Why is io the only solid surface in the solar system that is completely devoid of impact craters?

the pacific ocean just sreach up it and youll have our answer i had this question before

northern hill zone (nhz)

western himalayan regions of j& k (except jammu and kathua distt.); h.p. (except una and paonta valley); uttaranchal (except tarai area); sikkim and hills of west bengal and n.e. states

north western plains zone (nwpz)

punjab, haryana, delhi, rajasthan (except kota and udaipur divisions) and western up (except jhansi division), parts of j& k (jammu and kathua distt.) and parts of hp (una dist. and paonta valley) and uttaranchal (tarai region)