The Pace of Fluvial Meanders on Mars and Implications for the Western Delta Deposits of Jezero Crater

Abstract

Although there is little doubt that rivers once flowed on Mars' surface, how sustained and frequent their flows were remains enigmatic. Understanding the hydrology of early Mars, nonetheless, is a prerequisite to resolving the planet's climate history and the astrobiological potential of various ancient putative ecosystems. In 2021, NASA's Perseverance rover will attempt to land near ancient fluviodeltaic deposits in Jezero crater. Deltas offer enhanced organic-matter burial and preservation on Earth but translating this notion to early Martian environments remains speculative in the absence of information on flow intermittency and sedimentation rates. Here we develop a new model to infer the lateral migration rate of Martian river meanders, which, combined with orbiter-based observations of the fluviodeltaic deposits at Jezero crater, allows us to determine a minimum timescale for the formation of its delta. We then independently constrain the total duration of delta formation, including dry spells. Our best estimates suggest that delta formation spanned~19-37 years over a total duration of~380,000 years, i.e., that rivers flowed for a minimum~1 sol/15-30 Martian years and conceivably more frequently, but uncertainties on total duration are large. Despite a possibly arid climate, predicted sedimentation rates are high, suggesting a rapid burial of putative organics in distal deposits. Altogether, our results support Jezero crater's potential as a prime target to look for ancient Martian life and acquire samples to return to Earth. Any discrepancies between our predictions of the deposits' grain-to-bedform-scale architecture and future rover observations will shed critical light onto Mars' early surface environments. Plain Language Summary Rivers once flowed on Mars, but how often, and for how long? Answering these questions will increase our understanding of Mars' habitability at a time when life was already evolving on Earth. NASA's Perseverance rover will land by the remnants of an ancient river delta in Jezero crater. Here we develop a new model to calculate the pace of shifting Martian rivers, which, when applied to orbital observations of the Jezero delta, allows us to determine a minimum duration for delta formation. Combined with an independent estimate for the total duration of delta formation (including dry spells), our results suggest that the delta took a few decades to form over a total timespan of, most likely, hundreds of thousands of years. This result suggests that Mars was likely arid at the time, with rivers flowing for at least 1 Martian day every 15-30 Martian years, and possibly more often. Nonetheless, we predict that sediments would have been buried quickly in the delta, favoring the long-term preservation of possible organic matter. Altogether, our results confirm that Jezero crater is a prime location to understand Mars' early climate, look for traces of ancient Martian life, and return samples from for further analysis on Earth.

Constraining the Timespan of Fluvial Activity From the Intermittency of Sediment Transport on Earth and Mars

“…The lower 5% bound on our data of  f I 0.0064 is significantly larger than the values of  0.0001 f I estimated for two local studies on Mars (Buhler et al, 2014;Lapôtre & Ielpi, 2020). These relatively low f I values on Mars could indicate major differences in ancient martian fluvial systems from their terrestrial counterparts-they could represent very low sediment-generation rates and/or high precipitation rates, or they could represent additional sources of intermittency beyond those present on Earth, such as a cold and icy climate with episodic clement climates induced by rare volcanic or impact events (e.g., Segura et al, 2002;Halevy & Head, 2014).…”

“…The shaded region represents common values for rivers on Earth ( = 0.01–1). Martian values are from (Buhler et al., 2014; Lapôtre & Ielpi, 2020).…”

“…Figure 3. (a) Histogram of the number of study locations versus the intermittency factor for our study of terrestrial rivers and deposits, and for deposits on Mars showing the values assumed in previous work and the values calculated for Mars(Buhler et al, 2014;Lapôtre & Ielpi, 2020). (b) Calculated depositional timespan for previously studied Mars deposits using the 5th, 50th, and 95th percentile values of intermittency factors from this study.…”

A Proposed Geobiology-Driven Nomenclature for AstrobiologicalIn SituObservations and Sample Analyses

“…The focus of the Mars program at the beginning of the Spirit and Opportunity rover missions had been to “follow the water.” The discovery of layered bedrock, the presence of spherical Fe-oxide concretions (“blueberries”), and a host of other water/rock features at Meridiani Planum showed that this site was host to several groundwater recharge events (McLennan et al , 2005 ; McLennan, 2012) and had a stagnant paleo-groundwater table for a significant amount of time (Ehlmann et al , 2011 ). Later with the Curiosity rover mission to Gale crater (Hurowitz et al , 2017 ) and the upcoming Perseverance rover mission to Jezero crater (Lapôtre and Ielpi, 2020 ), the shift to habitable environments on Mars has linked the ancient stable surface waters of the late Noachian to areas where sedimentary outcrop could reveal signs of life (Westall et al , 2015 ).…”

The Hydrogeomorphic History of Garu Crater: Implications and Constraints on the Timing of Large Late‐Stage Lakes in the Gale Crater Region

“…The instantaneous bankfull discharge estimate could balance evaporation for fluxes up to ∼170–560 m 3 /s. However, bankfull flows occur on roughly yr −1 timescales on Earth and Lapôtre and Ielpi (2020) estimate intermittency for the western delta in Jezero crater ranging between ∼10 −2 and 10 −6 day −1 , with a best fit estimation of ∼10 −4 day −1 , or ∼1 day of flow per decade. Assuming that these same timescales apply to Garu (i.e., ∼1 day of flow per year to ∼1 day of flow per decade), intermittent bankfull surface runoff would be insufficient to sustain a large lake.…”