Moon Crash Plume Visible to Spacecraft But Not Earth Telescopes

Article written: 17 Oct , 2009
Updated: 11 Apr , 2016
by

Nine science instruments on board the LCROSS spacecraft captured the entire crash sequence of the Centaur impactor before the spacecraft itself impacted the surface of the moon. But from Earth, any evidence of the plume was hidden by the rim of a giant impact basin, a 3 kilometer-high (2-mile) mountain directly in the way for Earth telescopes trained on the impact site, said Dr. Peter Schultz, co-investigator for LCROSS. Additionally, the crater created by the impact was only about 28 meters across (92 feet) but Schultz said the best resolution Earth telescopes can garner is about 180 meters (200 yards) across.

The science team is analyzing the data returned by LCROSS, and Anthony Colaprete, principal investigator and project scientist, said “We are blown away by the data returned. The team is working hard on the analysis and the data appear to be of very high quality.”

The team hopes to release some of their preliminary findings within the next several weeks, Schultz said at in webcast with students and teachers this week.

During the Oct. 9 crash in to the Moon’s Cabeus crater, 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.

Within the ultraviolet/visible and near infra-red spectrometer and camera data was a faint, but distinct, debris plume created by the Centaur’s impact.

“There is a clear indication of a plume of vapor and fine debris,” said Colaprete. “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.”

The magnitude, form, and visibility of the debris plume add additional information about the concentrations and state of the material at the impact site.

From images and data, the team was able to determine the extent of the plume at 15 seconds after impact was approximately 6-8 km in diameter. Schultz said the Moon’s gravity pulled down most of ejecta within several minutes.

The LCROSS spacecraft also captured the Centaur impact flash in both mid-infrared (MIR) thermal cameras over a couple of seconds. The temperature of the flash provides valuable information about the composition of the material at the impact site. LCROSS also captured emissions and absorption spectra across the flash using an ultraviolet/visible spectrometer. Different materials release or absorb energy at specific wavelengths that are measurable by the spectrometers.

the locations of the Diviner LCROSS impact swaths overlain on a grayscale daytime thermal map of the Moon’s south polar region. Diviner data were used to help select the final LCROSS impact site inside Cabeus Crater, which sampled an extremely cold region in permanent shadow that can serve as an effective cold trap for water ice and other frozen volatiles. Credit NASA/GSFC/UCLA

the locations of the Diviner LCROSS impact swaths overlain on a grayscale daytime thermal map of the Moon’s south polar region. Diviner data were used to help select the final LCROSS impact site inside Cabeus Crater, which sampled an extremely cold region in permanent shadow that can serve as an effective cold trap for water ice and other frozen volatiles. Credit NASA/GSFC/UCLA


Additionally, the Lunar Reconnaissance Orbiter’s Diviner instrument also obtained infrared observations of the LCROSS impact. LRO flew by the LCROSS Centaur impact site 90 seconds after impact at a distance of ~80 km. Both science teams are working together to analyze the their data.

The LCROSS spacecraft captured and returned data until virtually the last second before impact, Colaprete said, and the thermal and near-infrared cameras returned excellent images of the Centaur impact crater at a resolution of less than 6.5 feet (2 m).

“The images of the floor of Cabeus are exciting,” said Colaprete. “Being able to image the Centaur crater helps us reconstruct the impact process, which in turn helps us understand the observations of the flash and ejecta plume.”

Sources: LCROSS, LCROSS webcast

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14 Responses

  1. Dave Finton says

    It looks like a bulls eye to me

  2. Jim Krug says

    I’m sorry, but I find this entire situation VERY suspect for the following reasons:

    1. I figured that going into this mission, something would go wrong and we wouldn’t be able to see the plume from Earth as NASA predicted.

    Now while I prefer to lean towards some reasons that many here would find questionable/laughable, even if you DON’T believe in any Moon habitation angle, I think we need to ask why in the world were NASA’s calculations off so badly?

    According to this article, they were predicting a crater over 180m across, but ended up getting one over 8x smaller! That’s a pretty significant miscalculation on the part of an organization that had ample time to prepare for all possibilities.

    2. If 9 LCROSS instruments supposedly captured “every phase” of this impact, why in the world didn’t the public get to see it? All we saw was the screen blur out and go bright white, and that was it. Again, I find this highly suspect, since the public saw so little, yet we were supposedly watching through one of the same instruments they’re now saying worked flawlessly.

    3. I don’t really find the still images of the “plume” very compelling. Not only could that simply be sunlight reflected off of a rough part of the Moon’s surface, but the same effect could easily be attained using Photoshop or any other digital editing application.

    Again, I think I could’ve believed these images/stories more if what the public saw even remotely resembled what NASA and this investigative team are saying actually happened. It didn’t.

    JIm

  3. Torbjorn Larsson OM says

    I prefer to lean towards some reasons that many here would find questionable/laughable,

    No, they don’t reach the level of questionable nor are they laughable, as all conspiracy theories strain credulity to the point of breaking way before. Such “ideas” (and I use the term very loosely) are nuts, and they are a sad testament to the inability of individuals to learn about their environment.

    But if I disregard the idiotic framing and the possible trolling that usually follows it, there are for once real questions posed among the garbage here.

    As regard crater size, it’s not one of them, it’s a failed attempt to read the article. (Perhaps the commenter has confused observing the crater with observing the plume.) But a note on crater size, because it is interesting: I’m not sure if the LCROSS team ever considered crater size, but I do seem to remember they did a dress rehearsal with another probe/rocket stage a way back. It must be near impossible to estimate crater size/ejecta plume because the regolith properties at the target is unknown (gravel or rock?), but it turns out they did a fair job:

    “”We shied away from it because of topography. It’s large, 100 kilometers across and fairly deep, 3-4 km deep. And on the side that faces Earth there’s a mountain about 2 kilometers tall. We feared we’d have trouble getting ejecta in view of Earth. New topography measured by Kaguya and by LRO LOLA revealed a serendipitous situation for us. For our impact date, the Sun will be shining in through a cleft right along the rim of the crater. The cleft will let sunlight in that streams across the floor, so the ejecta gets into sunlight early, after only about a kilometer rise. So that’s great news.

    “We looked at where we’d want to impact — coldest temperatures, smooth flat floor, and we found that we could find a spot that limited the blockage from the mountain because there’s a saddle in the mountain; we’ll be able to see the ejecta from Earth after only about 1.5 kilometers of rise. One other aspect that made it more attractive was backlighting. Cabeus A would have had a bright crater wall behind it — you’re looking at faint dust against a bright background. With the new Cabeus target, the far side of the valley actually casts a shadow behind where we’re impacting.”

    So AFAIU they got a plume extent (6-8 km) that was slighter larger than their low expectations (3 to 4 + 2 = 5 to 6 km). But as it was on the low end of brightness it seems it was (too?) hard to observe from Earth. Despite all the effort they put in to maximize contrast and visible time by changing target.

    As regard the scientist plume presentation and its timing, it’s of course early stages. The first results have IIRC been said to be expected to be released in 6 months time. The scientists have to model the instruments and the observations in concert, and all of that will take time.

    I’m frankly glad that scientists have been media savvy enough to release very preliminary findings. Used to be a time then that wouldn’t happen, mostly because it leads to all sorts of gross distortions and misunderstandings, that draws attention from the science, by the public as witnessed on the LCROSS mission. Not to mention the ever popular conspirationist crackpot “analysis”…

  4. Torbjorn Larsson OM says

    Speaking of preliminary data, we have also this on the mentioned LRO observations of the plume:

    “In the meantime, far-ultraviolet spectra taken by another craft, the Lunar Reconnaissance Orbiter, as it flew over the impact site shows no obvious signs of water. Instead, the spectra show signs of what may be iron and mercury, says Gladstone, a mission scientist.”

    For the conspirationists out there: the “no obvious signs of water” observation doesn’t translate to “no water” of course. Hopefully we will learn within 6 months time.

  5. Maxwell says

    I got up that morning with the intention of taking my binoculars to look for the explosion, but it turned out to be brighter than I expected and overcast.

    …then I reasoned (for the first time since hearing about lcross) that I’d be using a pair of astronomy binoculars to look at an area the size of Texas for an event about the size of a water heater exploding.
    Anything short of a nuclear blast wasn’t going to be visible, so why stand in the rain looking for it?

    Yes the CGI and news media drummed up this image in my head of a spectacular mushroom cloud, but a few days later they also had me thinking a six year old boy could be hoisted aloft by a half filled mylar bag of helium smaller than a compact car.

    The television lies!

  6. Conspiracies, no. Wishful reporting, often added up on top of the core finding, regrettably, yes.

    There’s a debate going on about where to go next, Mars of Moon, and many releases are timed and phrased in order to achieve maximum effect.

    Such was the very misleading “liter per ton” phrase that got attached at some stage to the solar wind induced water measurement, and so is the reluctance to release preliminary information here. Does anyone really think that if there was water in the plume, they’d wait 6 months to announce it?

    (The other explanation, btw, is that the results were so astounding that they are waiting for further analysis to rule out a miscalibration or other sources of bogus data. You know – spectrograph shows clear evidence of Camembert, with traces of Brie and Cheddar)

    As for crater size, yeah, it’s impossible to really predict – not even within a factor of 10. Not based on modeling at least.

  7. Lawrence B. Crowell says

    The crater sizes reported strike me as a bit strange as well. A solid body as with a meteoroid will create a reasonable crater. If you take the kinetic energy of hydrodynamics for the motion of material out of a crater and make that equal to the kinetic energy of an impactor you get a relationship between the radius of the impactor and the crater of the form

    R_{crater} ~ Ar*v^d,

    where v is the velocity r the radius of the impactor A a constant and d ~ 5/2. As a rule of thumb here a 1meter radius meteoroid moving 10km/sec will carve out a 20 meter width crater. Yet the LCROSS monitored a rocket stage impact, which was essentially a large empty can. I strikes me as odd somebody would have though this would create a 180 meter wide crater.

    LC

  8. LC – I was not familiar with this formula for the outflow of material. As you imply, it assumes that all the energy went into moving material outwards, which is a very efficient mechanism. It means the ground didn’t warm up, no compression waves diffused energy into the bulk of the moon, the ejecta was cold, etc. In a way – an elastic collision between the impactor and the ejecta.

    So if the energy calculation really implies 20 m, then in reality it would be smaller still.

    That said, their focus was on the evaporation plume, which sound realistic, since we’re only looking for trace amounts. The emission spectrum can be observed against the dark crater, which is nice, and they had this bit about getting the plume illuminated from the side so that they can read the absorption spectrum before it is swamped by lunar surface reflections.

    So all in all, 6 months to come up with data? They should release what they know. Even if there’s no water, it is still a result. If there’s data, then the experiment is a success.

  9. Maxwell says

    Problem is the data as it stands could be used to affect lunar exploration plans. Water on the moon means our future plans must include moon bases and polar exploration missions.
    A lack of water means there isn’t as much interest in visiting our nearest neighbor, as sustaining life there would be much more difficult at best.

    I don’t think the LCROSS planners want to say anything about water on the moon until they have a solid answer, one way or another.

  10. Jim Krug says

    [i]”No, they don’t reach the level of questionable nor are they laughable, as all conspiracy theories strain credulity to the point of breaking way before. Such “ideas” (and I use the term very loosely) are nuts, and they are a sad testament to the inability of individuals to learn about their environment.
    But if I disregard the idiotic framing and the possible trolling that usually follows it, there are for once real questions posed among the garbage here.”[/i]

    See, I found the rest of your post very interesting and informative, but this initial part made it tough to get there.

    It was completely uncalled for. Although I mentioned my beliefs in passing, I never elaborated on them in the slightest, nor allowed them to affect my observations of the matter.

    Simply dismissing the idea of other civilizations being out there as “nuts” is akin to people dismissing Aristarchus as “nuts” because he dared to think the Sun was at the center of everything, and not the Earth.

    Frankly, that kind of closed-minded response concerns me, because when scientists start doing that- drawing conclusions without looking at all of the data in front of them- they themselves are no longer following the scientific method that is supposed to be their code.

    JIm

  11. ND says

    Jim Krug,

    “Now while I prefer to lean towards some reasons that many here would find questionable/laughable, even if you DON’T believe in any Moon habitation angle, I think we need to ask why in the world were NASA’s calculations off so badly?

    Did I miss something? Were you suggesting that there are inhabitants on the moon? And NASA was aiming at them? Is this correct?

    Although I mentioned my beliefs in passing, I never elaborated on them in the slightest, nor allowed them to affect my observations of the matter.

    Sounds like you were purposely implying. You need not have to elaborate.

    Frankly, that kind of closed-minded response concerns me, because when scientists start doing that- drawing conclusions without looking at all of the data in front of them- they themselves are no longer following the scientific method that is supposed to be their code.

    Classic textbook-case. My ideas are being rejected and laughed at because those scientists, who have far more advanced in knowledge of the field, are close minded and don’t know how to do science.

  12. kootstar says

    Unfortunately, I (simple minded as I am) see nothing but emotional argueing going on here. Yes, water on the moon would be wonderful, cause less cost in supply and renewal of supply at post. But think of the work done at ISS already. More expensive to supply the Moon, but it could be done. Regeneration of used supply could be done with even today’s sciences. On moon supply could make the whole project quicker and less costly, but whether it is or is not there, anywhere, this could help tell the history and composition of the place and even some more facts of true relation to the planet we all live on. Whatever the composition of ground impacted by that one program may not tell the whole story. There are other places to look, and underground may be even better. So please, let’s not squabble like mad kids?

  13. Lawrence B. Crowell says

    @ CrazyEddieBlogger:

    I am not an expert on those problems. I remember a few things about it from my celestial dynamics days. It could be that you get a wide but shallow crater. I just find it amazing that an empty shell of material would generate a crater that size.

    LC

  14. Jim Krug says

    “Classic textbook-case. My ideas are being rejected and laughed at because those scientists, who have far more advanced in knowledge of the field, are close minded and don’t know how to do science.”

    That’s pretty hilarious. So basically all the smart kids don’t believe it, so it’s stupid if you do…

    …even though the “smart kids” never took the time to actually see what evidence was out there, because they were too busy calling it nuts.

    Bottom line: Total independent of the life on the Moon debate, this impact did not go at all as NASA said it would. I think we should raise questions as to why it didn’t, since the magnitude/visibility of the impact was so different than expected.

    JIm

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