We report the first direct detection of an exoplanet in the visible polarized light .
The transiting planet HD189733b is one of the very hot Jupiters with shortest periods and , thus , smallest orbits , which makes them ideal candidates for polarimetric detections .
We obtained polarimetric measurements of HD189733 in the B band well distributed over the orbital period and detected two polarization maxima near planetary elongations with a peak amplitude of \sim 2 \cdot 10 ^ { -4 } .
Assuming Rayleigh scattering , we estimated the effective size of the scattering atmosphere ( Lambert sphere ) to be 1.5 \pm 0.2 R _ { J } , which is 30 % larger than the radius of the opaque body previously inferred from transits .
If the scattering matter fills the planetary Roche lobe , the lower limit of the geometrical albedo can be estimated as 0.14 .
The phase dependence of polarization indicates that the planetary orbit is oriented almost in a north-south direction with a longitude of ascending node \Omega = ( 16° or 196° ) \pm 8° .
We obtain independent estimates of the orbit inclination i =98° \pm 8°and eccentricity e =0.0 ( with an uncertainty of 0.05 ) which are in excellent agreement with values determined previously from transits and radial velocities .
Our findings clearly demonstrate the power of polarimetry and open a new dimension in exploring exoplanetary atmospheres even for systems without transits .