by Richard A. Kerr
A near-infrared image of Cabeus crater, taken from Palomar Observatory after the LCROSS impact today. No ejecta are visible from the image, but further analysis may reveal subtle indications of the crash. (Credit: Palomar Observatory/Caltech)
NASA officials and scientists spent the better part of an hour in this morning's press conference patting themselves on the back. The LCROSS mission in search of lunar water was a great success, they said, all the while ignoring a very large elephant in the room: No one among the millions watching as a 2-ton hunk of metal slammed into the moon could see the much-ballyhooed spray of dust and debris that they had been told to look for.
Even LCROSS scientists have seen nothing of a debris plume. "I'm not necessarily surprised," said LCROSS principal investigator Anthony Colaprete of NASA's
Actually, Colaprete had warned his colleagues, at least, about the possibility of a no-show debris plume. "It's a very unproven and highly unpredictable science, impact cratering," he told an audience at the Lunar and Planetary Science Conference last March. Impact modelers working for the team had struggled to simulate the impact of a cylindrical--not a simpler spherical--object, and one that was hollow, not solid, like the LCROSS impactor. Plus, it smashed into a surface of unknown shape and composition. LCROSS was "the most challenging impact modeling I've ever done," said Erik Asphaug of the
LCROSS scientists may yet extract a debris plume from the data, but "the spectra is where the information is" about any water, Colaprete said, referring to spectral colors in the visible, infrared, and even ultraviolet returned by the trailing LCROSS spacecraft and by the Lunar Reconnaissance Orbiter. Some of these showed intriguing blips from the impact flash and the still-warm crater. There were also spectral changes above the impact site between pre- and postimpact. "What do these little blips mean? I don't know," Colaprete said. "I'm just glad they're there. We're going to work on this feverishly." Even so, no public word about water will be forthcoming before the December meeting of the American Geophysical Union, he said.
Start rooting now for the blips.