The Origin of RNA Precursors on Exoplanets

TL;DR

This study investigates the UV light requirements for prebiotic molecule formation on exoplanets, identifying which stars can support such chemistry and how it overlaps with habitable zones.

Contribution

It experimentally measures reaction rates for UV-driven prebiotic chemistry and defines 'abiogenesis zones' around different star types based on UV flux.

Findings

SO₃²⁻ light chemistry effective around stars hotter than K5

Abiogenesis zones overlap with habitable zones for certain stars

HS⁻ light chemistry too slow for prebiotic synthesis

Abstract

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.