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Ancient Climate and Volatile Loss during Pluto’s Wild Years, 4.5 Gy ago

Presentation #303.01 in the session Pluto through the Ages.

Published onOct 20, 2022
Ancient Climate and Volatile Loss during Pluto’s Wild Years, 4.5 Gy ago

Pluto did not form at its present-day location, but rather formed closer to the Sun, likely around 30 AU, before migrating to its current semi-major axis of 40 AU. During this migration, Pluto was tossed around the solar system due to the migration of Neptune and the other giant planets. This great migration, which we term “the Wild Years,” likely lasted for ~100 My and began 4.5 Gy ago. At that time, the Sun was not yet on the main sequence and its output was very different than today; the EUV flux could have been as much as 100 times higher, while the bolometric luminosity was just 70% of the present-day value. Pluto was probably differentiated with N2 on the surface, but had a higher internal heat flux. Dynamical models show that Pluto and its fellow plutinos (Kuiper Belt objects currently in 3:2 resonance with Neptune) could have orbited as close as 10 AU and as far as 100 AU from the Sun. In this talk, we will discuss what these effects (different solar luminosity, internal heat, and heliocentric distances) have on the atmospheric escape rate and N2 inventory for early Pluto. We model the early sun behavior, the internal heat budget, and the orbital migration for a suite of ~50 hypothetical plutinos and determine the resulting climate, namely surface pressure, surface temperature, and upper atmosphere temperature. From this, we are able calculate to the rate of atmospheric escape over the 100 My “Wild Years” period. We also estimate the impact history during this time period to calculate both the delivery and the loss of volatiles from impacts, as well as the photochemical destruction rate of N2. Together, this allows us to estimate the primordial N2 inventory of Pluto and compare to the present-day inventory. Understanding the primordial inventory allows constraints to be placed on the scale of purported ancient glaciation and sublimation landforms.

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