Moon crash delivers no obvious plume

But the two impacts still yield data that could help in search for water

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.

The lunar crater Cabeus appeared untouched 10 seconds after a booster rocket was deliberately crashed into it. While the lack of a visible plume from the crash was disappointing, early data hint that the impact did kick up material that could help in determining whether the crater contains water. IMAGE FROM: Hale Telescope at Palomar Observatory

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.

A newly installed camera and a revived spectrograph on the Hubble Space Telescope observed the moon just before LCROSS and its rocket struck. Looking at the southern limb of the moon, Hubble’s Wide Field Camera 3 saw no sign of lunar material kicked up into view by the crashes, NASA announced late on October 9. A preliminary analysis of ultraviolet spectra taken by the Space Telescope Imaging Spectrograph showed no obvious sign of hydroxyl (OH), a fragment of water that might be expected to be produced if frozen water were vaporized by the impacts, said Alex Storrs of Towson University in Baltimore.

“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.

During the impact event, Michael Kelley of the University of Maryland in College Park and David Harker of the University of California San Diego observed the moon with NASA’s Infrared Telescope Facility atop Hawaii’s Mauna Kea.

“The data we took is great, but we can’t yet say if we saw any plume,” says Kelley. “It isn’t so much disappointing as it is puzzling” why the lunar soil that must have been kicked up by the crashes wasn’t immediately obvious, he adds. “We have a lot of work ahead of us to see what happened.”

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