# 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.

## Key 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.

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Source: https://tomesphere.com/paper/1703.06386