Code SS Weekly Highlights May 9, 2017 SMD Space Science

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Code SS Weekly Highlights May 9, 2017 SMD Space Science & Astrobiology • Geological Mapping of Sputnik Planitia on Pluto • POC: Oliver White (SST) • Short story: On May 1st 2017, Icarus journal published a special issue focusing on science results of the New Horizons flyby of the Pluto system in July 2015. Several Ames-based researchers have published first-author studies within this issue. One such study is the geological mapping of Sputnik Planitia, the giant nitrogen ice “sea” on Pluto, authored by Dr. Oliver White. Sputnik Planitia (note all feature names used are informal) forms the western half of the bright heart-shaped feature called Tombaugh Regio, and has attracted great scientific interest as a regional-scale, geologically active feature located on a planetary body that was expected to be geologically inert prior to encounter. The map documents the geology and stratigraphy of terrains that are presently being affected to some degree by the action of flowing nitrogen ice. The nitrogen ice plains of Sputnik Planitia display no impact craters, and are undergoing constant resurfacing via convection, glacial flow, and sublimation. Condensation of atmospheric nitrogen onto the surface to form a bright mantle has occurred across broad swathes of Sputnik Planitia, and appears to be partly controlled by Pluto’s obliquity cycles. The action of nitrogen ice has been instrumental in affecting uplands terrain surrounding Sputnik Planitia, and has played a key role in the disruption of Sputnik Planitia’s western margin to form chains of blocky mountain ranges, as well in the extensive erosion by glacial flow of the uplands of east Tombaugh Regio. For its size, the area of Pluto incorporating Sputnik Planitia and its immediate surroundings is perhaps unique within the outer Solar System for displaying such a wide array of geological units that present a great range of surface ages. The source of the ongoing geological activity here derives from Pluto’s special location in the Solar System, where conditions are such that exotic materials such as nitrogen and methane can exist in abundance as solids on the surface, but are still volatile enough such that they can be readily mobilized by both exogenic (climatic cycling) and endogenic (internal radiogenic heating) energy sources. The accompanying figure presents the map and a description of map units. .

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Motivation Sputnik Planitia Flexural Modeling Plans for GEOL
Motivation Sputnik Planitia Flexural modeling Sputnik Planitia Flexure model • Large teardrop-shaped basin The flexure of an elastic plate in two dimensions obeys Equation 1 located on Pluto at 20°N 180°E 푑4푤 퐷 + 푚 − 푐 푔푤 = 푉0 Equation 1. • Size: 1300 km by 900 km 푑푥4 4퐷 1/4 퐸∗ℎ3 • Depth: 3-4 km (basin) where 훼 = is the flexural parameter, 퐷 = is the flexural rigidity, is the 휌 −휌 12(1−푣2) 푚 • 푚 푐 Deposit of nitrogen ice density of the underlying layer of the ice shell, is the density of the ice shell. g is the gravity on • 푐 Water ice basement Pluto, E is the Young’s modulus of water ice, h is the elastic thickness, and 휈 is Poisson’s ratio 푑3푤 1 푑푤 For a single vertical load at 푥 = 0 , the boundary conditions are 퐷 = 푉 and = 0 Formation Hypotheses 푑푥3 2 0 푑푥 • An ancient impact basin created The deflection due to several line loads is found by superposition: 푉 훼3 푥−푥 푥−푥 푥−푥 by an impactor later filled with 푤 = σ 푖 sin 푖 + cos 푖 exp − 푖 Equation 2. 푖 8퐷 훼 훼 훼 N2 ice. The feature would have moved to the current location Where {푉푖} is the magnitude of the loads at position {푥푖} through polar wander. • Runaway deposition of N2 ice Inversion due to albedo feedback at the The load vector 퐕 that produces topography 퐰, is found by least squares optimization: ±30°. The depression is due to 퐕 = 퐌′퐌 + 퐂 −1 퐌′퐰 elastic flexure under the load of 풎 where M is the operator matrix that links a load at position 푥푗 to deflection at a point 푥푖 a thick N2 ice cap.
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Singer Et Al., 2019
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