At our daily afternoon coffee late last week, we were discussing the new images fromNASA's now-defunct Mars Global Surveyor. These pictures show changes in the gullies in a crater, suggesting that liquid water has flowed on the surface of Mars within the last few years! This would mean that Mars must have liquid water today in underground lakes or caverns, and that this water sometimes escapes to the surface, where it quickly evaporates.
Few of us here, and certainly not me, are planetary scientists, so it is hard for us to judge the data for ourselves. Must the changes in this crater be due to liquid water? I can't say. But it is fun to debate the implications. On Earth, liquid water = life. Did Mars ever have life? Could it have life now? Can living things survive in this water, which is probably very acidic and extremely salty? I don't know the answers to that, either. But it is fun to speculate! Now the question becomes how to find the water and search for life without contaminating Mars or a soil sample with bacteria from Earth. Easy enough to say, but hard to do! Do we need a lander that can traverse these craters? If the crater is full of dust, how can a lander safely land and get partway up the crater wall without slipping? How can we completely sterilize a spacecraft that, by necessity, must sit on the launch pad in Earth's weather and launch through Earth's atmosphere, which is teeming with all forms of life?