When Galactica first picked up the distress signal, Adama was understandably suspicious. But there had been ships lost in the exodus from New Caprica, and it was possible some of them had jumped to the wrong coordinates, lost now even from the tiny life-raft of humanity. He sent a raptor, and told them to expect anything.

That *didn't* cover a human man floating unconcious and unprotected in the middle of deep vacuum, however. At their bewildered and not entirely un-panicked communication to Galactica, the man woke up and broke into their conversation, introducing himself as Alan Scott of Earth.

The panic didn't exactly *die down* at this announcement.

In the end, Alan becomes a great ally -- protecting humanity from homicidal robots is a cause he's had practice in getting behind, after all -- and he and Adama forge a friendship based on mutual respect. They spend their time fighting Cylons and trying to find earth and having quiet, manly conversations about leadership and legacy and how, exactly, you face the child left behind.

(Until the effects of the last Crisis wear out, at least, and Alan is returned back to Earth through some pseudo-physical explanation I can't be bothered to make.)