Pluto's atmosphere after New Horizons: results from stellar occultations in 2017 and 2018
Abstract
Stellar occultations have been employed for the last thirty years to characterize Pluto's atmosphere. The atmospheric pressure has increased between 1988 and 2015 (e.g. Bosh et al. 2013; Sicardy et al. 2015). Evolution in the shape of the occultation light curves over time has revealed waves in the upper atmosphere (e.g. Hubbard et al. 2009; Person et al. 2008) and suggests a thermal gradient, possibly combined with extinction-generating events, in the lower atmosphere (e.g. Elliot et al. 2007; Olkin et al. 2014). Occultation data have been combined with volatile transport models (Hansen & Paige 1996; Young 2013) to predict Pluto's atmospheric properties during and beyond the 2015 flyby of NASA's New Horizons spacecraft. Some models indicate that Pluto's atmosphere should collapse over a relatively short timescale; however, recent results are consistent with models that have no atmospheric collapse, stemming from high thermal inertia and a permanent, northern cap (e.g. Olkin et al. 2015). Here, we report results from two stellar occultations by Pluto, in 2017 and 2018. A single chord was observed at each epoch. The first occultation was on 2017 August 07, with a shadow path over the Pacific Ocean. The star had visible magnitude of 14.5, with relative velocity of 20.8 km s-1. Observations were taken from NASA's 3-m Infrared Telescope Facility in Hawaii. The dataset includes 2.5-second, visible-wavelength images from MORIS (MIT Optical Rapid Imaging System), and low-resolution, near-infrared spectra from SpeX with 3-second integration time. The second occultation was on 2018 April 09, with a shadow path over the western United States. The star had visible magnitude of 17.9, with relative velocity of 6.4 km s-1. Visible-wavelength images, at 10 Hz, were taken from the 4.3-m Discovery Channel Telescope in Arizona with a POETS (Portable Occultation Eclipse and Transit System). The 2018 observation was central, with half-light to half-light chord length of 2280 km. The 2017 observation had half-light to half-light chord length of 1650 km. The shape of both light curves is indicative of a body with an atmosphere. We present results for atmospheric model fits to these light curves and place them in context.
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #50
- Pub Date:
- October 2018
- Bibcode:
- 2018DPS....5050202S