Context : Short-period comet 2P/Encke is a favorable target for studies of light scattering by bare cometary nuclei .
These studies enable assessment of the nucleus size , the material albedo , and the light-scattering properties of the cometary surface .

Aims : We characterize the activity of the cometary coma and the physical properties of the nucleus of 2P/Encke such as its size , albedo , colors , spectral slope , surface roughness , porosity , and single-particle properties .

Methods : Broadband imaging photometry and broadband and narrowband linear polarimetry is measured for the nucleus of 2P/Encke over the phase-angle range 4 – 28 deg .
An analysis of the point spread function of the comet reveals only weak coma activity , corresponding to a dust production of the order of 0.05 kg/s .
The nucleus displays a color independent photometric phase function of almost linear slope ( \beta = 0.050 \pm 0.004 mag/deg ) .
The absolute R filter magnitude at zero phase angle is 15.05 \pm 0.05 , and corresponds to an equivalent radius for the nucleus of 2.43 \pm 0.06km ( adopted albedo of 0.047 ) .
The nucleus color V - R is 0.47 \pm 0.07 , suggesting a spectral slope S ^ { \prime } of 11 \pm 8 % /100nm .
The phase function of linear polarimetry in the V and R filter shows a widely color independent linear increase with phase angle ( 0.12 \pm 0.02 % /deg ) .
We find discrepancies in the photometric and polarimetric parameters between 2P/Encke and other minor bodies in the solar system , which may indicate significant differences in the surface material properties and light-scattering behavior of the bodies .

Results : The linear polarimetric phase function of 2P/Encke presented here is the first ever measured for a cometary nucleus , and its analysis encourages future studies of cometary nuclei in order to characterize the light-scattering behavior of comets on firm empirical grounds and provide suitable input to a comprehensive modeling of the light scattering by cometary surfaces .

Conclusions :