Appears to be a ring shaped object, hollow sphere, or "pipe"-like feature. In fact it is just a semi-circular impression made in the sand by the Moessbauer spectrometer -- one of the rover's instruments (to look at soil physics/chemistry). So a perfectly rational explanation. Microscopic Imager Non-linearized Full frame EDR acquired on Sol 65 of Spirit's mission to Gusev Crater at approximately at approximately 11:20:02 Mars local solar time, Microscopic Imager dust cover commanded to be OPEN.