They probably were in a similar orbit and made a soft landing. Some may
have been thrown up from Eros by an impact and have fallen down again.
I imagine that dust will be more easily thrown up from Eros than
somewhat larger objects. This does not seem all that mysterious to me.
Neither do I think that the
volume of matter lost to space would always be greater than the
volume of matter created by the impact. Most impacts will be from
smaller particles like dust and protons and helium and I must assume
that at least some asteroids gain mass because of it.
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