  We present resolved scattered-light images of the debris disk around HD
107146, a G2 star 28.5 pc from the Sun. This is the first debris disk to be
resolved in scattered light around a solar-type star. We observed it with the
HST/ACS coronagraph, using a 1.8'' occulting spot and the F606W (broad V) and
F814W (broad I) filters. Within 2'' from the star, the image is dominated by
PSF subtraction residuals. Outside this limit, the disk looks featureless
except for a northeast-southwest brightness asymmetry that we attribute to
forward scattering. The disk has scattered-light fractional luminosities of
$(L_{Sca}/L_*)_{F606W}=6.8 \pm 0.8 \times 10^{-5}$ and
$(L_{Sca}/L_*)_{F814W}=10 \pm 1 \times 10^{-5}$ and it is detected up to 6.5''
away from the star. To map the surface density of the disk, we deproject it by
$25^\circ \pm 5^\circ$, divide by the dust scattering phase ($g_{F606W} = 0.3
\pm 0.1$, $g_{F814W} = 0.2 \pm 0.1$) and correct for the geometric dilution of
starlight. Within the errors, the surface density has the same shape in each
bandpass, and it appears to be a broad (85 AU) ring with most of the opacity
concentrated at 130 AU. The ratio of the relative luminosity in F814W to that
in F606W has the constant value of $1.3\pm0.3$, with the error dominated by
uncertainties in the value of $g$ in each filter. An examination of far
infrared and submillimeter measurements suggests the presence of small grains.
The colors and the derived values of $g$ are consistent with the presence of
dust particles smaller than the radiation pressure limit. The dust generated by
the creation of a small planet or the scattering and circularization of a large
one, are possible scenarios that may explain the shape of the surface density
profile.
