  We investigate the implications for the Planck Surveyor of the recent
sub-millimetre number counts obtained using the SCUBA camera. Since it observes
at the same frequency as one of the higher frequency science channels on
Planck, SCUBA can provide constraints on the point-source contribution to the
CMB angular power spectrum, which require no extrapolation in frequency. We
have calculated the two-point function of these sub-millimetre sources, using a
Poisson model normalized to the observed counts. While the current data are
uncertain, under reasonable assumptions the point-source contribution to the
anisotropy is comparable to the noise in the 353GHz channel. The clustering of
these sources is currently unknown, however if they cluster like the z~3
Lyman-break galaxies their signal would be larger than the primary anisotropy
signal on scales smaller than about 10 arcmin. We expect the intensity of these
sources to decrease for wavelengths longward of 850 microns. At the next lowest
Planck frequency, 217GHz, the contribution from both the clustered and Poisson
terms are dramatically reduced. Hence we do not expect these sources to
seriously affect Planck's main science goal, the determination of the
primordial anisotropy power spectrum. Rather, the potential determination of
the distribution of sub-mm sources is a further piece of cosmology that Planck
may be able to tackle.
