By reputation. He's an Oxford educated psychologist, who wrote a monograph on serial killers and the occult, that helped to catch Monty Props in 1988. Generally thought of as the best analyst in the violent crimes section. He had a nickname at the academy... Spooky Mulder.
More or less. The reason you're here, Agent Scully, is we want you to assist Mulder on these X-Files. You'll write field reports on your activities along with your observations on the validity of the work.
Logically I would have to say no. Given the distances need to travel from the of reaches of space the energy requirements would exceed a spacecraft's capabilities ...