A biologist friend of mine has this to say on the paper
And I quote:
"I actually read the paper. No predictive or even explanatory value,
they analyze a posteriori and don't address chirality at all. Their
arguments about the possible reasons for which amino acids are used
in biomolecules are hand-waving, frankly.
"Plotting a few charts and obvious thermodynamic analyses (glycine
forms more easily than tryptophan, who would have thunk!) sure
beats doing the painstaking stuff."
Clearly we have to get out there and just find the darn aliens!