Bombing the Moon: Spectacularly Unspectacular

The sizzle turned to fizzle for NASA Oct. 9 as it slammed two probes traveling more than 5,000 miles per hour into the moon’s surface in a search for lunar water. While jubilant NASA scientists called the precision strike a success, they are initially puzzled about what happened to an expected 6-mile-high plume of dirt and dust expected to be created by the impact.
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-based and space-based telescope failed to show either an impact flash or a plume.
“At first glimpse there was an impact, we saw the crater and we got the measurements we needed,” LCROSS principal investigator Tony Colaprete said at a NASA press conference 2 hours after the crash. “The impact flash confirmed the actual size of the crater, which was pretty close to what we expected.”
Colaprete stressed all the data and all the images were strictly preliminary. He said the plume could be affected by the angle of the impact, the type of material hit, the composition of the lunar surface and how deep LCROSS buried itself on impact.

He added that NASA scientists were less interested in images than data collected from spectrographs mounted aboard the LCROSS. “I saw variations in the spectra,” Colaprete said. “I’m thrilled-that’s a very good sign. The spectra is where the science is.”

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. 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 two-and-a-half ton Centaur upper stage of the Atlas rocket still attached out of orbit late Oct. 8 to begin angling for the lunar surface. The Centaur hit the surface first, closely followed by the LCROSS. The impacts were expected to excavate more than 350 metric tons of lunar material and create a crater 66 feet in diameter and a depth of 13 feet.

“The LCROSS science instruments worked exceedingly well and returned a wealth of data that will greatly improve our understanding of our closest celestial neighbor,” said Colaprete. “The team is excited to dive into data.” Colaprete said it will take “days, weeks, months” to properly analyze the data.

The Centaur and LCROSS hit the Cabeus crater near the moon’s south pole. The sun never rises above certain crater rims at the lunar pole, and some crater floors may not have seen sunlight for billions of years. With temperatures estimated to be near minus 328 degrees Fahrenheit, these craters can “cold trap” or capture most volatiles or water ice.

“If there’s water there, or anything else interesting, we’ll find it,” Colaprete said.