Some more notes 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, because:  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 Earth view.  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 background.   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 P.S. - Hubble had a negative spectral detection but are reviewing their results. http://hubblesite.org/newscenter/archive/releases/2009/26/full  "Hubble's Wide Field Camera 3 (WFC3) and Space Telescope Imaging Spectrograph (STIS) were pointed just off the southern limb of the moon to look for a cloud of vaporized material blasted into space by the successive impacts of the rocket booster and spacecraft. The WFC3 images do not show any evidence for a temporary exosphere resulting from the impacts. . . . A preliminary analysis of the STIS spectra do not show any clear evidence for hydroxyl, but further analysis is needed," said Hubble co-investigator Alex Storrs. The Hubble team plans on further analysis of their data." Keck gathered data but is analyzing results. http://keckobservatory.org/index.php/news/a_new_view_of_the_moon