The Evolution of the Martian Hydrosphere: Implications for the Fate
of a Primordial Ocean and the Current State of the Northern Plains
Icarus, (2001)Аннотация
In this paper we consider the hydraulic and thermal conditions
that gave rise to the elevated source regions of the Late Hesperian
outflow channels and explore their implications for the evolution of
the Martian hydrosphere. We find that if the outflow channel flood-
waters were derived from a subpermafrost aquifer, then it implies
that, throughout the planet’s first billion years of evolution, as much
as one third of its surface was covered by standing bodies of water
and ice. Following the development of the global dichotomy, the
bulk of this water would have existed as an ice-covered ocean in the
northern plains. We demonstrate that the progressive crustal assim-
ilation of this early surface reservoir of H2 O (punctuated by possible
episodes of less extensive flooding) was a natural consequence of the
planet’s subsequent climatic and geothermal evolution—potentially
cycling the equivalent of a km-deep global ocean of water through
the atmosphere and subsurface every ∼109 years. In response to
the long-term decline in planetary heat flow, the progressive cold-
trapping of H2 O into the growing cryosphere is expected to have
significantly depleted the original inventory of groundwater—a de-
velopment that could well explain the apparent decline in outflow
channel activity observed during the Amazonian. Although primar-
ily a theoretical analysis, our findings appear remarkably consistent
with the geomorphic and topographic evidence that Mars once pos-
sessed a primordial ocean and that a substantial relic of that body
continues to survive as massive ice deposits within the northern
plains. Confirmation of the presence of such deposits, combined
with the potential detection of a global-scale groundwater system,
would provide persuasive support for the validity of this analysis.