From Kevin Healey, Sydney, Australia
Using mass spectrometers in space missions to seek molecules with a high “assembly index” – an idea that springs from the new Assembly Theory of life that you reported on – is an interesting development in the search for extraterrestrial life (24 June, p 32).
Threshold values derived from life on Earth should be used with caution, however. Also, while detections exceeding the threshold could be considered a necessary condition for life, they wouldn’t, by themselves, be proof that it exists in that place.
