Curious bright streaks on Mercury's surface, doodled on its craters and slopes, are probably a sign of very recent geological activity, according to new models. The findings suggest that Mercury is far from being 'dead' or dull, as astronomers once supposed. Related: A Fortune of Hidden Diamonds Could Be Concealed Inside MercuryUntil recently, scientists had catalogued only a handful of Mercury's bright streaks, known formally as lineae. Their findings reveal that the long bright lines on Mercury's surface tend to cluster on the sun-facing slopes of its craters, although they don't always appear to emanate from hollows. If Mercury's surface is still active, we should get a closer glimpse soon.