Space

Light Polarization Reveals Exoplanet Characteristics

The search for Earth-like planets

By Gabriel Gache, Science News Editor

27th of December 2007, 11:10 GMT

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Artistic impression of the HD189733 star planet system

While twelve years passed since the first planet that orbits around another star was discovered, we have developed multiple detection techniques such as studying the wobble of the star produced by

the gravitational pull of the planet, or comparing the light emitted from the star in the hope that we might catch the object as it passes in front of its sun. However, the ability to actually study the planet has been mostly reduced to studying the light reflected from the planets atmosphere, or its surface to reveal its chemical composition and size.

To view the surface of an exoplanet through optical methods is highly unpractical as this would require a massive, impossible to build telescope, and light spectroscopy can reveal important information albeit it seem that even this method is insufficient. An international team of astronomers, led by professor Svetlana Berdyugina of ETH Zurich Institute of Astronomy, took the initiative of creating a new method that involves light polarization techniques in order to study light reflected from the atmosphere of the planet.

Light polarization is a characteristic of electromagnetic waves, such as light, and represents the direction of the electric field. Unlike longitudinal waves as the sound, the transverse waves do not exhibit dependency of the oscillating direction in relation to the direction of wave propagation.

The polarization effect is widely used in optical applications which require a reduction in glare or specularity reflections such as the mirror reflections observed on the water surfaces. By doing so, Berdyugina was able to detect for the first time the light dispersed by the atmosphere of another planet, by reducing the starlight brightness and enhancing that coming from the planet.

The exoplanet in question is situated about 60 light years away in the Vulpecula constellation and orbits a white dwarf star known as HD189733. Discovered through light spectroscopy techniques nearly two years ago, HD189733b's orbit take it so close to its star that the heat it receives determines an expansion of the atmosphere, giving the planet a look similar to that of a hot Jupiter.

The planet has an orbit around its star of only a few days, which enables the possibility of making detailed observations when the planet is only half illuminated by its sun, in much the same way the Moon experiences phases. Dispersed light from its atmosphere suggest the presence of particles about half of a micron in diameter, probably atoms and molecules or maybe even water vapor, since it emits a blueish light through the same process responsible for the color of the Earth's sky. In addition to that, the light polarization technique also enabled for the first time the possibility to accurately describe the orbit of an exoplanet.

TAGS:

exoplanet | Earth-like | star | solar system | universe

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