Moving to the rhythm of the Sun (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Thu, 23 Aug 2007 04:24:50 GMT
ESA News
http://www.esa.int
17 August 2007
Moving to the rhythm of the Sun
Scientists from the Ulysses mission have proven that sounds generated deep
inside the Sun cause the Earth to shake and vibrate in sympathy. They have
found that Earth's magnetic field, atmosphere and terrestrial systems, all
take part in this cosmic sing-along.
David Thomson and Louis Lanzerotti are team members of the HISCALE
experiment on board Ulysses, a joint mission between ESA and NASA.
Together with colleagues Frank Vernon, Marc Lessard and Lindsay Smith,
they present evidence that proves that Earth moves to the rhythm of the
Sun. They show that distinct, isolated tones, predicted to be generated by
pressure and gravity waves in the Sun, manage to reach Earth and are
detectable in our environment.
Using highly sophisticated statistical techniques, Thomson and colleagues
have discovered these same, distinct tones emitted by the Sun, in seismic
data here on Earth. They have also found that Earth's magnetic field and
atmosphere, and even voltages induced on ocean cables, are all taking part
in this cosmic sing-along.
Although these tones are all around us, it would not be possible for us to
hear them, even if we listened very closely. Their pitch is too low for
the human ear, typically 100-5000 microHertz (1 microHertz corresponds to
1 vibration every 278 hours). This is more than 12 octaves below the
lowest note audible to humans. For comparison, the note to which
orchestras tune their instruments (A above Middle C on a piano)
corresponds to 440 Hertz.
According to Thomson, data from Ulysses provided an important clue as to
how these sounds generated deep inside the Sun reach the Earth.
The same techniques applied to the terrestrial data sets were first used
on measurements of energetic particle fluxes and interplanetary magnetic
fields recorded on board Ulysses.
Surprisingly, rather than being random in nature, the fluctuations in the
data were made up of many discrete frequencies or tones, similar to the
terrestrial data. These tones also corresponded well to those that
theorists predict, should be generated by pressure and gravity waves in
the Sun.
Some of these so-called solar oscillations had been observed optically
using instruments on SOHO, and by dedicated networks of telescopes on the
Earth. They are caused by pressure waves in the Sun, and are referred to
as p-modes. The deeper sounds associated with the Sun's gravity waves
(g-modes) are far more elusive.
Just as seismologists on Earth use sound waves to probe the interior of
our world, solar scientists would like to use g-modes to probe the core of
the Sun, if only they could detect them. G-modes have been undetectable
optically, so Thomson and colleagues' evidence for them in interplanetary
data was both unexpected and hard to explain at first.
They examined a wide range of data sets covering natural phenomena and
technological systems in fields as diverse as telecommunications and
seismology and continued to find new evidence of discrete tones with
characteristics of solar oscillations in what was previously considered
background "noise". This added to the puzzle posed by the Ulysses
findings.
Thomson believes that the key to the problem is magnetism. He suggests
that the g-mode vibrations are picked up by the magnetic field at the
Sun's surface. Part of this magnetic field is then carried away from Sun
into interplanetary space by solar wind, where it can be detected by space
probes like Ulysses.
The magnetic field of the solar wind in turn interacts with the Earth's
magnetic field and causes it to vibrate in sympathy, retaining the
characteristic g-mode signals. The motions of the geomagnetic field then
couple into the solid Earth to produce small, but easily detectable,
responses as Earth, with many of its technological systems, moves to the
rhythm of the Sun.
Notes for editors:
Ulysses is a joint mission between ESA and NASA.
ESA manages the mission operations and provided the spacecraft, built by
Dornier Systems, Germany (now Astrium). NASA provided the Space Shuttle
Discovery for launch and the inertial upper stage and payload-assist
module to put Ulysses in its correct orbit. NASA also provided the
radioisotope thermoelectric generator which powers the spacecraft and
payload.
ESA's ESTEC and ESOC are now managing the mission with NASA's Jet
Propulsion Laboratory (JPL). Ulysses is tracked by NASA's Deep Space
Network. A joint ESA/NASA team at JPL is overseeing spacecraft operations
and data management. Teams from universities and research institutes in
Europe and the United States provided the nine science instruments.
For more information:
Richard Marsden, ESA Ulysses Project Scientist
Email: richard.marsden @ esa.int
[NOTE: Images supporting this release are available at
http://www.esa.int/esaCP/SEMVA0VL05F_index_1.html ]
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