If the rocket stage happened to impact on a surface which was far off the horizontal, the ejecta plume coming out would be substantially less than predicted. For instance, an impact into the side of a cliff or steep slope, or the side of a big boulder, would see most of the initial ejecta thrown downwards. Only a small part of the rebound from that would end up exiting the crater, with greatly reduced energy. This might explain the lack of observed plume.

Of course, the chances of this also happening to the chaser satellite are low. However, given its much smaller size, I'm not sure what the initial expectations were of a plume from that, if any.

I'd hate it if NASA got so conservative that they didn't alert people to the possibility of something spectacular. All they really needed to do here was to say, up front, "Well, there's a possibility that no one will see anything from the ground, but there's ALSO a possibility that it'll be visible in telescopes as small as 10 inches, so it's worth taking a chance and watching." I'll bet a dollar to a doughnut there were scientists who strongly advised NOT hyping this, given the uncertainties, but they were overruled by PR types.

I can't entirely blame the PR guys, since public support is essential for funding, but it wouldn't have been THAT hard for them to hedge a little bit. Heck, someone once tried to explain to me why people watch things like football, basketball, baseball, etc. by saying that sports are fun to watch because "no one knows what will happen." Putting in some uncertainty in their claims might make these events MORE popular.

@nprev are we showing our age by remembering Kohoutek? Even a Geraldo reference seems dated now! :-)

--Greg

Of course the meteor hits might be easier to see from Earth since they wouldn't usually be hidden from direct view in the floor of a crater. On the other hand the shepherding craft should have seen more having that direct view.

And as a colleague asked me, if the Centaur was oriented sideways, would it be less likely to be buried?

If I understood correctly, a sideways hit (as well as a hit where the Centauri would be vertical) were unfavorable. An angled hit would allow for more ejecta. As for impact flash? No idea.

Not really comparable, but Lunar Prospector (far less mass, less speed --> less kinetic energy) made an almost grazing hit in 1999 but it also failed to raise any detectable plume

I think there are two variables here, one is the trajectory of the spacecraft, and the second (that I was wondering about) is the attitude or orientation of the spacecraft.

With an impact in such a permanently shadowed region, how high should the plume ejecta rise so that they can reflect sunlight? Was there any prediction for that? I just think there is not much light there to reflect the plume dust, even if the plume is extended. Still, the detectors at other wavelengths should have seen more...

As kenny said, the details of the particular terrain it hits matter too. This was mentioned in the post impact press conference.

It appears the LCROSS team believed there was a high probability that it would visible in modest size telescopes, but I'm sure they knew other outcomes were possible. They probably didn't communicate this as well as they could have, but such subtlety would almost certainly have been lost on the press anyway.

Elias: There definitely were predictions and models. You can find some of them on the lcross site.

Without time to digest the science result, that would be an absurd statement to make . Given that a bright plume was considered a possibility, NASA would be taken flack had it happened and the didn't alert people. Many people thought SL-9 would fizzle. What if NASA had played it down because we might not see much?

As (sort of) a member of "the media," I feel like I should speak up here. I had figured that people with telescopes on the smaller end of the scale probably wouldn't see anything. But given that there was a big effort to organize amateur astronomers (or at least provide plenty of relevant, up-to-the-minute information to them), and the organized events run at bigger observatories, I never, ever, once imagined that the biggest telescopes on the planet wouldn't be able to see anything. Frankly I'm still surprised and confused about the fact that even Palomar didn't see squat. I think it's totally reasonable to be surprised about that.

From my point of view, reporting on this event, I was never particularly interested in the view from telescopes of any size. I was wholly focused on the shepherd spacecraft. Everything seemed to function spectacularly. And yet there was basically no indication of any impact on the screen. Even the people doing the color commentary for NASA TV were confused about that. We were all geared up for a climax that never came.

When you get excited, and expect something that doesn't come, you're disappointed. That's basically the definition of disappointment!! And I think there's no incompatibility between understanding that the mission was successful and still being disappointed about the lack of any sign that the impact happened during the live event.

--Emily

Seemingly, the PR impact has been greater (if in an unexpected way) then that of the physical event...didn't realize that the title of this thread would become a pun...

Maybe LCROSS was swallowed up by hundreds of meters of 'snow'.

...swallowed by snow or some other unexpected surface feature in the shadow was my first impression. Maybe the combination of cold and H2O condensation inside the shadowed crater created a cushion type textured surface that is very deep. Who knows?

The impact did occur and on target, but no fireworks. There has to be a logical explanation.

The simplest explanation, completely consistent with all the available data (once you strip off the hype) is that there were simply no significant volatiles at the impact site.

But shouldn't there have been "fireworks", even without ice?