From Guy Cox, Sydney, Australia
It was great to read that finally someone is thinking outside the box in the search for life (24 March, p 40). One simple and definitive test for life wasn't mentioned. Complex carbon compounds such as sugars and amino acids typically have two chemically identical forms, called enantiomers, that are mirror images of each other.
Non-biological processes produce both in equal amounts. In our biology, structure is important and only one version of each compound is formed – the opposite-handed version just doesn't fit. This would surely have to apply equally to any carbon-based biology. So seeing a preponderance of one enantiomer over its mirror image would be an unmistakeable indicator of life.
Also, Leah Crane refers to “dark, oily liquids” on Titan. I have used liquid ethane in my research, at temperatures found on Titan, and it is a clear liquid that looks to be much less viscous than water.
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The editor writes:
• The researchers respond that liquid methane and ethane indeed look like gasoline or petrol. But, as with water, you would see the colour of the sky in the deeper lakes and seas.
