Visible light from planet observed orbiting distant star

PORTLAND, Ore. — Scientists have for the first time detected visible light from a planet orbiting a star other than the Sun.

Using a polarization technique, the international team of astronomers led by Svetlana Berdyugina at the Swiss Federal Institute of Technology (ETH, Zurich), tracked the light reflected from the planet through its phases.

The star, called HD189733, is more than 60 light years from Earth in the constellation Vulpecula. The planet was first detected indirectly two years ago by Doppler spectroscopy, but light coming directly from it remained unobserved until the new polarization technique filtered away most of the reflected sunlight. The technique reduced glare, enabling researchers to infer the size and details of the planet's orbit.

Artistic rendering of the HD189733 star-planet system at half-moon phase when polarization of light reflected by the planet reaches its maximum.

The astronomers were also able to determine that the newly observed planet is a gas giant similar to Jupiter. However, it is in an orbit so close to its sun that a gas envelope has developed around the planet that is 30 percent larger than the opaque body of the planet. The planet orbits its sun every two Earth days, according to the scientists; Jupiter that takes 12 Earth years to orbit the Sun.

The atmosphere of the gas giant planet probably consists of particles smaller than half a micron, according to the team, probably made up of tiny dust grains, water vapor or other large atoms or small molecules. The atmosphere scatters light, making it appear blue like the Earth sky.

The scientists were able to track the planet's bluish reflected light through its phases as it circles behind and transits in front of the star. Peak output of reflected light from the planet occurs twice during its orbit at half-phase directly adjacent the star on each side.

The scientists are now trying to measure the radii, mass and density the planet.

They used a 60-cm diameter (nearly two feet) Kungliga Vetenskapsakademien telescope, which is owned by the Royal Swedish Academy of Science (La Palma, Spain). The telescope was upgraded by scientists in Finland and operated remotely by ETH.

Besides Berdyugina, team members included Dominique Fluri of ETH Zurich along with Vilppu Piirola and Andrei Berdyugin from the Tuorla Observatory in Finland.