Persistent or repeated surface habitability on Mars during the Late Hesperian - Amazonian

TL;DR

This study uses crater analysis to show that alluvial fan deposits on Mars persisted for over 100 million years, indicating long-lasting habitable surface conditions during the Late Hesperian to Amazonian periods.

Contribution

It provides the first robust lower bound of 100-300 million years on the duration of alluvial fan formation on Mars, suggesting sustained habitable conditions.

Findings

Alluvial fan deposits record habitable surface conditions lasting over 100 million years.

Crater analysis indicates a minimum of 100-300 million years for fan formation.

The results rule out brief climate anomalies as the sole cause of fan formation.

Abstract

Large alluvial fan deposits on Mars record relatively recent habitable surface conditions ($\lesssim$3.5 Ga, Late Hesperian - Amazonian). We find net sedimentation rate <(4-8) {\mu}m/yr in the alluvial-fan deposits, using the frequency of craters that are interbedded with alluvial-fan deposits as a fluvial-process chronometer. Considering only the observed interbedded craters sets a lower bound of >20 Myr on the total time interval spanned by alluvial-fan aggradation, >10^3-fold longer than previous lower limits. A more realistic approach that corrects for craters fully entombed in the fan deposits raises the lower bound to >(100-300) Myr. Several factors not included in our calculations would further increase the lower bound. The lower bound rules out fan-formation by a brief climate anomaly. Therefore, during the Late Hesperian - Amazonian on Mars, persistent or repeated processes permitted habitable surface conditions.