images 30 years ago, it was startling to see these whitish craters and ejecta against such a dark Acidalia plain.

But I accepted the standard interpretation of them as impact craters -- why not? There didn't seem to be any likely alternatives at the time.

Many more images of these formations were available thanks to the Viking Orbiters, and as I saw them in better resolution and detail, I began to question the conventional interpretation. I thought, well, these might be impact craters, but they really didn't look like any on the Moon, say, or other obvious impact craters on Mars. There were a number of attempts at conventional explanation, including the one I eventually accepted more or less: that they were indeed impact craters, but that they were formed in icy terrain, and their "softness" (and whiteness) was due to all that excavated ice. At the time, the notion that they were NOT impact craters at all, but instead might be some kind of monstrous vents, simply wasn't even discussed. (Well, except in private communications.)

When closeups from the Mars Global Surveyor became available a few years ago, I expected a vigorous discussion of the origin of these formations, but there was none. Malin stuck rigidly with the Mariner 9-era interpretation as impact craters. (In fact, Malin's rigidity on the issue borders on ludicrous, but I digress.)

The literature showed almost no questioning of crater origins, and as you've shown, even papers that do bring up the possibility of alternate origins for circular formations mention only one or two examples and do not extend those examples beyond the ones under discussion.

The absence of much discussion about alternative origins is troubling, especially given the enormous number of examples we can now consider.

I don't know the origin of this example. It could be an impact structure. Or, it could have originated through impact and been modified by venting from the subsurface, or have been modified by external erosive forces. Or it could have originated as a vent and not have any relationship to impact at all.

I'd like to see some really vigorous discussion about these or other alternatives, but it isn't happening. Instead, there's a lot of rigidity of assumption, a lot of avoidance of the topic, and the occasional hostility and insult of folks who ask questions or offer alternative viewpoints.

No doubt the time will come when the paradigm has to shift, and our understanding of Mars will undergo profound reconsideration. That time isn't quite yet, but it will come. No doubt.

Meanwhile, we do what we can to tweak the complacent, urge wide-ranging consideration, or just speculate wildly about what could be and once was.

Thanks for your efforts toward understanding.

Cheers, BFelix