LONG TERM EVOLUTION OF EARLY MARTIAN CLIMATE – VALLEY
NETWORK FORMATION BY WARM OR COOL CLIMATE CONDITIONS
A. Kamada1 (ari_kmd@pat.gp.tohoku.ac.jp), T. Kuroda1,2, T. Kodama3, Y. Kasaba4, and N. Terada1
1
Department of Geophysics, Graduate School of Science, Tohoku University, Sendai, Japan. 2Division for the
Establishment of Frontier Sciences, Organization for Advanced Studies, Tohoku University, Sendai, Japan.
3
Komaba Institute for Science, Graduate School of Arts and Science, University of Tokyo, Tokyo, Japan.
4
Planetary Plasma and Atmospheric Research Center, Tohoku University, Sendai, Japan.

Introduction:
Although present-day Mars is cold and dry with a
low pressure of CO2 atmosphere and little amount
of surface and subsurface H2O ice, decades of
geochemical and geological observations have
revealed that the atmospheric environment on early
Mars was quite different from that of Mars today.
Early Martian terrains were carved by numerous
networks of valleys, indicating evidence that
prolonged liquid water activity sculpted the ancient
surface of Mars during the late Noachian and the
early Hesperian (3.85–3.6 Ga). However,
controversy remains over the source of liquid water,
that is, rainfall [1-4] and snow/ice melting [5-9].
Depending on which scenario of the water source is
chosen, the climate condition of early Mars would
be quite different.

Method:
To explore the best climate scenario of early Mars,
we performed several series of climate simulation
of early Mars for long timescale by a combination
of global climate model (PMGCM, Paleo-Mars
Global Climate Model), global river model (CRIS,
Catchment-based RIver Simulator) [10,11], and
global ice sheet model (ALICE, Accumulation and
ablation of Large-scale ICE-sheets with dynamics
and thermodynamics) (see Figure 1). We assumed a
CO2/H2O/H2 atmosphere with surface pressures of
between 1 bar and 2 bar, H2 mixing ratios of
between 0% and 6%, and obliquity of 40°.
Geothermal heat flux was set to 55 mW m-2, which
are representative of the late Noachian and the early
Hesperian [12,13]. We defined the existence of a
northern ocean and lakes in our model with the
amount of corresponding to about 500 m global
equivalent layer (GEL) at the initial state, and
implemented a pre-True Polar Wander topography
to investigate the global water cycle of early Mars
before late Tharsis formation [14] (see Figure 2).
We iterated the runs of the ALICE and
PMGCM–CRIS coupled model several times over
the course of 105 Mars years to obtain the
long–term equilibrium states for each condition of

surface pressure and H2 mixing ratio.

Figure 1. Schematic diagram of global river model
CRIS [11] (top), and global ice sheet model ALICE
(bottom).

Figure 2. Pre-True Polar Wander topography and
the initial distribution of ocean/lakes (in aqua)
assumed in this study [11].

Results:
We showed that climate on early Mars is classified

into three conditions. First, when surface pressure
and H2 mixing ratio were both high, climate on
early Mars would be “warm and semi–arid”,
meaning that global averaged temperature was
above 273 K, and prolonged rainfall–fed river
systems carved valleys on southern low to middle
latitudes where the majority of valley networks are
observed (see Figure 3). These valleys were formed
within a relatively short geological timescale (~104
Mars years), which agrees with previous geological
studies of valley network formation timescales
(104–106 Mars years) [15-17]. Second, when
surface pressure and H2 mixing ratio were both
middle, climate on early Mars would be “cool and
wet”, meaning that global averaged temperature
was slightly below 273 K, but temperate–based ice
sheets became widespread (see Figure 4).
Subglacial meltwater–fed river systems carved
valleys on southern low to middle latitudes within a
relatively long geological timescale (~105 Mars
years) than “warm and semi–arid” case. Finally,
when surface pressure and H2 mixing ratio were
both low, climate on early Mars would be “cold and
icy”, meaning that global averaged temperature was
much below 273 K, and cold–based ice sheets
became widespread. In both cases of “warm and
semi–arid” and “cool and wet”, our river model
CRIS produced valleys whose distributions agreed
with more than half of the observed ones. Many
river systems in the Noachian highlands are likely
to have originated from either rainfall or subglacial
meltwater. However, in just case of “cold and icy”
scenario, there was almost no apparent surface
liquid water activity, which is contradictory to
observations.

Conclusions:
From our calculations and geological constraints for
coexistence of fluvial and subglacial runoff systems,
we conclude that early Martian climate could have
experienced both “warm and semi–arid” and “cool
and wet” situations depending on atmospheric
amount of H2. However, some parts of modelled
runoffs are discrepant with observed valley
networks such as Margaritifer Terra. There is still a
possibility that several valleys were produced by
short-lived climatic warming, possibly through an
increase in atmospheric greenhouse gas resulting
from volcanism and meteorite events.

Acknowledgements:
This work is supported by the Japan Society for the
Promotion of Science (JSPS) KAKENHI Grant
Numbers JP19H00707 and JP21K13975, and the

Astrobiology Center Program of National Institutes
of Natural Sciences (Grant Numbers AB312005 and
AB031014). The model runs have been performed
with FUJITSU PRIMERGY CX 2550/2560 M4
(ITO) system at the Research Institute for
Information Technology, Kyushu University.

Figure 3. Annual averaged runoff (mm sol-1) with a
H2 mixing ratio of 6% and surface pressure of 2 bar.
Gray contours denote the topography, remapped to
the present Martian topography with sea level of
-2.54 km.

Figure 4. Simulated global distributions of glacial
thickness (m) in the equilibrium state with a H2
mixing ratio of 3% and surface pressure of 2 bar.
Gray contours denote the topography, remapped to
the present Martian topography with sea level of
-2.54 km.

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