  Let $F$ be a perfect field and $M^*(F)$ the nonassociative simple Moufang
loop consisting of the units in the (unique) split octonion algebra $O(F)$
modulo the center. Then $Aut(M^*(F))$ is equal to $G_2(F) \rtimes Aut(F)$. In
particular, every automorphism of $M^*(F)$ is induced by a semilinear
automorphism of $O(F)$. The proof combines results and methods from geometrical
loop theory, groups of Lie type and composition algebras; its gist being an
identification of the automorphism group of a Moufang loop with a subgroup of
the automorphism group of the associated group with triality.
