Oceans of the Solar System - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 231

such acid conditions precipitation of limestone would have been
inhibited. Therefore, much of the carbon dioxide on Mars, instead of
being converted into limestone rock as on Earth, simply drifted to the
top of the atmosphere and was lost to space.
So this was an environment that seems to have been both physi-
cally and chemically harsh. These short-lived, acid, salty oceans would
not have been ideal conditions for life—or at least for Earth-like life.
However, we know that some types of microbes can survive and adapt
to many different kinds of chemically extreme conditions. It remains
to be seen whether fossilized microbes, or even living ones, can be
found among the formerly water-rich provinces of Mars.
Where did the Mars ocean go to? In one interpretation it is still
there, frozen under a thin layer of sediment. 142 Radar soundings sug-
gest that layers of low-density material (such as ground ice) are present
beneath the northern plains (while any aquifers of liquid water, if
present, lie at deeper levels than those yet radar-sounded by the orbit-
ing satellites). When the ocean froze, though, some of the water would
have slowly sublimated—turned into vapour—and later would have
settled on the polar icecaps. Some of Mars's original store of water
would undoubtedly have drifted high into the thin atmosphere and
then been 'sputtered' away by the solar wind, to be carried off into
space. 143 Mars, after all, is considerably smaller than Earth, and so can
lock in its water supplies less effectively. Finally, its magnetic dynamo
switched off sometime in the first billion years, and so a protective
magnetosphere would have been lost.
Never the setting for a balmy tropical paradise, Mars's oceans will
not, perhaps, return until the dying days of the solar system. Then, the
Sun will give out a final burst of heat as it swells into a red giant star,
billions of years in the future. The ice caps and the remaining perma-
frost will melt and (briefly, once more) give rise to the last northern
ocean of that planet. Soon after, that too will be blown into space.