Update (October 17): At last, NASA has extracted a clear image of the debris plume of the Centaur rocket-body impact. The very overexposed-looking image below was taken by the plummeting shepherd probe about 15 seconds after the rocket body hit. It shows a puff of stuff (circled) some 6 to 8 kilometers wide.
The image consists of three co-added, stretched video frames. Amateur occultation timers — who are used to videoing faint events on the Moon's brilliant edges — have been lambasting the mission planners for setting the camera to give good exposures of the bright Moon, not the faint event.
A NASA feature article posted yesterday about this new development puts a positive spin on things, calling the mission "a smashing success, returning tantalizing data about the Centaur impact," and noting that "the nine LCROSS instruments successfully captured each phase of the impact sequence: the impact flash, the ejecta plume, and the creation of the Centaur crater."
"We are blown away by the data returned," says Anthony Colaprete, LCROSS principal investigator and project scientist, in the article. "The team is working hard on the analysis and the data appear to be of very high quality. . . . 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.”
See also more LCROSS images, with detailed captions.
Update (October 11): It's clear that little if anything of LCROSS's demise was seen from anywhere on Earth, a keen disappointment to professional and amateur astronomers who'd hoped to see it.
However, the results were more positive from the Lunar Reconnaissance Orbiter, which was nearly overhead in its polar orbit and only 48 miles (76 km) from ground zero.
For example, all four of the heat-sensing infrared imaging channels on LRO's Diviner instrument picked up a pulse of warmth from the impact site after the crash. According to the Diviner team's news blog, the "hot pixels" in their scans imply that "the LCROSS impact resulted in significant local heating of the lunar surface." But this by itself doesn't seem like any huge news.
The LAMP instrument (Lyman-Alpha Mapping Project) on LRO did view the debris plume from the crash against the dark sky beyond the lunar limb. "We do see a blip in total signal beginning a few tens of seconds after the impact," comments principal investigator Alan Stern (Southwest Research Institute). "There are several lines that show up, like one we think is Al III [doubly ionized aluminum]; those are most likely due to the spacecraft and perhaps some lunar material that has vaporized." Again, hardly a big finding.
Update (October 10): So far two instruments on the Lunar Reconnaissance Orbiter (LRO) have positive detections. LAMP, an ultraviolet spectrometer, has a confirmed detection of the ejecta plume, and its team has begun analyzing that data. The Diviner instrument, which measures surface temperatures, has recorded before/after changes at the impact site.
Meanwhile, astronomers have begun to assess the imaging and spectroscopic observations made with the army of powerful telescopes that were trained on the Moon's south pole yesterday morning. The following table, compiled from responses to S&T queries and other press reports, lists the professional ground- and space-based sites involved in the LCROSS observing campaign.
|Observatories Watching LCROSS|
|Apache Point||NM||3.5 m||No detection|
|CFHT||HI||3.6 m||No detection yet|
|Gemini N||HI||8.1||No detection yet|
|IRTF||HI||3.0 m||No detection|
|Keck||Hi||10.0 m||No detection|
|Lick||CA||3.0 m||No detection|
|Magdalena Ridge||NM||2.4 m||No detection|
|MMT||AZ||6.5 m||No detection|
|Mount Wilson||CA||1.5 m||No detection|
|National Solar Obs.||AZ||1.6 m||Sodium detected|
|Palomar||CA||5.0 m||No detection|
|Subaru||HI||8.3 m||No detection yet|
|GeoEye 1||orbit||1.1 m||TBD|
|HST||orbit||2.4 m||No detection|
|Odin||orbit||1.1 m||No detection yet|
Update (October 9th): At a press conference 2½ hours after the impacts Monday morning, NASA's LCROSS team members were upbeat. They reported that the spacecraft and its instruments all performed "beautifully," but warned "It takes a while to comb through the data." Anthony Colaprete, the LCROSS principal investigator, said "we saw the crater" from the Centaur rocket-body impact and recorded other high-quality data, but he declined to say anything about water yet. (LCROSS was designed to detect an amount of frost in the soil as small as 1 part in 200.)
Colaprete displayed an infrared image of the tiny impact flash a few pixels across, and showed photometry of the flash in visible and near-infrared light: a tiny bump in a light curve. An IR camera also recorded the warm craterlet left by the Centaur, hardly more than a pixel (a few dozen meters) across.
No ejecta plume was clearly detected — at least, Colaprete stressed, by the time of the press conference (but see the LRO result below). He held out hope that the probe's spectroscopic data might yet show ejecta and its composition.
Jennifer Heldmann, coordinator of the observation campaign, displayed images from ground-based observatories. Nothing dramatic was apparent, but analysis of the images and spectroscopy continues. Infrared spectra from the MMT Observatory in Arizona, taken just before and after impact, seemed to look different, but no one at the press conference would comment about them any more definitely. At Kitt Peak in Arizona, observers recorded a flare of light at the orange sodium-emission wavelength.
The ground-based videos that were presented showed a lot of changeless black shadow behind Cabeus's bright foreground ridge — but that doesn't mean that nothing may yet come of them.
Reporters quizzed the team members about the non-event the smashup certainly looked like. Answered Colaprete, "Life is full of surprises" and later added, "I certainly hope we can dig something out of there that will be telling."
Original post (8 a.m. EDT, October 9th):
Early this morning, as planned, the Centaur rocket body for NASA's LCROSS probe slammed into a permanently shadowed crater floor near the Moon's south pole — four minutes before the smaller live probe followed behind. The probe, in its final minutes and seconds of life, flew through the dust-and-vapor plume from the first impact, took data with nine instruments, and radioed it back to Earth — just before creating a second, smaller impact of its own.
Countless astronomers both professional and amateur were watching from Earth. The Moon was up in a dark, pre-dawn sky for western North America and Hawaii, where many of the world's largest telescopes were primed to grab spectroscopy of any vapor plume that became visible. Even in the daylit East, hopeful amateurs with good weather were out under a blue sky watching the crater Cabeus as the minutes counted down. And much larger numbers were watching on NASA TV.
Of course I was clouded out. But what drama on TV! We watched through the eye of the probe's camera as the probe approached the darkly shadowed part of Cabeus, frame by frame. Controllers struggled in the last minutes to adjust the image-taking rate, by the visible and thermal-infrared cameras, to cope with the unexpectedly large compressed image files that had to be radioed back.
"Mark; Centaur impact," called a flight director at NASA's Ames Research Center. The black shadow-patch showed nothing — though the probe was looking straight down into it. The seconds ticked off. In each frame the crater and its shadowed zone grew larger. Still nothing but darkness. The same, apparently, in the colorful thermal-infrared images. An announcement came that a thermal-infrared signal was detected. A few warm infrared pixels seemed to pop in and out of view. More blankness. Then the signal went dead — the probe had hit. The flight phase of the mission was over.
It should be days before the full results from the probe and ground-based are available, so stay tuned. NASA's LCROSS website will have further news updates as they are announced.
Meteoroid impacts the size of the Centaur rocket strike happen on the Moon a few times a month, but unpredictably and at arbitrary places. This one was carefully planned. Water was the treasure NASA was hunting. Certain valleys and crater floors near the Moon's poles have been in permanent shadow for millions of years. The ground here remains so cold (as low as 40°C above absolute zero) that tiny, rare traces of water vapor, and perhaps other volatiles, could condense as frost and, over the ages, accumulate. Occasional comet nuclei hitting the Moon could supply the vapor. So might atoms of hydrogen in the solar wind reacting with oxygen atoms in surface rocks.
If water exists anywhere on the Moon in extractable quantities, a permanent lunar base, and eventual colonies of settlers, would be much more practical than if all supplies had to be carried from Earth. Water isn't just to drink. Its most important use might be to supply rocket fuel (by splitting it into hydrogen and oxygen using solar energy) and raw material for manufacturing processes.
No one knew how big a plume the impacts would make. LCROSS's two main components — its bullets — were the 2.2 ton Centaur rocket that propelled the spacecraft to the Moon, and the smaller, 0.6-ton "shepherd" probe guiding both craft to the target. Several hours before the strikes, the shepherd separated and dropped far enough behind the Centaur (about 400 miles) to fly through the plume created by the Centaur before crashing itself. Both hit at 1½ miles (2½ km) per second.
Theorists predicted that the rocket's strike should kick up 350 tons of debris and create a flash in visible light. From Earth's viewpoint, the flash site was hidden by the rim of the target crater. No one knew how visible the transient debris plumes rising above the crater wall might be during the next minute or so, but LCROSS scientists estimated that the main plume might appear about as bright as the lunar surface itself in the area and, as seen from Earth, a few arcseconds in size at its peak.