Tuesday, April 29, 2008

Northern Lights Glimmer With Unexpected Trait

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.

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. 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.

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. link
Ref: Polarization in aurorae: A new dimension for space environments studies. 2008. Jean Lilensten et al. GEOPHYSICAL RESEARCH LETTERS, VOL. 35, L08804