Recent Research - Pluto Related Projects
The work presented on this page was sponsored by NASA's New Frontiers Data Analysis Program (NFDAP).
Pluto Topic 1: Loading of the Sputnik Planitia basin by nitrogen ice, with implications for regional tectonics and enhanced cryomagmatic potential.
The New Horizons Mission to Pluto revolutionized our understanding of this heretofore mysterious dwarf planet. High resolution imaging data was obtained for about half of the planet, revealing an icy landscape dominated by the bright terrain of Sputnik Planitia (the "heart" of Pluto), comprising nitrogen (N2) ice deposits filling an ancient, irregularly shaped impact basin. The elevated terrains surrounding Sputnik Planitia are disrupted by multiple sets of faults, fractures, and troughs, many of which have more or less radial orientations to central Sputnik Planitia. Figure 1 shows a topographic map of Pluto derived from stereo imaging techniques, with Sputnik Planitia centered (note: in the topographic map low elevations are dark, and therefore so is the basin) and the various tectonic systems arrayed around it.
Figure 1: Global tectonic map centered on Sputnik Planitia.
Pluto's outer shell is composed of water (H2O) ice, with scatterings of other chemicals on the surface and a massive deposit of nitrogen (N2) ice at filling the Sputnik Planitia basin. In order to evaluate the conditions that led to the observed distribution of N2 ice in the basin and tectonic features around it, we created Finite Element Method (FEM) numerical models of loading of Pluto's water ice outer shell (Pluto's "lithosphere") by the N2 ice filling the basin. A typical result for such models is shown in Figure 2 (in which the curvature of the shell is "straightened out" for ease of display). We calculate the stress components from loading in 3 directions (Figure 1A), and from these results we can predict the fault type and orientations (colors in Figure 1B, with black contours encapsulating the regions where stresses are actually high enough to break the ice). We also calculate the effects of stresses on the ability of Pluto's internal magma, which is simply the liquid water in its interior ocean, to ascend through the solid shell (Figure 1C). This sort of volcanism on icy worlds is called "cryovolcanism" or "cryomagmatism".
Figure 2: An example of an FEM model calculation for stress, faulting, and cryomagmatic enhancement. (Figure 6 of McGovern et al., 2021)
We found that the thickness of Pluto's ice shell must be between 40 and 75 kilometers in order to explain the observed distribution of faults and fractures. Figure 3 shows the results of three models, with the central model showing the best distribution of expected fault type (the thick yellow band in Figure 3b, indicating radial normal faulting) at intermediate shell thickness, whereas shells that were thinner (Figure 3a) or thicker (Figure 3c) displayed fault types that strongly differ from observations (white and orange bands in those Figures, indicating mixed mode and concentric normal faults, respectively). We also determined that the initial basin needed to be shallow, less than about 3 km deep: otherwise, it would be impossible to fill up the basin with N2 ice to the observed level without shattering the lithospheric shell.
Figure 3: An example of three FEM models showing effect of shell thickness on fault style. (Figure 10 of McGovern et al., 2021)
Reference: McGovern, P. J., O. L. White and P. M. Schenk, Tectonism and Enhanced Cryovolcanic Potential Around a Loaded Sputnik Planitia Basin, Pluto, J. Geophys. Res., 126, e2021JE006964. https://doi.org/10.1029/2021JE006964, 2021.
Supplementary Reference: Stern, S. A., O. L. White, P. J. McGovern, J. T. Keane, J. W. Conrad, C. J. Bierson, C. B. Olkin, P. Schenk, J. M. Moore and K. Runyon, Pluto’s Far Side, Icarus, doi:10.1016/j.icarus.2020.113805, 2020.
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