On Tue, 30 Apr 1996, The Major wrote:

cave and accidentally freed... and I really can't work out what brought 
Aeka & Sasami to earth.  Kiyone turns up around episode #4 (I think) and 

Well, Aeka showed up because she received a distress call.  (Mihoshi's, 
after her ship and Ryo-oh-ki crashed)  Sasami showed up because she 
wondered where her big sister went. :)