000601421 001__ 601421 000601421 005__ 20250715173234.0 000601421 0247_ $$2doi$$a10.1093/mnras/stad900 000601421 0247_ $$2ISSN$$a0035-8711 000601421 0247_ $$2ISSN$$a1365-2966 000601421 0247_ $$2ISSN$$a1365-8711 000601421 0247_ $$2arXiv$$aarXiv:2303.07058 000601421 0247_ $$2altmetric$$aaltmetric:143808507 000601421 0247_ $$2WOS$$aWOS:001023517100072 000601421 0247_ $$2openalex$$aopenalex:W4360942250 000601421 037__ $$aPUBDB-2024-00175 000601421 041__ $$aEnglish 000601421 082__ $$a520 000601421 088__ $$2arXiv$$aarXiv:2303.07058 000601421 1001_ $$0P:(DE-H253)PIP1091703$$aRodgers-Lee, D.$$b0$$eCorresponding author 000601421 245__ $$aThe energetic particle environment of a GJ 436 b-like planet 000601421 260__ $$aOxford$$bOxford Univ. Press$$c2023 000601421 3367_ $$2DRIVER$$aarticle 000601421 3367_ $$2DataCite$$aOutput Types/Journal article 000601421 3367_ $$0PUB:(DE-HGF)16$$2PUB:(DE-HGF)$$aJournal Article$$bjournal$$mjournal$$s1709281909_741177 000601421 3367_ $$2BibTeX$$aARTICLE 000601421 3367_ $$2ORCID$$aJOURNAL_ARTICLE 000601421 3367_ $$00$$2EndNote$$aJournal Article 000601421 500__ $$a14 pages, 9 figures, accepted for publication in MNRAS Waiting for fulltext 000601421 520__ $$aA key first step to constrain the impact of energetic particles in exoplanet atmospheres is to detect the chemical signature of ionization due to stellar energetic particles and Galactic cosmic rays. We focus on GJ 436, a well-studied M dwarf with a warm Neptune-like exoplanet. We demonstrate how the maximum stellar energetic particle momentum can be estimated from the stellar X-ray luminosity. We model energetic particle transport through the atmosphere of a hypothetical exoplanet at orbital distances between a = 0.01 and 0.2 au from GJ 436, including GJ 436 b’s orbital distance (0.028 au). For these distances, we find that, at the top of atmosphere, stellar energetic particles ionize molecular hydrogen at a rate of ζStEP,H2 ∼ 4 × 10−10 to 2 × 10−13 s−1. In comparison, Galactic cosmic rays alone lead to ζGCR,H2 ∼ 2 × 10−20–10−18 s−1. At 10 au, we find that ionization due to Galactic cosmic rays equals that of stellar energetic particles: ζGCR,H2 = ζStEP,H2 ∼ 7 × 10−18 s−1 for the top-of-atmosphere ionization rate. At GJ 436 b’s orbital distance, the maximum ion-pair production rate due to stellar energetic particles occurs at pressure P ∼ 10−3 bar, while Galactic cosmic rays dominate for P > 102 bar. These high pressures are similar to what is expected for a post-impact early Earth atmosphere. The results presented here will be used to quantify the chemical signatures of energetic particles in warm Neptune-like atmospheres. 000601421 536__ $$0G:(DE-HGF)POF4-613$$a613 - Matter and Radiation from the Universe (POF4-613)$$cPOF4-613$$fPOF IV$$x0 000601421 588__ $$aDataset connected to CrossRef, Journals: bib-pubdb1.desy.de 000601421 693__ $$0EXP:(DE-MLZ)NOSPEC-20140101$$5EXP:(DE-MLZ)NOSPEC-20140101$$eNo specific instrument$$x0 000601421 7001_ $$00000-0002-7180-081X$$aRimmer, P. B.$$b1 000601421 7001_ $$00000-0001-5371-2675$$aVidotto, A. A.$$b2 000601421 7001_ $$00000-0002-3191-2200$$aLouca, A. J.$$b3 000601421 7001_ $$0P:(DE-H253)PIP1080492$$aTaylor, A. M.$$b4 000601421 7001_ $$00000-0002-2378-7040$$aMesquita, A. L.$$b5 000601421 7001_ $$aMiguel, Y.$$b6 000601421 7001_ $$00000-0003-2854-765X$$aVenot, O.$$b7 000601421 7001_ $$aHelling, C.$$b8 000601421 7001_ $$aBarth, P.$$b9 000601421 7001_ $$aLacy, E.$$b10 000601421 773__ $$0PERI:(DE-600)2016084-7$$a10.1093/mnras/stad900$$gVol. 521, no. 4, p. 5880 - 5891$$n4$$p5880 - 5891$$tMonthly notices of the Royal Astronomical Society$$v521$$x0035-8711$$y2023 000601421 7870_ $$0PUBDB-2024-00490$$aRodgers-Lee, D. et.al.$$dOxford : Oxford Univ. 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