Re:Hubert Reeves
I once asked Hubert Reeves (august 96 it must have been) a question: why would there have been a thicker atmosphere in the very far past and much less now, knowing that Mars has always had the mass it has and was always as far from the sun it is now?
His answer was that in the past, comets were raining on Mars and have increased its atmospheric density. Once fewer comets started to fall, the atmosphere escaped due to its lower gravity.
I found it an interesting answer but still, Mars never had a larger mass than it has now, so...
Raoul