Planetary science is often limited to only surface observations of planets requiring the
development of modeling techniques to infer information about the planet’s interior. This work
outlines three separate scientific problems that arose from planetary surface observations, the
methodology utilized to explain the formation of these observation, and what we learned about the
planet’s interior by solving these problems.
Chapter 1 discusses why lunar mascon basins (impact basins associated with a central freeair gravity positive) form for only a limited range of basin diameters. Modeling the full formation
of South-Pole Aitken (SPA) basin using a sequential two-code (hydrocode and Finite Element
Model) shows that due to SPA’s great size (long wavelength) and the high geothermal gradient of
the Moon at impact, the basin’s relaxation process was controlled by isostatic adjustment with
minimal influence from lithospheric rigidity or membrane stresses. Additionally, the modeling
shows that the Moon was hot and weak at impact.
Chapter 2 addresses why there is a lack of olivine abundance on Mars around large impact
basins, and the formation of the megabreccia that is associated with an orthopyroxene signature in
the circum-Isidis Planitia region. Hydrocode modeling of the excavation of the Isidis forming
impact shows the impact was more than capable of excavating mantle material and reproducing
the observed megabreccia. This coupled with the lack of olivine signature indicates that the
Martian upper mantle is orthopyroxene-rich.
Chapter 3 covers the investigation into why the nitrogen ice sheet on Pluto, Sputnik Planitia,
is the youngest observed terrain and why the surface is divided into irregular polygons about 20–
30 kilometers in diameter. The utilization of a new parameterized convection model enables the
computation of the Rayleigh number of the nitrogen ice and shows that the nitrogen ice is
vigorously convecting, making Rayleigh–Bénard convection the most likely explanation for these
polygons (Trowbridge et al., 2016). Additionally, the diameter of Sputnik Planitia’s polygons and
the dimensions of its ‘floating mountains’ of water ice suggest that its nitrogen ice is about five to
ten kilometers thick (Trowbridge et al., 2016). The estimated convection velocity of 1.5
centimeters a year indicates a surface age of only around a million years (Trowbridge et al., 2016).
The accumulation of this work is three chapters that use three separate techniques to further
understand three separate planets.
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/12685868 |
| Date | 29 July 2020 |
| Creators | Alexander J Trowbridge (9149009) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/From_the_Moon_to_Pluto_the_Use_of_Impact_and_Convection_Modeling_as_a_Window_Into_Planetary_Interiors/12685868 |
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