Is it ice? Part 2

Pull up your trousers: Is it ice?
A few sols back (a 'sol' is a Martian day) the robotic arm on Phoenix dug a trench which uncovered some white material. There was excitement about ice but nothing could be said for sure until more analysis. Note that in this image the bright white areas at the top of the trench are difficult to interpret. It all depends on how you set the contrast. I would rather draw your attention to the light coloured 'pebbles' in the shadow at the bottom left.

If the white stuff was ice then, exposed to the thin Martian atmosphere and warmed by the Sun, it would sublimate. That is, the ice would not melt as it does back home, but evaporate directly from solid to gas with no intermediate liquid phase. It's the same behavior we see on Earth with dry ice (frozen carbon dioxide).

In the meantime a soil sample delivered to one of the analyser ovens showed no trace of water. Emily Lakdawalla explains:


No surprise there then. If there had been ice in the sample it would have evaporated away before reaching the oven.

So what has happened in the trench, 4 sols since the first photo?


This is not phototrickery. It's real.

Some folks are saying this is proof of ice, even the Phoenix team themselves. Others, such as Emily Lakdawalla, are more cautious.

I'm still hesitating to say I'm fully convinced. Not that I think alien pixies flew off with those lumps during the darksol, I just want to see a water signal in the gas analyser.