  Recently, full sky maps from Planck have been made publicly available. In
this paper, we do consistency tests for the three Planck CMB sky maps. We
assume that the difference between two maps represents the contributions from
systematics, noise, foregrounds and other sources, and that a precise
representation of the Cosmic Microwave Background should be uncorrelated with
it. We investigate the cross correlation in pixel space between the difference
maps and the various Planck maps and find no significant correlations, in
comparison to 10000 random Gaussian simulated maps. Additionally we investigate
the difference map between the WMAP ILC 9 year map and the ILC 7 year map. We
perform cross correlations between this difference map, and the ILC9 and ILC7,
and find significant correlations only for the ILC9, at more than the 99.99%
level. Likewise, a comparison between the Planck NILC map and the WMAP ILC9
map, shows a strong correlation for the ILC9 map with the difference map, also
at more than the 99.99% level. Thus the ILC9 appears to be more contaminated
than the ILC7, which should be taken into consideration when using WMAP maps
for cosmological analyses.
