LCROSS plume detected, but not from Earth

By Phil Plait | October 19, 2009 11:45 am

When NASA slammed the 700 kg (1500 pound) 2400 kg (5200 pound) Centaur rocket booster into the Moon on October 9, the hope was that it would make a plume visible from Earth. Terrestrials were disappointed, however, when none was seen.

However, a better view was to be had by LCROSS, the Lunar Crater Sensing and Observation spacecraft, which shepherded and closely followed the rocket booster, impacting itself just minutes later. From its much closer (and doomed) location it spotted both the plume and the flash of impact! Here’s the plume:


I’ll be honest with you, it’s not much to see. For some reason, the plume was not several kilometers high as hoped, but instead more like only one or maybe two (and, it seems, blocked from our Earthly view by the rim of a crater). In the above image, taken 15 seconds after the booster impact, the plume was 6-8 kilometers wide. The fact that it was not as bright as hoped is itself interesting, however! The actual plume brightness was at the low end of what was expected, which may be due to the nature of the material it slammed into.

lcross_impact_midirThere was never really a chance to see the flash from Earth, since it was at the bottom of a crater blocked from our view. But LCROSS was directly above the crater when the Centaur hit, and took several images, including the one shown here right at the moment of impact. This image shows the flash in the mid-infrared, beyond what our eyes can see but where a lot of the energy of the impact went. Other images can be found on the NASA site.

The crater carved out by the Centaur was less than 30 meters across. That’s far too small to be seen from Earth (our limit, even with Hubble, is more than 100 meters in size), but the orbiting Lunar Reconnaissance Orbiter should be able to see it easily, and in fact did take observations of the impact just a minute or so after it happened.

All of these data are being analyzed right now. Did any of those instruments see the signature of water in the plume? Did the much larger LCROSS impact (it had a mass of 2000 kg) dig up any water? No one’s telling right now, but I suspect we’ll know soon enough. You can read more about this at Universe Today.

Update: Somehow, in my head, I got the masses of LCROSS and the Centaur reversed. Apologies, and thanks to IVAN3MAN for correcting me!

CATEGORIZED UNDER: NASA, Pretty pictures, Space

Comments (22)

  1. Man, I want to hear more NOW! :) Almost reminds me of that SMBC cartoon where they talk about splitting up the findings.

    (Goes off to Google)

    There we go, the funny:

  2. phillip M

    I know this is a little off topic, but there probably won’t be any “this blog is suppose to be about astronomy” posts.

  3. Trebuchet

    Something I’ve been wondering about on LCROSS: One of the hoped-for results was to see water in the plume. But the Centaur is a LOX/LH2 rocket. Wouldn’t residual fuel/oxidizer mess up the results? I’m sure they’ve figured out how to compensate for that; I just haven’t seen it discussed.

  4. Charles

    Those scientist bastards!!!! Now they messed my horoscope and spiritual … uh … ley line … uh metaphysical … ummm … look! A butterfly!

  5. I come here to read about Antivaxxers, but it seems like every other post these days is about outer space or planets or telescopes or something. What happened to this place?

    I guess I’ll be removing BA from my reader.

  6. Torbjörn Larsson, OM

    @ Trebuchet:

    “With regards to the Centaur we are being very careful to purge as much of the rocket fuel (hydrazine, liquid oxygen and hydrogen) as possible so as not to contaminate our measurements.” [NASA LCROSS FAQ.]

  7. Likeshadow

    ON contamination with regards to water detection, all sources were considered, including Centaur batteries (largest contributor), Oxygen and hydrogen left in the tanks (huge problem, requiring serious amounts of attitude control due to the residual pressure leaks from the tanks even after a major venting procedure to get rid of as much as possible), and the insulation foam which had absorbed water in the humid Florida air and then it was frozen when the tanks were filled (we performed 3 ‘cold-side bakes’ to try to offgass as much of this as possible. Final assessment is in the neighborhood of 40-50kg of water or products that could combine to make water. Based on instrument sensitivity, they would be unable to detect water below about 400kg assuming we hit a dry patch and were only detecting the water we brough with the Centaur. ULA requirement was to deliver a Centaur that would have less than 100kg of water at time of impact, which they met very well (required extensive new venting procedure, but no physical changes to the vehicle).

  8. gss_000

    New Scientist has a couple of articles about why they think there wasn’t much to see. Instead of acting like a cannonball hitting earth, like what I think we were expecting, it’s more like a hollow ball hitting a pile of flour. A lot of the impact was absorbed, plus they purposefully did not want to create a deep crater otherwise it would ruin the goal of seeing what is close to the surface.

    Frankly, I’m pleased the mission worked at all. This was really rushed in terms of space missions, so I was half expecting it to fail. That they’ve gotten this much out of it so far is great and I can’t wait for the analysis.

  9. Charles & Carl:
    You kill me! :LOL:

    I think it -DID- hit water ice, but it was spongy from eons of sublimation. The interstices of the ice absorbed the impact’s energy and little ice shot up. This is a good thing as we don’t really want to waste the precious ices, just detect a little of it.

    I just had to make a blog post on all this last week so you can click on my name and read it all there…

  10. Trebuchet

    Thanks for the explanations on the considerations for water carried along with the centaur! I guess I’m still not to old to learn something.

  11. I wonder if the whacking-things-into-it approach is the way to go, actually. I don’t think we got any conclusive data from the Lunar Prospector or Kayuga impacts either.

    Maybe one of the Lunar X-prize landers could be sent to the South Pole with a flashlight and a camera to go check it out first-hand!

  12. awesomekip

    “When NASA slammed the 700 kg (1500 pound) Centaur rocket booster into the Moon”

    “Did the much larger LCROSS impact (it had a mass of 2000 kg)”

    Isn’t it the opposite? I thought the LCROSS (shepherding spacecraft) was about 700kg and the Centaur upper stage was 2000kg.

  13. ARJ

    Forget about the water, DON’T you people see the face of that gargoyle in that crater/shadow formation; had to be sculpted by SOMEone….

  14. Chas, PE SE

    >>>>The fact that it was not as bright as hoped is itself interesting, however! The actual plume brightness was at the low end of what was expected, which may be due to the nature of the material it slammed into<<<

    That's the great thing about science–when an experiment is done, it's interesting. When an experiment gets different results than expected, it's even MORE interesting!!

  15. Chas, PE SE

    Ack, I used “interesting” at least 15 times in that last….


    @ awesomekip (#13),

    It is the opposite: Centaur — 2,249 kg (4,958 lb) (min.); LCROSS — 621 kg (1,369 lb) (min.).*

    It appears that Dr. Phil Plait got his facts transposed; I made a similar boo-boo on the “Worlds alien and familiar…” thread. (Tip: Always drink strong coffee before posting!)

    *Source: Wikipedia — LCROSS.

  17. Taunide

    From what I understand it would be a good sign if they DIDN’T dectect water in the ejecta. There are two ways the water could be distributed. 1.) Like dew on a wet and cold morning. That would make harvesting it quite complicated. You would need to graze of big patches of ground to get a mentionable amount of water.

    2.) More or less like a frozen Lake. Much higher concentration of Water in a small spot.

    When water IS present, and the results of Miranda, Kaguya etc hint to that, than the second option would be more desirable for future colonisation.

    Maybe someone should send a hovering Probe with strong lights… Maybe the Lunar Lander could be tested there. Unmanned of course.

  18. d knights

    They should have created and slammed a whale into the moon via zaphods infinity drive. that would have done the trick.

  19. Sili

    The SGU just kwetched about how disappointed they were and that Nasa really had overhyped this. “Wah wah, we couldn’t see anything. Baaaaad Nasa!”

    It’s a fragging rocket being shot into the Moon! That can’t be overhyped. Annoying that the felt the need to whine like that. It’s a good thing(tm) that the scientists were excited like that. You don ‘t get the public engaged by being mealymouthed.

  20. Heroh

    Rant all you want, Sili. Apparently it can be, and was, overhyped (judging by the reaction of the slack-jawed average joes who would never have been involved, but were; For the first time in their lives they were moved to drag their attention away from reality tv for one moment, at least).

    I’m not saying scientists shouldn’t be excited – but why do they even need the public ‘engaged’? Funding. It’s not like they are doing it to receive more ‘kvetching’, as you put it. So they public-relationed it to death, for money, and then didn’t deliver. We all know everyone was told to get out their big fancy telescopes and pocketbooks for the main event.
    Have you ever even BEEN to NASA? I have. It’s 1 part hard science, 1 part disneyland marketing.

    I’m not saying you can control experimental results – but don’t turn around and say NASA didn’t do what they most certainly did, or try to rationalize it after the fact.

    I am a proponent of science and all that it entails for us and our future -but don’t hand me an apologist’s line because you don’t like the blowback from failed PR.
    NASA will have to suck it up, and so should you.

  21. Kaleberg

    I’m not surprised by the muted impact. The entire surface of the moon is covered with a mix of rocks of varying sizes. Piles of rocks are your best defense against artillery because all the energy gets absorbed by all the dumb rocks. If there was just one stupid rock, you might crack it into lots of pieces and see something, but cracking up a pile of gravel, size, assorted, just slightly downgrades that to a pile of gravel, size, assorted minus, and you don’t see squat.


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