Detection of propadiene (CH2CCH2), propene (C3H6) and non-detection of propane (C3H8) in Jupiter’s northern polar stratosphere

Journal article

We report the first detection of stratospheric propadiene (CH₂CCH₂) and propene (C₃H₆) at Jupiter’s mid-to-high northern latitudes using IRTF-TEXES measurements recorded on March 5-6, 2025. Using radiative transfer software to quantitatively test for the presence of propadiene and propene, we report a >12-σ detection of propadiene and a >17-σ detection of propene at high latitudes inside Jupiter’s auroral region, where the species are most concentrated. For example, at 62 °N (planetocentric) inside Jupiter’s northern auroral region (henceforth ‘NAR’), we derive a 1-mbar propadiene abundance of 2.0 ± 0.2 ppbv, which is 40 ± 3 higher than abundances predicted by the Moses and Poppe (2017) photochemical model (henceforth ‘MP17’), and significantly higher than the 1.2-pbbv upper limit abundance derived at 42 °N (the lowest latitude sampled by the observations). Similarly, we derive a 1-mbar propene abundance 8.1 ± 0.5 ppbv at 62 °N inside Jupiter’s NAR, which is 28 ± 2 higher than the MP17 predicted abundance and significantly higher than the 6-ppbv 1-mbar upper limit abundance derived at 42 °N. The fact that propadiene and propene are most enriched inside Jupiter’s NAR strongly suggests that perturbations to the chemistry by auroral-related heating and exogenous ions/electrons are responsible for their significant enrichment, as has been observed for other unsaturated/aromatic hydrocarbon species. Spectral features of propane (C₃H₈) were not detected at any of the locations sampled by the data (poleward of 42 °N): 3-σ upper limits of ~10 ppbv at 10 mbar were derived at 62 °N inside Jupiter’s NAR, which is ~2.5 times the MP17 predicted abundance. The non-detection of propane could, in part, be explained by the vertical sensitivity of its mid-infrared emission lines to deeper pressures, where there is negligible auroral-related heating to warm the line forming region. The results of this work strongly advocate for development of ion-neutral chemistry models of Jupiter’s polar stratosphere to quantify how strong auroral-related heating and magnetospheric particles modify the reaction pathways that produce higher-order hydrocarbons.

Authors: Sinclair, JA; Greathouse, TK; Giles, RS; Sung, K; Nixon, CA

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: Elsevier
• Journal: Icarus
• Volume: 457
• Article number: 117156
• Publication date: 2026-05-09
• Acceptance date: 2026-05-05
• DOI: 10.1016/j.icarus.2026.117156
• EISSN: 1090-2643
• ISSN: 0019-1035
• Language: English
• Keywords: auroral region; infrared spectroscopy; atmospheric composition; ion-neutral reactions