A brief inquiry regarding Martian history

[Apollo7]

Something has been bothering me about Mars, of late and hopefully you guys can set me straight as you have done so in the past.

We all hear how Mars was -once- wet, warm and possibly for a time in the ancient past harbored the elements required for life to develop. That is all well and good and certainly makes for interesting speculation, however.

Mars has about 10% the Mass of the Earth and about 38% of the surface gravity. In addtion 3 billion years+ ago, when Mars' wet period would have been in effect it would have had to have posessed a substancial atmosphere and a large greenhouse effect. Nowadays the greenhouse effect on Mars raises the surface temperature only about 1K. Back "in the day" as it were, however, The Sun would have been less luminous and Mars would have been even further outside of the comfort zone, and thus would require an even more effecient greenhouse effect to stay warm.

Here is my inquiry, how is this possible? Even today Mars is not within the CZ of the Sun, and wont be for another 2 billion years or so, that being said, wouldn't Mars have required a think atmosphere filled with Methane, Water Vapor and Carbon Dioxide to retain the conditions necessary for liquid water at a time when the Sun would have been less brilliant than it is today. And further, would not Mars have required great ammounts of volcanic outgassing to sustain that primordial atmosphere and to keep the surface warm for a relatively long period of time? Considering all this, where has the atmosphere gone, and if it was lost due to weak gravitation and the end of vulcanism, can we access how thick it was in the past? Anyway I hope you guys can help me out here, Cheers.

[Eburacum]

This may be a little out of date; but read this; you are essentially correct.

http://www.atmos.washington.edu/~davidc ... sAtmos.pdf