The influence of galactic cosmic rays on ion–neutral hydrocarbon chemistry in the upper atmospheres of free-floating exoplanets. Issue 2 (3rd April 2014)

• Record Type: Journal Article
• Authors: Rimmer, P. B.; Helling, Ch.; Bilger, C.; Cockell, Charles; Burchell, Mark; Martins, Zita
• Is Part Of: International journal of astrobiology. Volume 13:Issue 2(2014:Apr.)
• Page Start: 173
• Page End: 181
• Publication Date: 2014-04-03
• Subjects: Exobiology -- Periodicals; 576.83905
• DOI: 10.1017/S1473550413000487
• Languages: English
• ISSNs: 1473-5504

Abstract

<abstract abstract-type="normal"> <title>Abstract</title> <p>Cosmic rays may be linked to the formation of volatiles necessary for prebiotic chemistry. We explore the effect of cosmic rays in a hydrogen-dominated atmosphere, as a proof-of-concept that ion–neutral chemistry may be important for modelling hydrogen-dominated atmospheres. In order to accomplish this, we utilize Monte Carlo cosmic ray transport models with particle energies of 10⁶ eV&lt;<italic>E</italic>&lt;10¹² eV in order to investigate the cosmic-ray enhancement of free electrons in substellar atmospheres. Ion–neutral chemistry is then applied to a <sc>Drift–Phoenix</sc> model of a free-floating giant gas planet. Our results suggest that the activation of ion–neutral chemistry in the upper atmosphere significantly enhances formation rates for various species, and we find that C₂H₂, C₂H₄, NH₃, C₆H₆ and possibly C₁₀H are enhanced in the upper atmospheres because of cosmic rays. Our results suggest a potential connection between cosmic-ray chemistry and the hazes observed in the upper atmospheres of various extrasolar planets. Chemi-ionization reactions are briefly discussed, as they may enhance the degree of ionization in the cloud layer.</p> </abstract>