NASA Finds Evidence of Plume from Lunar Probes

NASA is calling last week's bombing of the moon a smashing success with the two probes that smacked into the lunar surface Oct. 9 returning tantalizing data, including faint traces of an impact plume. NASA has said it ultimately hopes the probes will yield data about the possibility of water on the moon.

NASA launched an Atlas V rocket to the moon June 18 with two satellites riding on top: the LRO (Lunar Reconnaissance Orbiter) and the LCROSS (Lunar Crater Observation and Sensing Satellite). The LRO is in orbit 31 miles above the moon's surface, mapping the moon in high resolution for future landing sites and gathering crucial data on the lunar environment that will help astronauts prepare for long-duration lunar expeditions.

NASA dropped the LCROSS with the empty 2.5 ton Centaur upper stage of the Atlas rocket still attached out of orbit late Oct. 8 and begin angling for the lunar surface. The Centaur hit the surface first, closely followed by the LCROSS.

What was puzzling, though, was the apparent lack of a debris plume from the twin impacts. NASA had predicted that a 6-mile-high plume of dirt and dust would be created by the impact. But the lack of a plume disappointed a worldwide audience watching on NASA TV and the Internet. NASA's live feed tracked the rapidly descending LCROSS to just before impact and nothing more. The live feed turned to static. Reports from virtually every available Earth- and space-based telescope failed to show either an impact flash or a plume.

But a week later, Anthony Colaprete, LCROSS principal investigator and project scientist, said in an Oct. 16 statement: "There is a clear indication of a plume of vapor and fine debris. 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."

Colaprete also said, "We are blown away by the data returned. The team is working hard on the analysis and the data appear to be of very high quality."

NASA said in the statement:

"The magnitude, form and visibility of the debris plume add additional information about the concentrations and state of the material at the [Cabeus crater] impact site.

"The LCROSS spacecraft also captured the Centaur impact flash in both mid-infrared (MIR) thermal cameras over a couple of seconds. The temperature of the flash provides valuable information about the composition of the material at the impact site. LCROSS also captured emissions and absorption spectra across the flash using an ultraviolet/visible spectrometer. Different materials release or absorb energy at specific wavelengths that are measurable by the spectrometers."

"The images of the floor of Cabeus are exciting," Colaprete said. "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."

NASA also posted some initial images of the impacts on the LCROSS site.