Transient energetic particles as the origin of the mid-infrared north polar hotspot of Jupiter
Since it was detected in 1980, Jupiter's 8-μm CH₄ north polar hot spot (8CNPHS), ∼20 K warmer than the surrounding polar stratosphere, has been observed for four decades. Unlike normal auroral ovals (i.e., the bright rings of auroral emissions), it is usually filled with bright emission. The causes of both its shape and longevity are not understood, although several mechanisms have been proposed to explain its existence. In order to investigate the deriving mechanism of the 8CNPHS, we have observed the north polar regions near 3 μm, where line emission from another CH₄ band as well as a C₂H₆ fundamental band occur. Using Gemini North/GNIRS in 2013, 2020, 2021, and 2022, we have detected transient 3-μm CH₄ and/or C₂H₆ bright spots within the 8CNPHS, and occasionally no apparent bright spots. By comparing the emission from CH₄ with that from C₂H₆, we demonstrate that the origin of the 8CNPHS must be due to transient and energetic magnetospheric particles, which can penetrate down to the hydrocarbon layers, heating the homopause (∼1 μbar level) and the stratosphere (∼1 mbar level) and energize the 8CNPHS. Based on our observations and analysis, we propose the following three mechanisms for maintaining and containing the decades long warmth of the 8CNPHS: 1) energetic and transient auroral particle precipitations warming the stratosphere of the 8CNPHS, 2) a longer radiative cooling time in the 8CNPHS stratosphere (∼6 months) compared to less than or equal to one month at the homopause, and 3) recently detected polar stratospheric jets likely associated with polar fronts, which resist the free flow of warm gas in the 8CNPHS to the surrounding polar regions. We show that other heating mechanisms proposed so far in the literature, such as Joule heating, polar haze heated by sunlight, etc., are only the secondary mechanisms that follow atmospheric ionization caused by energetic particle bombardment. Our finding of the magnetospheric-ionospheric-stratospheric coupling in the Jovian polar regions open the possibility of quantitatively refining 3-D global circulation models for the atmospheres of giant planets and exoplanets.
© 2023 Elsevier. We are grateful to the two referees for their helpful reviews. This paper is based on observations obtained for programs GN-2012B-Q-115, GN-2020A-Q-315, GN-2021A-Q-118, and GN-2022A-Q-311 at the Gemini Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc., under a cooperative agreement with the NSF on behalf of the Gemini partnership: the National Science Foundation (United States), National Research Council (Canada), CONICYT (Chile), Ministerio de Ciencia, Tecnología e Innovación Productiva (Argentina), Ministério da Ciência, Tecnologia e Inovação (Brazil), and KASI (Republic of Korea). This research was supported by K-GMT Science Program of KASI. Correspondence and requests for additional materials should be addressed to SJK (firstname.lastname@example.org). Mr. J.K. Park helped in making Fig. 1. This work was supported by the NRF grant (2022R1A2C1003604) funded by the Korean government (MSIT). Data availability. Original observational data used in this study are publicly available on https://archive.gemini.edu The authors declare no conflict of interest
Supplemental Material - 1-s2.0-S001910352300115X-mmc1.docx