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Volatile Ice Precipitation and Erosion in Pluto’s Eastern Hemisphere

Presentation #105.01 in the session “Pluto System: Geology”.

Published onOct 26, 2020
Volatile Ice Precipitation and Erosion in Pluto’s Eastern Hemisphere

We are creating a global US Geological Survey Scientific Investigations Map at 1:7M scale for the >75% of Pluto’s surface that was imaged by the New Horizons spacecraft. This abstract presents mapping of the eastern hemisphere, extending from the eastern edge of the nitrogen ice plains of Sputnik Planitia (SP) to the eastern portion of the poorly resolved “far side”, covering ~180° of longitude. The bladed terrain deposits (BTDs), constructed of methane ice, dominate the equatorial region, alternating with a chain of dark maculae and eventually expiring eastwards of 74°E. A unit extending north from the near side BTDs of Tartarus Dorsa (TD) displays a characteristic arcuate morphology and is interpreted as a precursor unit underlying the BTDs. East Tombaugh Regio (ETR), situated between SP and the bladed terrain of TD, is experiencing precipitation of nitrogen ice and has previously been characterized as “pitted uplands”, but our mapping shows that this is only applicable to its southern portion, which grades into the BTDs. Its northern, hillier, portion grades into the arcuate terrain, and we therefore interpret ETR to represent an extension of the arcuate/BTD relationship all the way to the eastern edge of SP.

The northern portion of the eastern near side mapping area displays smooth uplands that have been interpreted as being covered by a thick, methane-rich mantle. The smooth uplands are best expressed in Pioneer Terra (PT), but have been eroded across much of their area (Hayabusa Terra), resulting in a rougher texture at decameter to km scale. These uplands underlie and are older than the BTDs/arcuate terrain, and appear to be exposed in a few places within ETR. Our mapping reveals that the mantled terrain extends far to the east (~330° E), where it dissipates and alternates with a darker substrate that has been exposed where the mantle has been eroded away completely, forming a mottled pattern that is detectable in far side imaging. This texture may record a history of alternating deposition and erosion of the mantle. The substrate appears to be visible on the floors of pits and craters extending as far east as Venera Terra. It has been proposed that the mantle originated via outgassing from giant pits located within western PT, but its expansive coverage, its occurrence east of SP, and its eventual fragmentation on Pluto’s far side (all of which mirror the distribution of the BTDs, but at higher latitude) perhaps indicate an origin related to the retrorotation of Pluto’s atmosphere pushing gaseous methane westwards (as identified by global climate modeling), rather than a localized geological source.

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