Episode 85 of The Trigan Empire
Alien Mission
aka De maan Gallas II (Dutch title)
The Moon Gallas II (Dutch title, translated)
Written by Ken Roscoe
Illustrated by Gerry Wood
Alien Mission was originally published in 12 instalments in issues 1028 (21 November 1981) to 1039 (6 February 1982) of Look and Learn magazine.
To date it has not been reprinted in English.

Plot summary
After the eruption of the volcano on Gallas, a metal monster drives out of an underground cave. When Volpus returns to Gallas to look for diamonds, he is seized by a tentacle of the steel monster. He is examined inside the machine and, without realizing anything, is set back on Gallas not much later. When his men see the metal monster, they flee by boat, and Volpus goes with them.
The metal monster drives through the sea of Mara toward Victris. There, the metal monster encounters the farmers of Daveli, who are under Keren’s command. The men of Daveli are knocked out by a sleep ray, and Keren too is examined by the metal monster. The metal monster heads toward Trigan City, but Keren takes a plane and warns Trigo. The Trigans attack the metal monster with aircraft led by Janno, but the metal monster disables one of the planes with its sleep ray.
Since they do not know how to deal with the metal monster, Peric advises waiting. Trigo decides to station an army of a thousand men outside the city gates to wait for the metal monster there. Inside the metal monster, non-materialized beings communicate with each other and decide to use their energy beam only if attacked. However, their energy is quickly running out, and they hope the Trigans can give them energy.
When the metal monster appears before the city gates, Trigo wants to give the signal to attack, but before he can do anything, all the soldiers fall asleep. Peric realizes that the yellow light from the metal monster is draining their energy. Trigo and Peric are seized by the tentacles of the metal monster and brought inside. There, they meet Sultar, who tells them that they come from Toxan.
Toxan is a planet located behind Elekton’s second sun and therefore can never be seen. The scientists of Toxan discovered the asteroid Gallas and were tasked with destroying it before it would crash into Elekton. The beings of Toxan are not humanoid and will fall apart if touched. However, they need some energy in order to take off in materialized form.
Outside the metal monster, Brag attacks it with a heat cannon. But Trigo speaks to him, and they stop. Sultar explains that after they landed on Gallas, they had engine trouble and could not leave before Gallas would crash into Elekton. Due to the great forces, the metal monster sank into the moon’s interior. The volcanic eruption allowed them to escape again. Thanks to the Trigans’ energy, they can now depart for Toxan.
Links
Plot summary (Dutch)