Zeta Minor

Zeta Minor was the planet farthest out in the known universe. It contained a link to a universe of anti-matter.

Characteristics
Zeta Minor had a jungle-like terrain and was home to the anti-matter creature. Professor Sorenson believed that the planet was alive and, as he told Baldwin, that it "[watched] every move they [made]." The surface was divided into sectors for the purpose of designation.

Salamar described its location as being "beyond Cygnus A", "as distant again from the Artoro galaxy as that galaxy [was] from the Anterides. [It was] on the very edge of the known universe." (TV: Planet of Evil)

History
In the year 37166, Professor Sorenson led an eight-man expedition to Zeta Minor in search of an alternate power source that would save the Morestran civilisation.

When they found the first high quality strain, the expedition began to suffer from casualties - Lorenzo was the first - and the strain was found to have vanished. Sorenson believed the planet had "taken it back".

While in sector 5, Sorenson and Baldwin came across a vein with over seventy percent purity. The professor was unwilling to leave, despite the approach of nightfall, lest the vein should vanish again. At the expedition base, Braun was killed by the anti-matter creature. Baldwin returned to the base alone and, finding himself under attack, pressed the automatic distress button before he too was killed.

The Fourth Doctor and Sarah Jane Smith came to Zeta Minor in response to this signal, landing shortly before a Morestran probe ship began orbiting the planet. This ship was captained by Controller Salamar, who rejected Vishinsky's request for a low level scan of the planet in order to conserve fuel and ordered him to take a party down to the surface.

Sarah soon found the planet to be having a strange effect upon and felt as if "her mind left her body". Finding the dessicated corpse of Braun, the product of the anti-matter creature, the Doctor thought they must have landed months too late.

The Morestran party send the Doctor's TARDIS up to their ship before the ship itself landed on Zeta Minor. The Doctor and Sarah were both take prisoner and charged with the recent murders. (TV: Planet of Evil)