This is a mosaic of Viking images of most of the Argyre impact basin, which is approximately 1100 kilometers in diameter. The basin is at the upper left and is surrounded by a ring of rough debris that was ejected from the basin. Argyre formed when an asteroid or comet roughly 50 kilometers across impacted Mars. Large basins such as Argyre are believed to have formed very early in the history of Mars, about 4 billion years ago.
Viking Orbiter mosaic P-17022, viewed looking east