Astronomers detect visible light in exoplanet's atmosphere for first time

The transiting exoplanet under study circles the dwarf star HD189733 in the constellation Vulpecula, and lies more than 60 light years from the earth.

Known as HD189733b, this exoplanet was discovered two years ago via Doppler spec-troscopy. It is so close to its parent star that its atmosphere expands from the heat.

For observing the visible light in the atmosphere of the planet, the research team employed techniques similar to how Polaroid sunglasses filter away reflected sunlight to reduce glare. Using this method, they were able to extract polarized light to enhance the faint reflected starlight 'glare' from the exoplanet.

As a result, the scientists could infer the size of its swollen atmosphere. They also directly traced the orbit of the planet, a feat of visualization not possible using indirect methods.

The international team of astronomers, led by Professor Svetlana Berdyugina of ETH Zurich's Institute of Astronomy, used the 60cm KVA telescope for obtaining the polarimetric measurements of the star and its planet.

They discovered that polarization peaks near the moments when half of the planet is illuminated by the star as seen from the earth. Such events occur twice during the orbit, similar to half-moon phases.

The polarization indicates that the scattering atmosphere is considerably larger than the opaque body of the planet seen during transits, and most probably consists of particles smaller than half a micron, for example atoms, molecules, tiny dust grains or perhaps water vapour, which was recently suggested to be present in the atmosphere.

Such particles effectively scatter blue light - in exactly the same scattering process that creates the blue sky of the earth's atmosphere.

The scientists were also able for the first time to recover the orientation of the planet's orbit and trace its motion in the sky.

"The polarimetric detection of the reflected light from exoplanets opens new and vast opportunities for exploring physical conditions in their atmospheres", said Professor Svetlana Berdyugina. "In addition, more can be learned about radii and true masses, and thus the densities of non-transiting planets," she added. (ANI)

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