Regolith blast-out velocity?

[AstroBrant]

I've discussed this with a couple of YouTubers. What might the maximum speed of regolith particles be as the LMs landed?

I've gotten that the exhaust gas speed near touchdown was 2700 - 2800 m/s. I was wondering if there was a chance that some particles actually achieved lunar orbit or maybe even escape velocity. But I have nothing like the skill in physics to determine this. One would have to know how to calculate how fast particles could be ejected under those circumstances. Then the vertical angle needs to be considered. I realize this may be beyond anyone's capability here, but it's worth a try.

Any kind of estimate would be appreciated. Maximum speed, average speed, probable speed range, anything like that. Even just your opinion.

To Admin., if I'm being rude to ask a question that is potentially so difficult, or possibly even unsolvable, please PM me.

[Bob B.]

The following article says between 0.6 and 1.5 miles per second (about 1000-2400 m/s).

http://www.space.com/4956-lunar-landers-sandblasted-moon.html

[JayUtah]

Reasonably you can't expect entrained particles to exceed the fluid velocity.  The deflected velocity tends to have 70-80 percent of the mean stream velocity of the engine flow, the majority of it angled a few degrees upward from the horizontal.

[ka9q]

And the moon's escape velocity is 2380 m/s, so at least some of those entrained particles could escape. Many more could land at a great distance.

It's unlikely any would actually orbit the moon. It's impossible to put something into orbit with a single impulse from the surface. Even if any did reach orbit, lunar orbits are notoriously unstable.

[AstroBrant]

Reasonably you can't expect entrained particles to exceed the fluid velocity. 

Right. I would not expect that. I also have an intuition that the density of the exhaust gas might have an effect. It would seem that the gas right before touchdown would be pretty thin.

[AstroBrant]

And the moon's escape velocity is 2380 m/s, so at least some of those entrained particles could escape. Many more could land at a great distance.

It's unlikely any would actually orbit the moon. It's impossible to put something into orbit with a single impulse from the surface. Even if any did reach orbit, lunar orbits are notoriously unstable.

I remember discussing that in my previous conversations. It would seem that in an ideal situation a particle could return close to where it was launched. But I'm aware that the moon's gravity varies from location to location, which would alter trajectories. I really didn't expect particles to establish a stable orbit, so I shouldn't have said that. But I was wondering how many would make it all the way around, and, dare I speculate, possibly land somewhere near the LM during an EVA.

[Bob B.]

But I was wondering how many would make it all the way around, and, dare I speculate, possibly land somewhere near the LM during an EVA.

Don't forget that the Moon is rotating.  Even if some of the dust did return to its starting point, it would land where the LM was two hours ago.  The LM would be about 30 kilometers to the east of that spot.