The Origin of RNA Precursors on Exoplanets


Reaction Scheme. The scheme of light and dark reactions we explore, considering two steps along the path to forming pyrimidines (RNA precursors), one with bisulfite (SO2−) as the electron donor, and the other with hydrogen sulfide (H2S, HS−) as the electron donor.

Given that the macromolecular building blocks of life were likely produced photochemically in the presence of ultraviolet (UV) light, we identify some general constraints on which stars produce sufficient UV for this photochemistry.

We estimate how much light is needed for the UV photochemistry by experimentally measuring the rate constant for the UV chemistry (`light chemistry', needed for prebiotic synthesis) versus the rate constants for the bimolecular reactions that happen in the absence of the UV light (`dark chemistry'). We make these measurements for representative photochemical reactions involving SO$_3^{2-}$ and HS$^-$. By balancing the rates for the light and dark chemistry, we delineate the "abiogenesis zones" around stars of different stellar types based on whether their UV fluxes are sufficient for building up this macromolecular prebiotic inventory.

We find that the SO$_3^{2-}$ 'light chemistry' is rapid enough to build up the prebiotic inventory for stars hotter than K5 (4400 K). We show how the abiogenesis zone overlaps with the liquid water habitable zone. Stars cooler than K5 may also drive the formation of these building blocks if they are very active. The HS$^-$ 'light chemistry' is too slow to work even for the Early Earth.

Paul Brandon Rimmer, Jianfeng Xu, Samantha Thompson, Ed Gillen, John Sutherland, Didier Queloz
(Submitted on 8 Aug 2018)

Comments: 33 pages, 5 figures, preprint
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR); Biological Physics (physics.bio-ph)
Journal reference: Science Advances 01 Aug 2018: Vol. 4, no. 8, eaar3302
DOI: 10.1126/sciadv.aar3302
Cite as: arXiv:1808.02718 [astro-ph.EP] (or arXiv:1808.02718v1 [astro-ph.EP] for this version)
Submission history
From: Paul B. Rimmer
[v1] Wed, 8 Aug 2018 10:50:30 GMT (5988kb,D)
https://arxiv.org/abs/1808.02718
Astrobiology
Astrochemistry

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