mock y ▁surface ▁at ▁a ▁scale ▁of ▁about ▁ 1 0 – 2 0   km . ▁The ▁effect ▁of ▁rough ness ▁is ▁highlight ed ▁by ▁the ▁low ▁sun ▁ill um ination ▁angle . ▁Ord in arily , ▁rough ▁terra ▁material ▁would ▁be ▁sub div ided ▁and ▁mapped ▁as ▁individual ▁e ject a ▁blank ets ▁around ▁and ▁belonging ▁to ▁particular ▁cr aters . ▁In ▁this ▁eastern ▁region , ▁however , ▁the ▁closely ▁grouped ▁cr aters ▁have ▁about ▁the ▁same ▁age , ▁and ▁it ▁has ▁not ▁been ▁possible ▁to ▁distinguish ▁the ▁boundaries ▁between ▁their ▁apr ons ▁in ▁many ▁places . ▁ ▁Sm ooth ▁pla ins ▁material ▁covers ▁the ▁flo ors ▁of ▁numerous ▁cr aters ▁in ▁all ▁age ▁class ifications . ▁Its ▁surface ▁is ▁sc oured ▁by ▁secondary ▁cr aters ▁from ▁classes ▁c 4 ▁and ▁c 5 ▁cr aters ▁at ▁many ▁places ▁in ▁the ▁eastern ▁part ▁of ▁the ▁quad rangle ▁and , ▁within ▁the ▁cr ater ▁H omer ▁( 1 ° ▁S ., ▁ 3 7 ° ▁), ▁by ▁second aries ▁from ▁the ▁class ▁c 3 ▁cr aters ▁Tit ian ▁( 3 ° ▁S ., ▁ 4 2 ° ▁) ▁and ▁Hand el ▁( 4 ° ▁N ., ▁ 3 4 ° ▁). ▁Thus ▁the ▁smooth ▁pla ins ▁unit ▁may ▁have ▁a ▁relatively ▁wide ▁age ▁range . ▁Like ▁the ▁cr ater ed ▁pla ins , ▁it ▁exhib its ▁lo b ate ▁scar ps ▁and ▁few ▁mare - like ▁rid ges , ▁but ▁these ▁are ▁generally ▁smaller ▁than ▁those ▁of ▁the ▁cr ater ed ▁pla ins