Reconciling results of 2019 and 2020 stellar occultations on Pluto’s atmosphere

New constraints from both the 5 September 2019 event and consistency analysis

¹ Purple Mountain Observatory, Chinese Academy of Sciences, No. 10 Yuanhua Road, Nanjing 210033, PR China
e-mail: yuanye@pmo.ac.cn
² School of Astronomy and Space Science, University of Science and Technology of China, No. 96 Jinzhai Road, Hefei, Anhui 230026, PR China
³ Hunan Astronomical Association, Changsha, Hunan 410000, PR China
⁴ Department of Space Sciences and Astronomy, Hebei Normal University, No. 20 Road East. 2nd Ring South, Shijiazhuang, Hebei 050024, PR China
⁵ Shenzhen Astronomical Observatory, Tianwen Road, Shenzhen, Guangdong 518040, PR China
⁶ Shenzhen Astronomical Society, 22c Seascape Square Taizi Road, Shenzhen, Guangdong 518040, PR China
⁷ Shanghai Astronomical Observatory, Chinese Academy of Sciences, No. 80 Nandan Road, Shanghai 200030, PR China
⁸ Nanjing Amateur Astronomers Association, Nanjing 210000, PR China

Received: 16 July 2023
Accepted: 25 September 2023

Abstract

A stellar occultation by Pluto on 5 September 2019 yielded positive detections at two separate stations. Using an approach consistent with comparable studies, we derived a surface pressure of 11.478 ± 0.55 µbar for Pluto’s atmosphere from the observations of this event. In addition, to avoid potential method inconsistencies when comparing with historical pressure measurements, we reanalyzed the data for the 15 August 2018 and 17 July 2019 events. All the new measurements provide a bridge between the two different perspectives on the pressure variation since 2015: a rapid pressure drop from previous studies of the 15 August 2018 and 17 July 2019 events and a plateau phase from that of the 6 June 2020 event. The pressure measurement from the 5 September 2019 event aligns with those from 2016, 2018, and 2020, supporting the latter perspective. While the measurements from the 4 June 2011 and 17 July 2019 events suggest probable V-shaped pressure variations that are unaccounted for by the volatile transport model (VTM), the VTM remains applicable on average. Furthermore, the validity of the V-shaped variations is debatable given the stellar faintness of the 4 June 2011 event and the grazing single-chord geometry of the 17 July 2019 event. To reveal and understand all of the significant pressure variations of Pluto’s atmosphere, it is essential to provide constraints on both the short-term and long-term evolution of the interacting atmosphere and surface by continuous pressure monitoring through occultation observations whenever possible, and to complement these with frequent spectroscopy and photometry of the surface.