<blockquote><font class="small">In reply to:</font><hr /><p>looks like it really is not my day ... review of "shadow" hypothesis in two pictures does not reveal significant difference, so "bloom" hypothesis remains reasonable ...<p><hr /></p></p></blockquote><br /><br />Don't feel too bad. Everybody comes up with hypotheses that don't stand up. It's part of the normal process of looking at the world, studying it, questioning what you see, and trying to work out what's out there. This object has been identified as part of Opportunity's heat shield; it's visible in multiple pictures. (It's not the whole heat shield, obviously. It's just a fragment.) But you didn't neccesarily know that. If you were a total pathetic space geek like me, poring over dozens of these pictures just for the hell of it, you might have recognized it. But if you have a life outside of JPL websites, you probably wouldn't. <img src="/images/icons/wink.gif" /><br /><br />(And yes, I really did recognize that pic the moment I saw it. I know which raw image it's taken from.)<br /><br />The "bloom" phenomenon is not unique to Opportunity, by the way. It's a deficiency in all CCD imagers, and a consequence of their design. Unfortunately, all imaging devices have limitations, and this is probably one of the most significant from CCDs. You can compare it to overexposing 35mm film with your regular still camera. Have you noticed how an overexposed object will seem to glow on the final print? It wasn't glowing; it's just that the film emulsion bled a bit, giving the overexposed object a blurred, ethereal appearance. (If you're better at photography than me, this can be very pretty. My brother does it on purpose to make pretty pictures.) CCDs are digital, so you don't get a gentle blur. And they're electronic, so instead of photochemicals leaking into other parts of the emulsion, you get electrons spilling into other pixels on the grid. Generally, this will happen along one axis only -- either up and down <div class="Discussion_UserSignature"> <p> </p><p><font color="#666699"><em>"People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff."</em> -- The Tenth Doctor, "Blink"</font></p> </div>