
noticed in a water canal in England in 1834 by John Scott Russel,
who named it a ‘wave of translation’. In water,
solitons can be created when a sudden impulse hits the medium and
propagates along it. This is made possible by a delicate balance
of physical parameters that reinforces the wave without
additional energy input externally. Today, optic fibers carry
large amounts of information over very long distances making use
of soliton waves. This provides crystal-clear international phone
calls and fast internet connections.
On 30 March 2002, at
a distance of 50 000 km from Earth, the satellites of the Cluster
constellation detected turbulence in the magnetopause, the outer
boundary of the magnetosphere. Simultaneous measurements by three
of the satellites detected a soliton breaking away from the
turbulent region towards the magnetosphere. The wave traveled for
a long distance and vanished at some point.
“Knowing
the positions and separation of the spacecraft at that time, we
have found that the wave was 6-7 km in size and moved in towards
the magnetosphere at roughly 8 to 9 km/s. We couldn’t have
done this without multiple spacecraft,” said Raoul Trines
of the Rutherford Appleton Laboratory, UK, lead author of the
study.
This phenomenon is very
difficult to study on Earth because the soliton-like structures
that are observed tend to be much smaller in size, similar to the
size of the instruments that are used to probe them. Thus, the
instruments can disturb the phenomenon itself. Given the fact
that the soliton detected in space was very large, the
disturbance caused to the wave as the satellites probed it was
negligible.
The observations performed by the Cluster
satellites were found to be in good agreement with computer
simulations, confirming earlier theoretical predictions of their
existence.
“Thanks to its multiple spacecraft,
Cluster has the unique capability to differentiate spatial
variations from temporal variations. This makes it the first
mission to confirm the theoretical prediction of solitons in
space,” said Philippe Escoubet, ESA’s Cluster and
Double Star Project Scientist. “This result is truly one of
the mission’s scientific highlights,” he added.
Related Article: The
perfect slow wave
Source:
ESA
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