The LCROSS Impact, Continued

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.

Extensive image processing of images taken by the LCROSS shepherding spacecraft 15 seconds after the Centaur rocket's demise reveals a dim debris plume (6 to 8 km across) in the shadowed part of Cabeus crater.
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.

LRO's Diviner instrument (here sensing wavelengths from 25 to 50 microns) recorded the lunar surface before and after the LCROSS impact and detected the resulting crater (arrow).
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.

The inscrutably dark interior of Cabeus crater dominates the center of this frame from the Palomar 200-inch telescope, taken 10 seconds after the Centaur rocket body impacted behind the bright foreground ridge. This is an infrared view at 2.1 microns wavelength. No trace of a debris plume is evident. More and larger Palomar images.
Palomar Observatory
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
Allen arrayCA(radio)TBD
Apache PointNM3.5 mNo detection
CFHTHI3.6 mNo detection yet
Gemini NHI8.1No detection yet
IRTFHI3.0 mNo detection
KASSIKorea1.8 mTBD
KeckHi10.0 mNo detection
LickCA3.0 mNo detection
Magdalena RidgeNM2.4 mNo detection
MMTAZ6.5 mNo detection
Mount WilsonCA1.5 mNo detection
National Solar Obs.AZ1.6 mSodium detected
PalomarCA5.0 mNo detection
SubaruHI8.3 mNo detection yet
GeoEye 1orbit1.1 mTBD
HSTorbit2.4 mNo detection
Ikonosorbit0.7 mTBD
Odinorbit1.1 mNo detection yet
  • The ejecta plume was seen by the ultraviolet spectrometer aboard NASA's Lunar Reconnaissance Orbiter circling the Moon — LCROSS's companion mission. In addition, LRO's imaging radiometer detected the warm impact crater.
  • At Keck Observatory in Hawaii, Diane Wooden (NASA/ Ames Research Center) used the 10-meter Keck II telescope with its Near-Infrared Echelle Spectrograph (NIRSPEC) to look for the signature of water vapor. According to a Keck press release, "Wooden and the other LCROSS astronomers are currently evaluating the spectroscopic data collected at Keck and the other Mauna Kea observatories for the water-vapor signature. The team plans to report their results early next week."
  • "Inconclusive" results so far from the 8-meter Gemini North telescope in Hawaii.
  • Nothing obviously seen by three large telescopes at Apache Point Observatory in New Mexico.
  • Video of the non-detection from Lick Observatory.

    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.

    Cabeus is the big crater nearly filling this frame from the LCROSS probe as the probe closed in. The rocket body had already hit in the dark, permanent shadow filling the top of the crater.
    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.

    The shepherd probe (center) sails into the impact plume from the rocket body in this frame from a NASA simulation of the expected sequence of events.
    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.

  • 14 thoughts on “The LCROSS Impact, Continued

    1. Ken

      A nice view of the moon. tried both my 12.5mm and 6mm on a 10″ dobsononian but no plume. Me and my boys are still excited to be there when it happened. no regrets.

    2. Marc

      An idea of smallness hits me when I read through all this. We are so small, especially compared to the obvious vastness of space, the moon, we cannot even see direct results from a two-ton vehicle we send down to slam into the surface.
      We are small.
      Accept it.

    3. Richard

      Watched with my 6-inch refractor in Colorado. Went back inside to watch NASA TV. If they couldn’t see it with the shepherd, I certainly wasn’t going to see it with my scope!

      But it was a beautiful morning! …a little snow on the ground

    4. Kent Blackwell

      I had three telescopes set up in the
      driveway; a vintage 1952 Unitron f/15 refractor, a homemade 12.5″ f/6 Newtonian reflector and an Orion 10″ f/4.7 IntelliSCope. Three of us watched intensely as we saw, well, NOTHING. Two other friends were watching from their post miles from me and they also had negative results.

      Although the results were negative it was still fun watching. I had a mini star (Moon?) party in my driveway, complete with donuts, coffee and even Moon Pies. To top things off the background music included Jacques Offenbach’s, “Voyage To The Moon!”

      Kent Blackwell
      Virginia Beach, VA

    5. Gavin Eadie

      You note:

      “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.”

      but, in fact, the impact was visible on NASA TV. Just as that phrase was beginning, the whole phrase being, “All stations, Flight. Mark! Centaur impact” the NASA TV transmission switched to near infra-red (NIR) images and you see one frame with no sign of impact, then three (maybe four) frames with a tiny blossom of color at the impact site, then it’s gone.

      I missed it too when I was watching NASA TV live, but replaying that moment, it’s quite obvious.

    6. Tim

      I set up my 10″dobsonian mounted reflector to observe the impact. I was observing at 115X magnification from 4 to 5 AM PDT. Despite predictions that amateur telescopes 10″ and larger should be able to see this, like others on this blog, there was nothing to see. When I read on this post that even the large ground based telescopes on the ground could not see it, at least I knew that my suspicions of a non-observation were confirmed.

      All was not lost however. I am not a regular lunar observer, but what struck me was the last glimpses of sunlight on high points around the crater rims along the lunar terminator.

      I next turned to Mars to see a visible tiny disk. Then the clouds came rolling in with an approaching arctic cold front.

    7. Scott

      Used my 8″ dob with parks primary and a barlowed 7mm nagler for ~350x and I didn’t expect to see much but thought I would try anyway. I used that high of magnification based upon suggestions I had read here and it was pushing the seeing a bit for my location (Sacramento, CA area) but it was amazing how much detail I was able to view.

      For the 15 minutes leading up to impact the dot of light and the “nose” on the ridge at the edge of the moon (as also seen in the Palomar image) were really viewable and generally pretty sharp overall with the seeing only causing very brief moments of blurring. (In fact ny view was generally like that image from Palomar but less magnified and wider field.) The only thing I noticed is that for about a minute after the time of impact (based on my clock) both of these features became very blurred and the dot of light basically disappeared. It’s as though the seeing took a real dive during that period.

      Curiously it didn’t seem like the detail in other parts of the field, such as the textures near the edge of Moretus, were affected. However, I’m sure it had to have been a coincidence as the area that appeared to be affected was far more than a magnitude of order larger than the predicted plume size.

    8. bob kelly

      Thanks for the update, esp. the list of observatories. It’s helpful to have a roll call of possible sightings.
      Thanks, too, to the observers who have reported here.
      We were clouded out in the NYC area, although it would have been after sunrise here.

    9. Ken Lum

      I was at NASA Ames watching the real time transmissions from the LCROSS satellite as they came down. I was actually rather surprised by the lack of an impact flash. This is amazing when one considers how bright the flash was from the Deep Impact mission to Comet Tempel 1(9P/Tempel) in 2005. It is even more surprising given that lunar impact flashes have been seen numerous times before presumably from meteor impacts. e.g.( among many such observations.
      Rather than express disappointment over this apparent null result, I would rather look upon this as a significant mystery that could lead to an unusual explanation for the nature of the lunar surface if there is appropriate followup and reconnaissance. Indeed, it could lead to a new explanation for the surfaces of many solar system bodies.
      We should all be reminded that perhaps the most significant null result in the history of science was that of the Michaelson-Morley experiment of 1887 which failed to find evidence of the luminiferous aether which supposedly allowed the propagation of light in space. This led to the discovery, by Einstein, of Special Relativity in 1905. And so null results can lead to major discoveries, to say the least. In the LCROSS case, only time (and perhaps money!) will tell. And so NASA needs to explain this result in terms like this, although I admit this may be a hard sell to unsophisticated taxpayers.

    10. Michael C. Emmert

      Thank you, Ken Lum. :) Maybe we didn’t see any dust because there was no dust? Hmm…how could that be? Maybe a layer of ice a couple of feet thick? This might get very interesting.

    11. Graham Wolf


      Here in New Zealand, we had several days of storms, high winds, and local flooding in the capital. I’m ex Carter National Observatory of NZ, with nearly 5 decades of frequent lunar observing.

      Tested both a 30cm f5 and an 18cm f5 Newtonian a few days before the scheduled impact… when I had briefly clear skies. The central mountain in Tycho was easy to see down to about 4km resolution at 600x. The Cabeus region (near the South Lunar Pole) at 300x, 600x (750 – 900x with the larger instrument and Barlow projection), was also visually pre-tested earlier in the week. Local Hutt Valley skies did indeed clear at near dawn (~ 5 hours after the impact event), but only after a vicious 3 day storm!

      I was beaten by the stormy weather “down under”!


      Graham Wolf (Lower Hutt, New Zealand)
      Barber Grove Observatory (BGO) 41:13:42.3 S, 174:54:09.9 E
      2.2m amsl (1949 NZ Datum)


      A nil result from New Zealand. Storms and floods for 3 days on end with only about 30 min of clear skies between 6 – 8 hr “blitzing” cold fronts. Skies did clear ~ 5 hr after the LCROSS impact event. Had 18cm f5, and 30cm f6 Newtonians set up at ~600x ready to “go”. Congrats to NASA on a great mission… videos reminded me of the Ranger impact photos of Alphonsus in the 1960′s. Hope the selenophysicist got some useful data.

      Graham Wolf (Lower Hutt, New Zealan)

    13. Dennis Young

      It is sad that so far the return data has been little in regards to positive feedback. Main part of mission was to see if frozen ice exist and of course if there was even a hint they(Nasa) would of comment on it, by now. They mention they saw a small plume in a very sensitive instrument, but any object hitting the moon would of sent a dust plume above the surface. Hoping for further updates that are more inspiring is all we can hope for.

    14. Rosemary Killen

      Your posting concerning observers watching the LCROSS impact contained an error. The 1.6 meter McMath-Pierce solar telescope on Kitt Peak was observing, not the 4 meter, and we did detect sodium.

      Observers were Rosemary Killen, Andrew Potter, Claude Plymate and Shantanu Naidu frrom Goddard Space Flight Center, National Solar Observatory and the University of Maryland.