Hi Rob,

Yes, since the gravity of the moon is lower, the particles would be launched higher, and fall more slowly. The large chunks of debris would travel farther than they would on earth (owing to the reduced gravity and air resistance), but the smaller dust particles wouldn't (owing to the lack of an atmosphere to be suspended in). On earth, the larger chunks of debris would fall relatively close to the impact site, while the wind-born dust would drift around the globe. On the moon, both the large chunks and the dust would travel exactly the same distance.

Some simple equations, going entirely from memory: gravitational acceleration on the moon is .16 of earth -- approx. 1.57 m/s^2. Impacts on the earth-facing side of the moon are likely to be slowed a bit by the pull of earth, so let's say that they come in at 5 km/s, and kick out debris at half that velocity. The debris that's ejected at 45 degrees will travel the farthest, so that look at that. Interestingly, the size of the impactor shouldn't effect these numbers at all -- that'll only add to the quantity of debris, not its ballistic properties. Only the velocity of the impactor is relavent in this case.

Here's the real basic numbers: How long would the debris be in flight?

z = 2,500*sin(45)*t - 1/2*1.57*t^2
0 = 1,768*t - .785*t^2
-1768 = -.785*t
t = 2252 sec. (38 minutes)

How high would the debris cloud reach?

z = 1768*1126 - .785*1126^2
z = 1990768 - 99583
z = 1,891,185 m (1182 miles)

And how far would the dust be disperssed?

x = 1768 * 2252
x = 3,981,536 m (2488 miles) (not taking the curverature of the moon's surface into account, which would actually increase the distance significantly.)

So yeah, it turns out that an impact would spread the regolith around a long ways, owing to the moon's reduced gravity. But I'm not sure that this would make the debris cloud any easier to be spot. A small impact would produce a relatively minimal amount of debris, quickly dispersing over a very large area. For an impact large enough to produce a debris cloud dense enough to be visible, the flash of light would probably be more than impressive enough to capture everyone's attention...

gotta run,

Nathan.