re: Why couldn't the disappearing white matter be CO2?
Yes, we're all waiting for the oven's results. CO2 ice has been number one in my mind too, but maybe that's because we're so close to the cap which is mostly made up the stuff. Still, I'm hopefull that there's buried H2O ice beneath this area. We'll see.
I hope they took into account that martian soil could have settled, even out of place by low winds. Come to think of it, I took the Martian weather into account as well.
Just some thoughts.