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Northern lights glimmer with unexpected trait
April 28, 2008WASHINGTON-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° 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, or 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.
American Geophysical Union
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° 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, or 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.
American Geophysical Union
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Clemson scientists launch rockets to test atmospheric conditions
Clemson University space physicists have traveled around the world to launch rockets to test atmospheric conditions.
Scientists solve 30-year-old aurora borealis mystery
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NASA spacecraft make new discoveries about Northern Lights
A fleet of NASA spacecraft, launched less than eight months ago, has made three important discoveries about spectacular eruptions of Northern Lights called "substorms" and the source of their power.
Unexpected cooling effect in Saturn's upper atmosphere
UK researchers from University College London (UCL), along with colleagues from Boston University, have found that the hotter than expected temperature of Saturn's upper atmosphere - and that of the other giant planets - is not due to the same mechanism that heats the atmosphere around the Earth's Northern Lights.
Northern lights research enters final frontier
An international team of scientists — including physicists from the University of Calgary — will begin gathering the most detailed information yet about the ever-changing northern lights, as a multi-year research project enters its ultimate phase with the launch of five NASA satellites from Cape Canaveral next month.
Chandra looks back at the Earth
In an unusual observation, a team of scientists has scanned the northern polar region of Earth with NASA's Chandra X-ray Observatory.
Hundreds of auroras detected on Mars
Auroras similar to Earth's Northern Lights appear to be common on Mars, according to physicists at the University of California, Berkeley, who have analyzed six years' worth of data from the Mars Global Surveyor.
Movement of Earth's North Magnetic Pole Accelerating Rapidly
After some 400 years of relative stability, Earth's North Magnetic Pole has moved nearly 1,100 kilometers out into the Arctic Ocean during the last century and at its present rate could move from northern Canada to Siberia within the next half-century.
New observations show dynamic particle clumps in Saturn's A ring
New observations from the Cassini spacecraft now at Saturn indicate the particles comprising one of its most prominent rings are trapped in ever-changing clusters of debris that are regularly torn apart and reassembled by gravitational forces from the planet.
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