A few more updates in the last couple days or so regarding the evidence for past water on Mars. Previous evidence has continued to accumulate over the years, even for possible salty water still existing today in places. But three more recent findings add to this now as well.
First, in its brand-new exploration of Endeavour crater, the Opportunity rover has already found indications for past water activity, possibly hydrothermal. The first rock examined, Tisdale 2, showed very high concentrations of zinc and bromine, much more than previously seen before. On Earth, this usually means hot water moved around minerals, leaving deposits of zinc. This hydrothermal activity could be heated water or steam. But Opportunity still has a lot of work to do to sort out the details of this and other features of interest in this area, in particular the clays, which also point to water. The Spirit rover had already found strong evidence of hydorthermal activity at its landing site as well.
Second, the Mars Express orbiter has taken new photographs of an ancient delta in Eberswalde crater, which is thought to have been a lake a long time ago. Small feeder channels can also be seen, which would have filled the crater basin with water. This and other deltas, or what remains of them, are very similar to their counterparts on Earth.
Finally, a new report discusses evidence for a cold water ocean on ancient Mars. The long-running debate has usually been whether Mars was cold and dry or warm and wet in the past. This third option has gained more study recently, as it would help explain otherwise conflicting findings. There is a ton of evidence now that Mars was much wetter in the past, but still much debate over how warm it was, as some findings could be interpreted in different ways. The Martian ocean would have covered most of the northern lowlands, but new climatic and geophysical models suggest it would have been cold, not warm. Features around the edges, still visible, are consistent with glaciers. It would have been more like the polar seas, rather than the tropics, on Earth. So how does the evidence for lakes, rivers and hydrothermal regions fit into this? Still more questions than answers, it seems…