So it’s pretty much agreed that Mars was once a wet planet, and most of the water was lost to space. However, I am unable to see why that is necessarily the case primarily for the same reason that Earth’s water hasn’t been lost to space (we would have lost our water if we relied only on gravity).
Atmospheres have what is called a “cold trap”, which is a spot in the middle where the atmosphere drops to low temperatures and causes water vapor to slow down/freeze and fall back to Earth. Mars should have had the same mechanism, but one that was even colder/better than the one we have here on Earth due to its distance from the Sun.
So here’s my theory, the water vapor wasn’t lost to space but frozen first. Then over millions of years it has been buried over by the massive planet wide dust storms Mars is known for. This in turn would provide alternative explanations for why the northern hemisphere of the planet is so smooth as well as why only the Southern Hemisphere retains any magnetic rocks (the diamagnetic properties of water prevented the magnetism retention of the northern hemisphere that southern possesses).
I realize this is probably not likely, but what I would like to know is why? Are there any sources that can disprove this theory? I have been unable to locate any.