Is there liquid water on Mars?

National Geographic thinks that there is, based on a paper published by a NASA scientist and seven others. Before going into details, first a few facts about conditions on the surface. The maximum surface temperature is 20°C in direct sunlight, and the minimum is 140°C near the poles. The atmospheric pressure is less than 1% of that on Earth, at about 0.007 bar, or 600 pascals against 101.3 Kpa on Earth. I note that the paper, titled Spectral evidence for hydrated salts in recurring slope lineae on Mars, doesn't mention pressure at all, but does mention temperatures which might allow the presence of liquid water. Let's get this straight, despite media hype, the authors didn't find evidence for liquid water on Mars, but as their paper title says, hydrated salts. They hypothesise that there may be evidence for highly-saturated solutions of salts in the seasonal dark streaks observed on the slopes of Gale Crater. They say "These results strongly support the hypothesis that seasonal warm slopes are forming liquid water on contemporary Mars, but also say "The origin of water forming the RSL is not understood". RSL (Recurring slope lineae) are the "seasonal dark streaks" observed from orbiting satellites.

The strange thing (or is it?) is that several of the authors and other scientists seem to be far more certain of  compelling evidence in interviews than is evident in the published paper. As I said earlier, the paper mentions atmospheric pressure absolutely nowhere. At a pressure of ).007 bar, the boiling point of pure water is 2°C, and temperatures can reach 20°C on the observed crater slopes. Even strong salt solutions would evaporate water at temperatures well below 2°C, and ice (which would be pure water of course) would sublimate - evaporate without melting.

The jury is definitely out on this one, but the press and media are having a field day, presenting what I see from actually reading the paper to be a rather thin hypothesis as confirmed fact.