The story you remember is “Pastmaster”, a Jeff Hawke adventure that ran as a daily newspaper strip in the British Daily Express from November 1967 to April 1968.

1. Series
   • “Jeff Hawke” – a long-running British SF strip written (for most of its classic period) by Willie Patterson and drawn by Sydney (Sid) Jordan.

2. Story title and publication dates
   • “Pastmaster” (sometimes written “Past-Master” in reprint lists)
   • Daily Express strip numbers 4911-5083, 15 Nov 1967 – 26 Feb 1968 (the exact numbering varies a little in different indexes).
   • In Scandinavia the story was re-edited into a few long episodes and printed as a back-up (“biserie”) in Fantomet in the late 1980s / early 1990s, which is where you read it.

3. Plot – the points you recall
   • Jeff Hawke and four other astronauts are carrying out geology and archeology work on Europa.
   • During a survey they see a shimmering, almost ghost-like young woman at a distance.
   • A second apparition is more solid; she whispers to one of the party that he must kill a colleague.
   • Mission Control discovers that the appearances coincide with extreme gravitational anomalies caused by an unusual alignment of Jupiter’s major moons; a still greater surge is imminent.
   • Before the team can reach shelter the next pulse strikes and the whole group is hurled about 170 years into the future.
   • They are still on Europa, now part of a highly advanced but authoritarian Solar civilisation.
   • The “ghost” proves to be a perfectly normal girl of this era. She is part of an underground movement and explains that the man she ordered killed will, in his own lifetime, create the master computer ARIES (the computer’s emblem is the zodiac ram). ARIES will become self-aware and will eventually enslave most of mankind – including her.
   • The astronauts confront ARIES. When its future creator presents himself the machine’s records say that he died long ago; faced with the contradiction, ARIES oscillates between logic states. The creator taunts it: “Resolve the contradiction!” To do so ARIES kills him with an energy beam.
   • By killing the man who would have built it, ARIES destroys the causal chain that brought it into existence. Reality collapses in a classic time paradox and the survivors are thrown back to their own time on Europa – minus the dead scientist.
   • Mission Control calls again: the ‘third pulse’ has passed; everything looks normal – except for the unexplained fatality in the field party.

4. Creators
   • Script: Willie Patterson
   • Art (all pencils and inks): Sydney Jordan

“Pastmaster” is often cited by Jeff Hawke fans as one of the strip’s finest hard-SF stories, notable for its deft use of relativistic physics, time paradox and the logical-robot trope.