Ditto to Michelle's comments on the mystery of the plumeless crater
Over the next month, the LCROSS team will reconstruct the event in
more detail. The plume failure will turn out to be more of a p.r.
problem than a loss of science information problem. (The p.r. problem
is that the general public was expecting a plume and they are
stakeholders as the financiers of this and future NASA missions.)
Part of the LCROSS team event science reconstruction probably will
address the lack of observable plume.
So, how do you dig a 1 meter deep by 20 meter diameter crater (about
the size of a house foundation), excavate between 200 and 350 metric
tons of dirt and not have a plume? What we do know is that the impact
crater appears to be right-predicted size but no plume was observed. A
top 10 list of possible causes for a "good" crater but no plume are:
1) The plume was there at expected density and was just to faint,
a) The sunlight-topography model was wrong and the curtain never
reached the sunlight.
b) The impacter hit a slope and the ejecta angle sprayed most of the
mass on the back of M1.
c) The impacter hit a boulder in a boulder field and broke up just
before hitting the surface.
d) The topography model was wrong and the plume was blocked from
e) The unknown site specific surface material was compressed rock,
not regolith (the rock ledge theory).
g) (My speculative contribution) They hit a thinly buried ice shelf
and most of the ejecta was in the form of gas (the ice ledge theory).
2) The plume was not there or was only a faint, less-dense-than
predicted curtain, because:
a) The plume model was wrong - the plume was much less dense than
modeled. Basic physics principles for optics controlled the plume's
visiblity. If it was less bright than the "black" shadow region, even
Palomar's 200 inch cannot take an image of the plume that is fainter
than the shadowed portion of the crater against which was the
b) The plume model was right but the surface materials were not
what was anticipated. Same as 1(b)(c) and (d).
The science review with the additional LRO imagery probably will
address and answer these questions.
Clear skies - Kurt
On Oct 10, 7:23 am, "Michelle Nichols" <mnich...@adlerplanetarium.org