Jeff isn't entirely neutral in this. He is one of the co-authors on the Hellas paper and others that we have produced in collaboration at USGS.

This is actually part of my strategy for changing thinking about water on Mars. So long as the models were 100% water-based, they were unrealistic for Mars. To be fair, several authors had explored soda-pop type models for Mars subsurface but these models weren't really going anywhere new.

What I've injected into the scene is a new class of end-member models based entirely or largely on CO2.

We're now beginning quite a healthy debate about where on the spectrum we should be for a useful model of Mars.

I argue that CO2 alone can explain almost everything on Mars. My opponents, with great glee and satisfaction, drag me out of that position to somewhere around 50:50 and think that they have "won", but in fact, I have acheived my objective of getting them out of a 100% water model.

After that, science and informed debate will resolve exactl what range of models are useful for Mars, but 100% water is not one of those, IMHO...