Just a quick follow-up to the previous post about the odd “bubbles” seen by the Curiosity rover on Mars. There is now a nice new Mastcam image (sol 122) showing one of these features close-up. They do look like former bubble-shaped domes on the bedrock which have since mostly eroded, leaving behind little ring-shaped “walls.” There are quite a few in this area, generally about a few centimetres across or so. What caused them? Bubbling mud? Venting gas? Something else? Another “curious” little mystery!