Moon Crash Delivers No Obvious Plume

By Ron Cowen, Science News

The one-two punch of crashing a booster rocket and its mother craft near the moon's south pole didn’t kick up dramatic and visible plumes as hoped, but scientists reported October 9 that the mission had gathered enough data to tell whether the crater contains frozen water.

At 7:31 a.m. EDT on October 9, an empty rocket booster was deliberately crashed into Cabeus, a shadowed crater near the moon’s south pole where ice is suspected to reside. Astronomers watched through telescopes and the visible-light camera aboard the rocket’s mother ship, NASA’s LCROSS, or Lunar Crater Observation and Sensing Satellite, spacecraft. No plumes were visible. Amateur astronomers using medium-sized backyard telescopes have not reported seeing a plume, which had been predicted to rise above the crater rim and be visible from Earth.

About four minutes after the first crash, LCROSS took its own death plunge into the crater. Even without a visible plume to ooh and aah over, the data recorded by LCROSS as it homed in on Cabeus and flew through the debris from the first impact will still be invaluable for searching for frozen water, said Barbara Cohen of the lunar precursor robotics program at NASA’s Marshall Space Flight Center in Huntsville, Ala. Cohen was one of about 200 astronomers in Fajardo, Puerto Rico, attending the annual meeting of the American Astronomical Society’s Division for Planetary Sciences and who gathered together to view the LCROSS images on a big screen.

LCROSS detected a small rise in the amount of infrared light coming from the crater, a sign that it had seen the thermal flash from its spent rocket boost. LCROSS also confirmed that the crater had brightened at both infrared and visible wavelengths. The brightening indicates the booster's crash had kicked up material.

The spacecraft also recorded variations in the intensity of visible and ultraviolet light, said Anthony Colaprete, LCROSS principal investigator and project scientist at NASA Ames, during a 10 am press conferences from the NASA Ames Research Center in Mountain View, Calif. “I’m excited that we saw variations in the spectra,” he said.” The information is there, we just have to get to it.”

“We have a tremendous amount of data” to analyze and piece together, added Jennifer Heldmann, also of NASA Ames and coordinator for the LCROSS observation campaign, also during the press conference.

Astronomers are scrutinizing the data as well as that taken from a slew of other telescopes, including the Keck Observatory atop Hawaii’s Mauna Kea, to look for the fingerprints of water vapor or for one of its fragments, the hydroxyl radical, which contains one oxygen and one hydrogen. The presence of either fingerprints or fragments would indicate that the part of the crater floor impacted indeed contained ice.

Keck astronomers did see a brightening in the spectroscopic readings, indicating that Keck recorded the plume. The astronomers will not know about water vapor, as that data will take a little longer to analyze.

Astronomers using the 5-meter Hale Telescope at Palomar Observatory near San Diego also saw no plume. By comparison, when the Japan Space Agency’s lunar-orbiting Kaguya spacecraft was deliberately crashed into the unlit side of the moon in June, a 4-meter ground-based-telescope could see it. The LCROSS rocket booster weighed about two tons and might have made a smaller impact than the three-ton Kaguya did.

Heldmann confirmed that the Hubble Space Telescope, looking not directly at the crater site but off to one side of the moon, had recorded images and spectra of the one-two punch into Cabeus. Images from Hubble should be transmitted to Earth around noon October 9, and spectra about 3 pm. Both are expected to be released by the end of the day.

“I think if we see anything [in the images] it will be awfully subtle,” says Ray Villard, public affairs manager at the Space Telescope Science Institute in Baltimore.