  Broadband imaging photometry, and broadband and narrowband linear polarimetry
was 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. The absolute R filter magnitude at zero phase angle is 15.05 +/-
0.05, and corresponds to an equivalent radius for the nucleus of 2.43 +/- 0.06
km (for an adopted albedo of 0.047). The nucleus color V - R is 0.47 +/- 0.07,
suggesting a spectral slope of 11 +/- 8 %/100nm. The phase function of linear
polarimetry in the V and R filters shows a widely color independent linear
increase with phase angle (0.12 +/- 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.
  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.
