The origin and timing of fluvial activity at Eberswalde crater, Mars
Résumé
The fan deposit in Eberswalde crater has been interpreted as strong evidence for sustained liquid water onearly Mars with a paleolake formed during the Noachian period (>3.7 Gy). This location became a key regionfor understanding the Mars paleo-environment. Eberswalde crater is located 50 km north of the rim of the150 km diameter crater Holden. Stratigraphic relationships and chronology obtained using recent MarsExpress High Resolution Stereo Camera and Mars Reconnaissance Orbiter Context Camera images showthat Eberswalde fluvial activity crosscuts Holden ejecta and thus postdates Holden crater,whose formationage is estimated from crater counts as Late Hesperian (3.5 Gy, depending on models). Fluvial modelingshows that short term activity (over several years to hundreds of years) involving dense flows (with sediment:water ratio between 0.01 and 0.3) may be as good an explanation of the fluvial landforms as diluteflow over longer durations. Modeling of the thermal effect of the Holden impact in the Eberswaldewatershed is used to evaluate its potential role in aqueous activity. The relative timing of the Holden impactand Eberswalde’s fan is a constraint for future studies about the origin of these landforms. Holden ejectaform a weak and porous substrate, which may be easy to erode by fluvial incision. In a cold climate scenario,impact heating could have produced runoff by melting snow or ground ice. Any attempt to model fluvialactivity at Eberswalde should take into account that it may have formed as late as in the Late Hesperian,after the great majority of valley network formation and aqueous mineralization on Mars. This suggeststhat hypotheses for fan formation at Eberswalde by transient and/or localized processes (i.e. impact,volcanism, unusual orbital forcing) should be considered on a par with globally warmer climate.