I study planetary surface evolution, especially as it relates to impact events. Below, find a few abstracts from the projects I have been working on.

CONSTRAINING THE FRACTION OF ANCIENT MARTIAN VALLEYS DESTROYED BY IMPACT EVENTS.  Grace .O. Fanson 1, Gaia Stucky de Quay 1

1Massachusetts Institute of Technology (MIT); Department of Earth Atmospheric and Planetary Sciences

Introduction: In recent years, valleys and craters have shed light on Mars’ paleoclimate conditions, helping us better understand how Mars evolved as a whole [1]. Valley networks carved by liquid water [2], sprawling across almost half a million kilometers, reveal that Mars’ ancient climate supported a full water cycle up to 3.5 Gya. Additionally, this ancient wet climate allowed lakes to fill to the point of catastrophic flooding, carving deep canyons in the surface [3]. These lake breach floods are responsible for almost a quarter of the volume of incised valleys on Mars despite only representing 3% of the total valley length [3]. This large disparity flags lake breach floods as one of the key features for understanding the hydroclimatic history of Mars as they are unique indicators of intermittent periods of intense catastrophic flow unlike anything seen on Earth [4]. Understanding the role these lake breach floods played in shaping the planet’s surface is essential for understanding Mars’ evolution over time.

Because Mars does not have plate tectonic-driven resurfacing, its surface acts as a time capsule, preserving surface features like river valleys and craters for billions of years and allowing us to peer back in time at the planet’s paleoclimate. Remnants of rivers valleys, lakes, lake outflows, and impact craters seemingly work together to tell the story of Mars. However, the Martian surface is an unreliable narrator. When fluvio-lacustrine features and impactors interact, they can destroy parts of the narrative, biasing the data we collect [5]. We must consider competing erosional forces to avoid being hoodwinked.

This study aims to discover the extent to which impacting events alter the story, in particular the relative importance of large, catastrophic flood events vs. smaller, persistent surface flows that are coupled to the hydroclimate. Could impact events have preferentially destroyed small valley networks, leaving us with a disproportionate number of deep overflow canyons? Valley network morphology is a key metric for understanding paleowater availability on Mars [6,7]. Thus, valley network destruction could result in significant underestimates for how much liquid water may have existed on the ancient surface, impacting our understanding of the climatic conditions and habitability of early Mars.  

Methods: We modeled the destruction of valleys under Mars-like impacting rates to track the erosional volume changes over time for two valley populations: valley networks and lake overflow valleys (canyons).

We first identified an appropriate Earth analog site to use as our baseline, un-cratered topography for forward modelling. To ensure our study location was representative of both valley networks and overflow valleys, we used analog topography with large width (O(100 m)) valleys and narrow width (O(10 m)) river valleys that are comparable in magnitude to their Martian counterparts. One such analog location is Kohala, a peninsula on the Island of Hawai’i. We used Digital Elevation Models (DEMs) from the United States Geological Survey (USGS), with 10 m/px resolution, allowing us to resolve the smallest river valleys in our study and track changes in volume due to impactors greater than 10 m in diameter.

To create our impacting model we calculated the spatial density of craters of a given diameter at a given time in Mars’ history [8]. Then, we randomly generated crater center locations to place our bowl-shaped crater topography established by [9]. This topography consists of an excavation portion (the bowl of the crater) and a deposition portion (the ejecta blanket.) If any part of the excavation or deposition is greater in magnitude than the depth of the intersecting valley we consider that portion of the valley to be destroyed. In this way, small impacts will not have as much destructional ability as larger impacts. Then, we tracked the preservation rate of valleys varying in width over the course of 3.5 Ga. We ran this model 100 times to reduce the effect impact crater stochasticity.

Finally, our model validation includes reconstructing large valleys on Mars. Because our model predicts these valleys will be largely preserved, we can calculate the amount of destruction they were subjected to and compare the resulting preservation to that of our model. This process would be impossible for the small valleys because, if our model is correct, the small valleys would be either destroyed beyond recognition or  completely preserved. This make sense, because an impactor is less likely to hit a smaller piece of topography, but if it does, the small feature is less likely to ‘survive’. Because of this ‘survivorship bias’, measuring the preservation of the remaining valley networks would not indicate the accuracy of our model. Thus we can only measure the preservation rate of the larger valleys.

Results: The results of this project constrain the extent to which impact cratering could have altered the fluvial record of Mars. Our model shows that large valleys are indeed preferentially preserved over small valley networks. This result suggests there may have been valleys on Mars we have not accounted for, or included in our liquid water abundance calculations.

Preliminary results suggest present-day geomorphic records may be missing over half of river valley networks with depths O(10 m). In comparison, valleys of with depths O(10 m) are largely preserved (>90%). This would suggest water volume estimates used to determine global equivalent layers could be much higher, and that the majority of higher stream order tributaries are missing from the Martian surface records (from impact erasure alone). By providing quantitative constraints on potential fluvial destruction, such impacting models can provide a better understanding of the ancient water availability and habitability on Mars. 

 References:

 [1] Kite, E. S. (2019). Geologic Constraints on Early Mars Climate. Space Science Reviews, 215(1), 10. [2] Pieri, D. C. (1980). Martian Valleys: Morphology, Distribution, Age, and Origin. Science, 210(4472), 895–897. [3] Goudge, T. A., Morgan, A. M., Stucky de Quay, G., & Fassett, C. I. (2021). The importance of lake breach floods for valley incision on early Mars. Nature, 597(7878), Article 7878. [4] Stucky de Quay, G., Goudge, T. A., Kite, E. S., Fassett, C. I., & Guzewich, S. D. (2021). Limits on Runoff Episode Duration for Early Mars: Integrating Lake Hydrology and Climate Models. Geophysical Research Letters, 48(15), e2021GL093523. [5] Baum, M., Sholes, S., & Hwang, A. (2022). Impact craters and the observability of ancient martian shorelines. Icarus, 387, 115178. [6] Luo, W., Cang, X., & Howard, A. D. (2017). New Martian valley network volume estimate consistent with ancient ocean and warm and wet climate. Nature Communications, 8(1), 15766. [7] Rosenberg, E. N., Palumbo, A. M., Cassanelli, J. P., Head, J. W., & Weiss, D. K. (2019). The volume of water required to carve the martian valley networks: Improved constraints using updated methods. Icarus, 317, 379–387. [8] Michael, G. G. (2013). Planetary surface dating from crater size–frequency distribution measurements: Multiple resurfacing episodes and differential isochron fitting. Icarus, 226(1), 885–890. [9] Howard, A. D. (2007). Simulating the development of Martian highland landscapes through the interaction of impact cratering, fluvial erosion, and variable hydrologic forcing. Geomorphology, 91(3), 332–363.

Mars:

Enceladus:

Enceladus, a frigid (70K) icy satellite of Saturn, is home to unexpectedly relaxed impact craters. Low surface temperatures combined with low gravity (0.11 m/s^2) should not allow for such levels of viscous relaxation which suggests a history of heat flux from beneath the satellite’s icy shell. Previous studies have tried to build a better understanding of this heat flux by studying the depth/diameter (d/D) ratios of today’s relaxed impact craters. An updated map of the d/D ratios of impacts on Enceladus has recently been published (2024), increasing our dataset from ~150 craters to ~4,000 craters (Blanco-Rojas et al. 2024). This robust dataset measures the average d/D ratio of craters on Enceladus to be ~0.177 compared to previously measured values of ~0.11. This 61% increase has significant implications for the heat flux we expect. To determine more updated heat flux conditions, I will create a Python model to simulate the evolution of freshly impacted ice according to the Navier-Stoke’s Equation in the case of a Reynolds numbers << 1, fluid flow constitutive relations, and various heat-flux conditions. This study will result in a set of thermodynamic scenarios that could produce a crater d/D ratio of 0.177. Applying fundamentals to this problem will help me internalize concepts of continuum mechanics.