A critical nutrient used to produce the neurotransmitter serotonin may have turned up in samples collected from asteroid Bennu by NASA's OSIRIS-REx mission. Tryptophan is one of the nine essential amino acids that the human body cannot make on its own, and, if confirmed, its detection in Bennu by researchers from NASA and the University of Arizona would mark the first time it has ever been found in an extraterrestrial sample. It's a discovery that bolsters the theory that rocks from space