Résumé / Abstract Seminaire_IAP
« A new face for early Mars [en français/in French] »

Sylvain Bouley
Laboratoire Géosciences, Université Paris-Sud XI (Orsay, France)

The Tharsis region is the largest volcanic complex on Mars and in the solar system. Young lava flows cover its surface (Amazonian, < 3Ga) but its growth started during the Noachian era (> 3.7 Ga). Its emplacement has induced a reorientation of the planet with respect to its spin axis (true polar wander - TPW), which is responsible for the present equatorial position of the volcanic province. It had been suggested that the Tharsis load on the lithosphere influenced the orientation of the Noachian/Early Hesperian (>3.5 Ga) valley networks1 and therefore that most of its topography was completed before their incision. Here, we calculate the rotational figure of Mars and its surface topography before Tharsis, when the spin-axis of the planet was controlled by the hemispheric dichotomy. We show that the observed directions of valley networks are also consistent with topographic gradients in this configuration and thus do not require the presence of the Tharsis load. Furthermore, their distribution along a small circle tilted with respect to the equator is found to correspond to a regular south tropical band in the pre-TPW geographic frame. Preferential accumulation of ice or water in a south tropical band is predicted by Early Mars climate model simulations applied to the pre-TPW topography. A late growth of Tharsis, contemporaneous with valley incision, argues for a causal link between volcanic outgassing and the stability of superficial liquid water. The inferred chronology, the topography of Mars before Tharsis and the existence of paleopoles, which have retained until today characteristic records of a glacial environment, offer new perspectives to examine Mars early geological history.
vendredi 8 décembre 2017 - 11:00
Amphithéâtre Henri Mineur, Institut d'Astrophysique de Paris
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