  We report results from broadband visible images of comet C/2012 S1 (ISON)
obtained with the Hubble Space Telescope Wide Field Camera 3 on 2013 April 10.
C/ISON's coma brightness follows a 1/{\rho} (where {\rho} is the projected
distance from the nucleus) profile out to 5000 km, consistent with a constant
speed dust outflow model. The turnaround distance in the sunward direction
suggests that the dust coma is composed of sub-micron-sized particles emitted
at speeds of tens of meters s$^{-1}$. A({\theta})f{\rho}, which is commonly
used to characterize the dust production rate, was 1340 and 1240 cm in the
F606W and F438W filters, respectively, in apertures <1.6" in radius. The dust
colors are slightly redder than solar, with a slope of 5.0$\pm$0.2% per 100 nm,
increasing to >10% per 100 nm 10,000 km down the tail. The colors are similar
to those of comet C/1995 O1 (Hale-Bopp) and other long-period comets, but
somewhat bluer than typical values for short-period comets. The spatial color
variations are also reminiscent of C/Hale-Bopp. A sunward jet is visible in
enhanced images, curving to the north and then tailward in the outer coma. The
1.6"-long jet is centered at a position angle of 291$^\circ$, with an opening
angle of about 45$^\circ$. The jet morphology remains unchanged over 19 hours
of our observations, suggesting that it is near the rotational pole of the
nucleus, and implying that the pole points to within 30 deg of (RA, Dec) =
(330$^\circ$, 0$^\circ$). This pole orientation indicates a high obliquity of
50$^\circ$-80$^\circ$.
