1

When Did Mars Become Bipolar?: An Analysis Of The Key Factors In
The Late Noachian-Amazonian Climate Transition From An
Altitude-Dominant Temperature Distribution (Add) To A Latitudedominant Distribution (Ldd).
James W. Head1, Robin D. Wordsworth2 And James L. Fastook3, 1brown University, Providence, Ri 02912 Usa,
2
Harvard University, Cambridge, Ma 02138 Usa, 3university Of Maine, Orono, Me 04469 Usa
(James_head@Brown.Edu).
Introduction: The History Of The Atmosphere And Climate Of Mars (Fig. 1) Is One Of The Major Current Outstanding Question In Planetary Science [1-2]. Mars Today
Has An ~6.5 Mbar Co2-Dominant Atmosphere, And A Hypothermal (~210k Mat), Hyperarid Polar Desert Climate
(10-20 Precipitable Microns Of H2o In The Atmosphere)
[3], With Surface Water Sequestered In The Polar Caps [4].
Yet In Earlier History (Noachian, N), There Is Strong Evidence For Sustained Periods Of Abundant Surface Liquid
Water, Both Flowing (Valley Networks) And Standing
(Open-Closed Basin Lakes, Oceans) (Fig. 1), Correspondingly Higher Atmospheric Pressure (Patm ~1-2 Bar?) [5],
And Surface Temperatures (Mat In Excess Of 273k) [6-7]
(Fig. 2).
Two General Classes Of Models Have Been Proposed To
Account For These Observations (Fig 2): ‘Warm And Wet’