Antonio Macias Canizares

(Advisor: Prof. Dimitri Mavris)

will defend a doctoral thesis entitled,

Volatile Molecular Species and their Role in Planetary Surface Morphology and Spacecraft Design and Performance

On

Wednesday, March 27 at 2:00 p.m. EDT

Collaborative Visualization Environment (CoVE)

Weber Space Science and Technology Building (SST III)

and

Microsoft Teams

Abstract

            The geologic processes that govern the surface morphology of ice-covered, airless (i.e., without atmospheres) bodies in the Solar System have gained increasing interest over the past several decades, both for the scientific questions such worlds present, and for the relevance for future in-situ exploration. Though engineering capabilities for landing spacecraft, such as terrain relative navigation and hazard avoidance, can mitigate against meter and sub-meter scale hazards, it is nevertheless important to understand the morphological evolution and steady state of the surface ice on these worlds. Considerable work has been dedicated to the large- and small-scale geology of these worlds, but much remains to be understood about the centimeter- to meter-scale morphology of these icy, cryogenic (~100 K) surfaces.

One specific hypothesis, is that blade-like structures, called penitentes, form on the surface of Europa, and rise up to 15 meters in height, though it has been argued that the physics of penitente formation, as applied for such a hypothesis, does not apply to the exosphere and surface conditions of Europa. Interestingly, penitente-like structures have been observed on Pluto, which does have a significant, albeit seasonal, atmosphere. Penitentes are also predicted to form under certain conditions on Mars though they have yet to be observed. On Earth, penitentes are made from compact snow or ice and achieve quasi-stability in high-altitude, low-latitude regions, as the result of sublimation and melting processes, and importantly, they only occur in regions of net sublimation (or melting) loss of water. Penitentes are erosional features that form as a series of corrugated ridges and troughs that run parallel to the path of the Sun across the sky, and mature structures often yield fields of individual spikes or blades, which bear some resemblance to a pair of hands praying toward the Sun, hence the name 'penitentes.'

The first sightings of penitentes date back to the era of Darwin, who, on a perhaps anecdotal note during his travel through Chile and La Plata, described the characteristic shape of penitentes as ``...pinnacles or columns...,'' and hypothesized their formation process: ``...the columnar structure must be owing to a `metamorphic' action, and not to a process during deposition.'' As it turns out, Darwin was correct since deposition during snowfall is the end of the life cycle for a penitente field on Earth. More importantly, Darwin described in his journal the possible hazards for travel and commerce as he experienced different scenarios during his journey. Darwin attributed the discovery of Penitentes to Scoresby and later to Colonel Jackson. Nevertheless, the true discoverers were the local inhabitants who had already named places like Cerro de los Penitentes (Hill of the Penitents) and Rio de los Penitentes long before Darwin arrived. It should be noted that during the XIX century, these snow structures might not have been locally referred to as penitentes, and even nowadays, the name penitentes is often termed after the physical process causing their formation and not their characteristic shape. Hence, places such as the Cerro de los Penitentes were most likely named after the penitents (repenting people) from the church.

To advance our understanding of the surface morphology of airless, ice-covered worlds, and to address the limitations of current models, the work in this dissertation focused on developing numerical models that accurately represent the irradiance and physical evolution of ice on such worlds and used those models to investigate the possible presence of penitentes on Europa and their hazardous implications for a future lander.

Committee

• Prof. Dimitri Mavris – School of Aerospace Engineering (advisor)
• Prof. Christopher Carr – School of Aerospace Engineering
• Prof. John Dec – School of Aerospace Engineering
• Prof. David Goldstein – School of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin
• Prof. Philip Varghese – School of Aerospace Engineering and Engineering Mechanics, The University of Texas at Austin
• Dr. Kevin Hand – NASA Jet Propulsion Laboratory