Intracrystalline lipids within sulfates from the Haughton Impact Structure—Implications for survival of lipids on Mars

Lipids can be present within gypsum as intracrystalline inclusions if they become incorporated within the mineral as is it precipitates. The lipids that comprise these inclusions are protected against alteration or destruction by an external oxidising chemical environment because a protective mineral matrix surrounds them. Sulfate minerals are abundant on the surface of Mars and were present in the samples that were analysed by the Viking landers. The quantities of secondary intracrystalline fossil-lipids that are present in samples of gypsum and gypsum-rich soils from the Haughton Impact Structure, Devon Island, Canadian High Arctic are sufficient to suggest that if a similar concentration of fossil lipids was present in the sulfate-rich samples analysed by the Viking Landers then they could have been detected. Possible reasons why a secondary fossil-lipid signature was not detected include a poor rate of conversion during pyrolysis, exposure of intracrystalline lipids during periods of weathering to oxidative martian diagenesis, a low level of biological productivity or an absence of a source for lipids on the surface of Mars. Polycyclic aromatic hydrocarbons of meteoritic origin, and terpane biomarkers such as hopanes and steranes, are not present in the Haughton gypsum in sufficient quantities to have been readily detected.