The apparent reason for this is that the surface is so porous that an impacting space rock causes little ejecta, material blasted out of the collision site and is scattered all around.

• 形成这种情况的一个明显原因就是土卫七表面如此千疮百孔，撞击到上面的太空岩石不会激起内部物质从撞击地点飞散到周围。