Stability of uracil in different sulphates under Martian-like UV irradiation

Mars is one of the most probable and accessible places where life could have evolved beyond Earth. Searching for biosignatures, such as organic molecules directly or indirectly related to life, has become one of the main goals of the exploration programs on Mars. However, the occurrence of organic molecules on Mars nowadays is scarce. Among the different degradation factors of the current Martian environment, ultraviolet (UV) radiation is especially harmful as it can promote the degradation of organic molecules in a few hours. In this context, minerals may play a significant role by photoprotecting or photocatalizing the degradation of organic molecules. In this work, the effect of different sulphates (Na2SO4, MgSO4⋅6H2O, CaSO4⋅xH2O and FeSO4⋅xH2O) on the preservation of the nucleobase, uracil, against Martian-like UV radiation was studied. The UV radiation studies showed that all the sulphates present a photocatalytic effect when uracil was adsorbed in comparison to the degradation of pure uracil. Among the different sulphates, Na2SO4 and MgSO4⋅6H2O are the least photocatalytic ones while FeSO4⋅xH2O and CaSO4⋅xH2O are the most photocatalytic. The biggest photoprotection effect is likely coming from the possibility of the formation of uracil dimers, which are more stable under UV radiation than the monomer. Despite this, the calculated weighted mean half-lifetimes for uracil in all the adsorbed sulphates are long enough (t1/2 > 30 h) to allow detection by rover payload instruments before the molecule is completely degraded.