Auros was a planet. At the time he was assigned the mission of hunting down Blake, Travis was suspended from duty and awaiting court-martial for allegedly ordering the massacre of an unspecified number of civilians there.
(See also Zircaster. This assumes that Travis was responsible, and due to be court-martialled, for two quite separate massacres. Given even his superiors regarded him as 'psychotic' this does not seem very improbable.)