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The Dawn spacecraft observed the presence of dark material, which in turnproved to be associated with OH and H-rich material, on the surface of Vesta.The source of this dark material has been identified with the low albedoasteroids, but it is still a matter of debate whether the delivery of the darkmaterial is associated with a few large impact events, to micrometeorites or tothe continuous, secular flux of impactors on Vesta. The continuous fluxscenario predicts that a significant fraction of the exogenous materialaccreted by Vesta should be due to non-dark impactors likely analogous toordinary chondrites, which instead represent only a minor contaminant in theHED meteorites. We explored the continuous flux scenario and its implicationsfor the composition of the vestan regolith, taking advantage of the data fromthe Dawn mission and the HED meteorites. We used our model to show that thestochastic events scenario and the micrometeoritic flux scenario are naturalconsequences of the continuous flux scenario. We then used the model toestimate the amounts of dark and hydroxylate materials delivered on Vesta sincethe LHB and we showed how our results match well with the values estimated bythe Dawn mission. We used our model to assess the amount of Fe and siderophileelements that the continuous flux of impactors would mix in the vestanregolith: concerning the siderophile elements, we focused our attention on therole of Ni. The results are in agreement with the data available on the Fe andNi content of the HED meteorites and can be used as a reference frame in futurestudies of the data from the Dawn mission and of the HED meteorites. Our modelcannot yet provide an answer to the fate of the missing non-carbonaceouscontaminants, but we discuss possible reasons for this discrepancy.

The contamination of the surface of Vesta by impacts and the delivery of the dark material