The conjecture I've heard speculates that billions of years ago. Yes... not millions... but BILLIONS of years ago, when mars was significantly younger, the atmosphere may have been a lot thicker than that it is today. More atmospheric pressure in turn would have allowed liquid water to remain on the surface indefinitely.
I believe it has been speculated that perhaps Mars had at one time a molten core, which in turn generated a planetary magnetic field. It is theorized that due to the shielding effect of the magnetic field the atmosphere, to a large extent, was protected from being blown away due to the harsh effects of the sun's solar wind. After the core cooled and the magnetic field dissipated there was no magnetic shield left to protect Mar's tenuous atmosphere. Over millions of years the atmosphere was gradually blown away. At present, the most prosaic theory I've heard as to whether life may have at one time flourished on the surface of Mars is that if it HAD flourished it must have done so a very long time ago. Probably more than a billion years ago, or longer. Of course, there may still be traces of bacterial life that may have managed to hang on underground where pockets of liquid water and life sustaining minerals may still exist in relative abundance. We'll just have to go there and look for ourselves! I'm game! Maybe we might be in for a big surprise. Regards Steven Vincent Johnson www.OrionWorks.com www.zazzle.com/orionworks
