  We present an attempt to extract information about the comet 9P/Tempel 1
nucleus from the characteristics of the ejecta cloud produced by the impactor
of the Deep Impact mission. For this purpose we use two techniques. We first
study the shadow cast on the nucleus surface by the ejecta cloud and
investigate how areas of different brightness are related to the varying
optical thickness or albedo of the ejecta cloud. The shadow was seen during the
first 2.0 seconds after the impact (afterward it became obscured by the ejecta
cloud). We have found that all brightness variations in the shadow are the
result of the surface inhomogeneities, indicating that during first 2.0 seconds
the ejecta cloud was homogeneous within the MRI spatial resolution. Our second
technique is to study the obscuration of the nucleus limb by the ejecta. This
study covers the period 0.76- 68.8 seconds after impact and is based on
comparison of the ejecta cloud brightness on the limb and just beyond the limb.
At this stage we do see inhomogeneities in the ejecta cloud that relate to the
albedo and optical thickness variations in the ejected dust. Specifically, we
have found two distinct bands of low optical thickness and one band of a high
optical thickness. Based on crater formation ideas we estimate the depth of
excavation of the ejected material for the found inhomogeneities and, thus,
define a potential layering structure for the comet nucleus, Our estimates
suggest that the low-optical thickness material was excavated from a depth of
15-18 and 30-32 meters in the case the porous nucleus material and 37-46 and
87-93 meters in the case of a non-porous nucleus material, and a layer of high
optical thickness originated from the depth 9-11 m for porous material or 20-23
m for non-porous material. Based on the crater diameter estimates, we expect
that the real depth of the layers is between these two cases.
