It's crucial to understand how water actually behaves at the surface of Mars. Since the presence of water (ice) very nearly at the surface, very nearly everywhere, and in substantial volumes (in permafrost and possibly discreet deposits) is no longer being widely disputed, it's even more important to understand how water behaves.

The Ice Towers of Hellas is a very dramatic proposal. And why not? Sometimes drama is necessary. ;-)

The idea that water could be flowing now, somehow carving gullies on the slopes of crater and cliff, or causing dark stains running down into valleys was considered extravagant nonsense not so very long ago.

A question, of course, is why there should be fumaroles spewing water in Hellas at all. There is little or no sign of current or recent volcanism in Hellas, although many volcanic features are found around the basin. Or are there signs that I have missed? It would not be the first time!

Seems to me we should be leery of relying on "average surface temperatures" as a foundation to accurately or adequately describe the behaviour of water on the Martian surface. The "average" is almost always lower than 279K almost everywhere on Mars. Variations away from that average can be substantial, all within a single day, rising considerably higher than 279K and falling much lower. Unless the behaviour of water at all stages of likely daily and annual temperature and pressure variations is carefully studied, assertions or conclusions based on "average surface temperatures" will likely be in error, perhaps grossly so.

What argument is used to claim that no active vents or fumaroles have been discovered anywhere on Mars? There are hundreds -- indeed, thousands -- of point sources of higher temperatures visible in THEMIS nighttime IR images. Have they all been definitely determined to be... something else?

More study, more study, more study!

Cheers, BRFelix