Episode 84 of The Trigan Empire
aka The Search for Sibelius
De maan Gallas (Dutch title)
The Moon Gallas (Dutch title, translated)
Written by Ken Roscoe
Illustrated by Gerry Wood
Search Mission was originally published in 15 instalments in issues 1013 (8 August 1981) to 1027 (14 November 1981) of Look and Learn magazine.
To date it has not been reprinted in English.
Plot summary (Dutch)