Bromery Fall 2018 Seminar Series: Darrell Strobel

Description

Darrell Strobel, a professor of Earth and Planetary Sciences at Johns Hopkins University, will be giving a talk entitled "The Atmosphere of Pluto Observed by the New Horizons as Seen by a Theorist" as part of the Randolph Bromery Fall 2018 Seminar Series.

Abstract:

On 14 July 2015, NASA's New Horizons spacecraft observed an ultraviolet solar occultation of Pluto's atmosphere with its Alice ultraviolet spectrograph (Young et al. Icarus, 300, 2017) and performed a radio occultation that probed Pluto's atmosphere down to the surface (Hinson et al., Icarus, 290, 2017). The previously published results of most interest in this talk are 1) peak temperature of ~ 106 K at ~ 25 km, 2) cold isothermal temperature ~ 65-68 K in Pluto's upper atmosphere, 3) inferred CH4 surface mixing ratio ~ 0.3±0.02%, and 4) inferred enhanced Jeans escape rates are 3-7 x 1022 N2 s-1 and 4-8 x 1025 CH4 s-1 at the exobase (r ~ 2900 km, where the Kn = 0.7). I address the questions: 1) is the atmosphere spherically symmetric, 2) thickness of the planetary boundary layer, and 3) time constants governing the chemistry, diffusion, and escape of N2 and CH4. Given the length of these time constants, how do you interpret NH flyby data taken in a time interval much shorter than these time constants, some of which exceed the duration of the flight time to Pluto. Escaping CH4 takes approximately 1 Earth year to reach the edge of Pluto's Hill sphere. In spite of this I calculate the slowing down of the solar wind detected by the NH's SWAP instrument. Time permitting, I will discuss my theory on the layering of Pluto's haze.