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Cluster
and Double Star witness a new facet of Earth’s magnetic
behavior
30 March 2006
Five spacecraft from two
ESA missions unexpectedly found themselves engulfed by waves of
electrical and magnetic energy as they traveled through Earth’s
night-time shadow on 5 August 2004.
The data
collected by the spacecraft are giving scientists an important
clue to the effects of 'space weather' on Earth’s magnetic
field.
Shortly after 15:34 CEST,
something set the tail of Earth’s natural cloak of
magnetism oscillating. "It was like the waves created by a
boat traveling across a lake," says Dr Tielong Zhang of the
Austrian Academy of Sciences, Graz.
Only in this case, the identity
of the 'boat' is unknown. It might be the fast flow of particles
often observed in the central part of the magnetotail. Whatever
it was produced waves that traveled from the center of the tail
to its outer edges.
The five spacecraft caught in
this event were the four units of ESA’s Cluster mission and
the first unit of the joint CNSA/ESA mission Double Star. The
Cluster quartet fly in formation, passing through Earth’s
magnetotail at distances of between 16 and 19 times Earth’s
radius.
One of
the two spacecraft of Double Star, the TC-1 spacecraft, orbits at
between 10 and 13 Earth radii. All five spacecraft are designed
to collect data on the magnetic bubble surrounding our planet,
called the 'magnetosphere'.
Earth’s magnetic field is
generated deep inside the planet and rises into space where it
constantly interacts with the solar wind, a perpetual stream of
electrically charged particles released by the Sun.
The stream pulls Earth’s
magnetic field into a tail that stretches behind the planet for
tens of thousands of kilometers. Gusts and storms in the solar
wind are known as 'space weather' and can make Earth’s
magnetic field quake.
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An
artist's impression of the Cluster quartet
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On 5 August 2004, Cluster
and Double Star satellites found themselves in the right place at
the right time. The readings showed that the oscillations took
place simultaneously across an area over 30 000 km in length.
This is the first time that the true extent of the oscillations
has been revealed.
Previous Cluster measurements,
before the launch of Double Star, could only reveal the movement
across a restricted location surrounded by the four satellites.
Understanding
the way Earth’s magnetic field interacts with the solar
wind is the space-age equivalent of a meteorologist investigating
the way a mountain range disturbs airflow, creating weather
systems.
In the case of space weather,
storms consist of fluctuating magnetic and electrical fields that
can damage satellites and pose health risks to astronauts. If we
are to fully exploit the potential of space, we have to
understand the effects of space weather and be able to predict
them. That’s where missions like Cluster and Double Star
come in.
"By studying the August
oscillations, we may be able to develop a unifying theory for all
the various motions of the magnetotail," says Zhang, who is
heading the investigation into what happened that day.
Source
/ Credit: ESA
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