The real question we're trying to answer is: "has that ice melted", because liquid water in contact with soil may provide us with a habitable environment. For microbes, the word 'habitable' means you have liquid water, complex organic molecules of the type our bodies are made of - proteins, amino acids and so on - and it also means you have energy sources.

One of the interesting questions is why organic molecules weren't found on the surface of Mars by Viking [Nasa Mars mission from the 1970s]. The answer is we think there is a mechanism which can destroy organic molecules on Mars. This mechanism might not be operating in the polar regions because water and ice can decompose the oxidants that destroy the organics.