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LCROSS captures all phases of Centaur impact
Posted: October 20, 2009

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Data from the nine LCROSS instruments successfully captured each phase of the impact sequence from impact flash through ejecta plume generation to the formation of a crater, say NASA scientists.

"We are blown away by the data returned," says Anthony Colaprete, LCROSS principal investigator and project scientist. "The team is working hard on the analysis and the data appear to be of very high quality.”

Three co-added LCROSS Visible Light Camera images taken shortly after impact. The extent of the plume at 15 seconds is between six and eight kilometres. Image: NASA.

The LCROSS (Lunar CRater Observation and Sensing Satellite) impacts were designed to throw up potentially icy debris from a permanently shadowed crater at the lunar south pole and comprised the spent Centaur stage of the rocket followed by the Shepherding Spacecraft four minutes later. Instruments on board the Shepherding Spacecraft monitored the Centaur stage impact as it drew progressively closer to the lunar surface. Within the ultraviolet and near infrared spectrometer and camera data is the faint, but distinct, imprint of the debris plume thrown up by the Centaur impact.

"There is a clear indication of a plume of vapor and fine debris," says Colaprete. “Within the range of model predictions we made, the ejecta brightness appears to be at the low end of our predictions and this may be a clue to the properties of the material the Centaur impacted.”

Time series of images collected by the mid-infrared camera (MIR2) from before impact (first two images, the second of which is shown with enhanced contrast stretching), followed by 0, 2, 4 and 6 seconds after impact showing the thermal signature of the impact. Images are in false colour and stretched to enhance contrast. Image: NASA.

The magnitude, form, and visibility of the debris plume, along with thermal data captured by the mid-infrared cameras and emission and absorption spectra across the impact flash, add additional information about the concentrations and state of the material at the impact site.

With the Shepherding Spacecraft returning data right up to the moment it met its demise in the target crater, named Cabeus, it was able to captured detailed images of the Centaur-generated impact crater. At a resolution of less than two metres, early results suggest that the crater is about 28 metres wide.

"The images of the floor of Cabeus are exciting," says Colaprete. "Being able to image the Centaur crater helps us reconstruct the impact process, which in turn helps us understand the observations of the flash and ejecta plume."

The LCROSS team and other observation teams using both Earth- and space-based telescopes will continue to plough through their extensive data sets to provide a complete picture of the impacts and what they mean for the nature and prevalence of materials – perhaps including water ice – at the lunar south pole.