Frank and Sigwarth [1997a] claim that the dark pixels observed in dayg
low images obtained by the Earth sensor of the Visible Imaging System
(VIS) are due to bombardment of Earth by 20 to 40 ton cosmic snowballs
. We have independently studied the VIS data and compared the dark pix
els from the VIS images to those obtained from the overlapping images
from the Ultraviolet Imager (UVI). We find the occurrence distribution
s of the dark pixels, single and multiple, from VIS and UVI are nearly
identical. The distributions also do not show any altitude dependence
. A search for evidence of spacecraft ''wobble'' motion, whose presenc
e would indicate that the source is external to the camera, has found
that pairs of dark pixel clusters are uniformly distributed in orienta
tion and no preference is observed in the wobble direction. Instrument
artifacts as the source of the dark pixels is the most likely explana
tion for these results. The conclusion of this study is that neither V
IS nor UVI provide any scientific evidence that the dark pixels are ge
ophysical.