Landers don't impact hard - they fire rocket engines down, which may be much more efficient at kicking up dust than an impact.
(I still think this is overblowing the problem, because any lander that causes this big of an ejecta problem would also badly damage itself. All the designs will put a LOT of engineering work into minimizing debris, eg Starship putting separate landing engines high up on the vehicle.)
> because any lander that causes this big of an ejecta problem would also badly damage itself
Not necessarily because the relative speeds will be very slow. Not so in low lunar orbit, where an orbiting spacecraft will slam into the ejecta curtain at >1 km/s.
The paper estimates that if there's LLO debris, it'll be starting out with about 1.6km/s of surface-relative velocity. Not something you want to get even a small percentage of on your landing gear.
The ejecta would go out to the side and not harm the lander. I'm just amazed that the ejecta is being thrown hard enough to be a threat at orbital altitude.
(I still think this is overblowing the problem, because any lander that causes this big of an ejecta problem would also badly damage itself. All the designs will put a LOT of engineering work into minimizing debris, eg Starship putting separate landing engines high up on the vehicle.)