From: LARRY KLAES (ljk4_at_msn.com)
Date: Thu Apr 24 2008 - 13:48:08 PDT
>From: "AAS Press Officer Dr. Steve Maran" <steve.maran_at_aas.org>
>To: "Steve Maran" <steve.maran_at_aas.org>
>Subject: AGU: Northern lights glimmer with unexpected trait
>Date: Thu, 24 Apr 2008 16:27:15 -0400
>
THE FOLLOWING RELEASE WAS RECEIVED FROM THE AMERICAN GEOPHYSICAL
UNION, IN WASHINGTON, DC, AND IS FORWARDED FOR YOUR INFORMATION.
(FORWARDING DOES NOT IMPLY ENDORSEMENT BY THE AMERICAN ASTRONOMICAL
SOCIETY.) Steve Maran, American Astronomical Society
steve.maran_at_aas.org 1-202-328-2010 x116
American Geophysical Union - Observatoire des Sciences de l'Univers de
Grenoble Joint Release
24 April 2008
AGU Release No. 08-14
For Immediate Release
Northern lights glimmer with unexpected trait
AGU Contact: Peter Weiss
+1 (202) 777-7507
pweiss_at_agu.org
OSUG Contact:
Syhem Perriot
+33 (0) 4 76 63 55 11
syhem.perriot_at_obs.ujf-grenoble.fr
WASHINGTON -- An international team of scientists has detected that some of
the glow of Earth's aurora is polarized, an unexpected state for such
emissions.
Measurements of this newfound polarization in the Northern Lights may
provide
scientists with fresh insights into the composition of Earth's upper
atmosphere,
the
configuration of its magnetic field, and the energies of particles
from the Sun,
the
researchers say.
If observed on other planets, the phenomenon might also give clues to the
shape
of the Sun's magnetic field as it curls around other bodies in the
solar system.
When a beam of light is polarized, its electromagnetic waves share a common
orientation, say, aligned vertically, or at some other angle. Until now,
scientists
thought that light from energized atoms and molecules in planetary upper
atmospheres could not be polarized. The reason is simple: In spite of the
low
number of particles at the altitudes concerned (above 100 kilometers
(60 miles)), there are still numerous collisions between molecules
and gas atoms. Those collisions depolarize the emitted light.
Fifty years ago, an Australian researcher, Robert Duncan, claimed to observe
what
looked like polarization of auroral light, but other scientists found that
single
observation unconvincing.
To revisit the question, Jean Lilensten of the Laboratory of Planetology of
Grenoble, France, and his colleagues studied auroral light with a
custom-made
telescope during the winters of 2006-2007 and 2007-2008. They made their
observations from Svalbard Island, Norway, which is in the polar region, at
a
latitude of 79 degrees north.
At the north and south magnetic poles, many charged particles in the
solar wind--a
flow of electrically charged matter from the Sun--are captured by the
planet's
field
and forced to plunge into the atmosphere. The particles strike atmospheric
gases,
causing light emissions.
Lilensten and his colleagues observed weak polarization of a red glow that
radiates at
an altitude of 220 kilometers (140 miles). The glow results from electrons
hitting oxygen
atoms. The scientists had suspected that such light might be polarized
because
Earth's magnetic
field at high latitudes funnels the electrons, aligning the angles at
which they
penetrate
the atmosphere.
The finding of auroral polarization "opens a new field in planetology," says
Lilensten, who is the lead author of the study. He and his colleagues
reported
their results on 19 April in Geophysical Research Letters, a publication of
the
American Geophysical Union (AGU).
Fluctuations in the polarization measurements can reveal the energy of the
particles coming from the Sun when they enter Earth's atmosphere, Lilensten
notes. The intensity of the polarization gives clues to the composition of
the
upper
atmosphere, particularly with regard to atomic oxygen.
Because polarization is strongest when the telescope points perpendicularly
to
the
magnetic field lines, the measurements also provide a way to determine
magnetic
field configurations, Lilensten adds. That could prove especially useful as
astronomers train their telescopes on other planetary atmospheres. If
polarized
emissions are observed there as well, the measurements may enable scientists
to
understand how the Sun's magnetic field is distorted by obstacles such as
the
planets Venus and Mars, which lack intrinsic magnetic fields.
**********
Notes for Journalists
Journalists and public information officers of educational and scientific
institutions who have registered with AGU can download a PDF copy of this
paper by clicking on this link:
http://dx.doi.org/10.1029/2007GL033006
If you need instructions for downloading, please see:
http://www.agu.org/jinstructions.shtml
Or, you may order a copy of the paper by emailing your request to
Peter Weiss at
pweiss_at_agu.org. Please provide your name, the name of your publication, and
your phone number.
Neither the paper nor this press release are under embargo.
Title:
"Polarization in aurorae: A new dimension for space environments studies"
Authors:
Jean Lilensten, Mathieu Barthelemy, Roland Thissen, Cyril Simon, Odile
Dutuit:
CNRS-UJF, Laboratoire de Planetologie de Grenoble, Batiment D de physique,
Grenoble, France; Cyril Simon is also at ESTEC, Noordwijk, Netherlands;
Joran Moen: Department of Physics, University of Oslo, Blindern, Oslo,
Norway,
and ESTEC, Noordwijk, Netherlands;
Dag A. Lorentzen, Fred Sigernes: Arctic Geophysics, University Centre in
Svalbard, Longyearbyen, Svalbard, Norway;
Pierre Olivier Amblard: CNRS-INPG, GIPSA Lab, BP 46, Saint Martin d'Heres,
France.
Citation:
Lilensten, J., J. Moen, M. Barthelemy, R. Thissen, C. Simon, D. A.
Lorentzen, O.
Dutuit, P. O. Amblard, and F. Sigernes (2008), Polarization in aurorae: A
new
dimension for space environments studies, Geophys. Res. Lett., 35, L08804,
doi:10.1029/2007GL033006.
Contact information for coauthors:
Jean Lilensten: office: +33 (0) 4 76 51 41 49, email:
jean.lilensten_at_obs.ujf-
grenoble.fr
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