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Polarization technique focuses limelight
December 27, 2007An international team of astronomers, led by Professor Svetlana Berdyugina of ETH Zurich's Institute of Astronomy, has for the first time ever been able to detect and monitor the visible light that is scattered in the atmosphere of an exoplanet. Employing techniques similar to how Polaroid sunglasses filter away reflected sunlight to reduce glare, the team of scientists were able to extract polarized light to enhance the faint reflected starlight 'glare' from an 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.
Hot Jupiter
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. HD189733b is so close to its parent star that its atmosphere expands from the heat. Until now, astronomers have never seen light reflected from an exoplanet, although they have deduced from other observations that HD189733b probably resembles a 'hot Jupiter' - a planet orbiting extremely closely to its parent star. Unlike Jupiter, however, HD189733b orbits its star in a couple of days rather than the 12 years it takes Jupiter to make one orbit of the sun.
Two half-moon phases
The international team, consisting of Svetlana Berdyugina, Dominique Fluri (ETH Zurich), Andrei Berdyugin and Vilppu Piirola (Tuorla Observatory, Finland), used the 60cm KVA telescope by remote control. The telescope, which belongs to the Royal Swedish Academy of Science, is located at La Palma, Spain and was modernised by scientists in Finland. The researchers obtained 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 (>30%) 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 sug-gested 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", Pro-fessor Svetlana Berdyugina said. "In addition, more can be learned about radii and true masses, and thus the densities of non-transiting planets."
ETH Zurich/Swiss Federal Institute of Technology
Two half-moon phases
The international team, consisting of Svetlana Berdyugina, Dominique Fluri (ETH Zurich), Andrei Berdyugin and Vilppu Piirola (Tuorla Observatory, Finland), used the 60cm KVA telescope by remote control. The telescope, which belongs to the Royal Swedish Academy of Science, is located at La Palma, Spain and was modernised by scientists in Finland. The researchers obtained 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 (>30%) 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 sug-gested 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", Pro-fessor Svetlana Berdyugina said. "In addition, more can be learned about radii and true masses, and thus the densities of non-transiting planets."
ETH Zurich/Swiss Federal Institute of Technology
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Exoplanet Current Events and Exoplanet News RSSNew technique could find water on Earth-like planets orbiting distant suns
Since the early 1990s astronomers have discovered more than 300 planets orbiting stars other than our sun, nearly all of them gas giants like Jupiter.
Lightest exoplanet yet discovered
Well-known exoplanet researcher Michel Mayor today announced the discovery of the lightest exoplanet found so far. The planet, "e", in the famous system Gliese 581, is only about twice the mass of our Earth.
COROT finds exoplanet orbiting Sun-like star
A team of European scientists working with COROT have discovered an exoplanet orbiting a star slightly more massive than the Sun. After just 555 days in orbit, the mission has now observed more than 50 000 stars and is adding significantly to our knowledge of the fundamental workings of stars.
The Drifting Star
By studying in great detail the 'ringing' of a planet-harbouring star, a team of astronomers using ESO's 3.6-m telescope have shown that it must have drifted away from the metal-rich Hyades cluster. This discovery has implications for theories of star and planet formation, and for the dynamics of our Milky Way.
New rocky planet found in constellation Leo
Spanish and UCL (University College London) scientists have discovered a possible terrestrial-type planet orbiting a star in the constellation of Leo. The new planet, which lies at a distance of 30 light years from the Earth, has a mass five times that of our planet but is the smallest found to date. One full day on the new planet would be equivalent to three weeks on Earth.
COROT surprises a year after launch
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Largest transiting extrasolar planet found around a distant star
An international team of astronomers with the Trans-atlantic Exoplanet Survey announce today the discovery of TrES-4, a new extrasolar planet in the constellation of Hercules.
Massive Transiting Planet with 31-hour Year Found Around Distant Star
An international team of astronomers with the Trans-atlantic Exoplanet Survey today announce the discovery of their third planet, TrES-3.
28 new planets, 7 new brown dwarfs reported by California, Carnegie team
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