Posidonius - 99 km wide, 2.3 km deep
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Posidonius has steep sides with hills and cracks on its floor. This large crater lies on the eastern "shore" of the Sea of Serenity. It is tilted down towards the west. To the left of Posidonius you can see the long and sinuous ridge known as Dorsa Smirnov. The wrinkle ridge runs for 134 km north to south.
Image: February 22, 2007