On the stability of molecules and microorganisms in interstellar and planetary environments

Abstract

Many organic molecules have been detected in interstellar environments and even more are found in the solar system, for example in comets and meteorites. Some of these molecules are also found in living organisms on Earth, suggesting that there might be a connection between star dust and the origin of life on Earth. Before life could emerge on Earth, the building blocks for life had to be present. It is likely that both indigenous and external sources have contributed to the organic inventory on the early Earth. In this thesis, the photostability of several organic compounds was analysed in simulated interstellar environments. The results show that nucleobases and their precursors are rapidly destroyed in most interstellar environments and in the solar system, if they reside in the gas phase. Mars is annually supplied with 2.4_10(5) kg of carbon by meteoritic impact. Despite this supply, the Viking landers did not detect any organic molecules in the martian surface above a detection limit of a few ppb. The discrepancy is usually attributed to oxidizing reactions in the martian soil. In this thesis the stability of amino acids in Mars soil analogues is investigated. The results show that the stability is dependent on soil mineralogy. While destruction of amino acids in Atacama desert soil and Orgueil meteorite samples is rapid, deposits from the Danish Salten Skov region show negligible loss of amino acids after exposure to a simulated Mars environment. We conclude that clay-type minerals can protect organic molecules against destruction. Our results provide support for future life detection missions to Mars and a proper landing site selection. We have tested the survival of halophilic archaeon Natronorubrum sp. strain HG-1 under conditions similar to those found on Mars. The results show that Natronorubrum strain HG-1 can be desiccated and rehydrated with a negligible effect on its growth, but that these organisms did not survive exposure to martian UV. Natronorubrum cells were also incapacitated by high temperature (70 _C), while low temperature (__20 _C) severely affected the growth. Cells did not survive desiccation in combination with Atacama desert soil. From these results we conclude that Natronorubrum strain HG-1 is not likely to survive in a martian environment.