These people were trapped in a time -- a present-oriented time zone in which you never think of the future, you never think of the past.

CNN: Researcher: It's not bad apples, it's the barrel

If so, promising planets may have been sterilized by solar flares or frozen in the past, which wouldn't be reflected in present-day habitable-zone calculations.

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"The role of liquid water on Mars is of great importance for its habitability and this study using Mars Express describes a very large zone where groundwater was present for a long time, " said Olivier Witasse, a project scientist with ESA's Mars Express.

MSN: New proof that water existed underground on ancient Mars