World governments should prepare a co-ordinated action plan in case Earth is contacted by aliens, according to scientists.

They argue that a branch of the UN must be given responsibility for "supra-Earth affairs" and formulate a plan for how to deal with extraterrestrials, should they appear.

The comments are part of an extraterrestrial-themed edition of the Philosophical Transactions of the Royal Society A published today. In it, scientists examine all aspects of the search for extraterrestrial life, from astronomy and biology to the political and religious fallout that would result from alien contact.

"Will a suitable process based on expert advice from proper and responsible scientists arise at all, or will interests of power and opportunism more probably set the scene?" asked Professor John Zarnecki of the Open University and Dr Martin Dominik of the University of St Andrews in the introductory paper. "A lack of co-ordination can be avoided by creating an overarching framework in a truly global effort governed by an international politically legitimated body." The pair argue that the UN has a ready-made mechanism for such a forum in its Committee on the Peaceful Uses of Outer Space (Copuos).

Member states of Copuos should put "supra-Earth affairs" on their agenda, say the scientists, and establish structures similar to those proposed for dealing with threats from near-Earth objects, such as asteroids, that might be on a collision course with our planet.

According to Simon Conway Morris, a professor of evolutionary palaeobiology at Cambridge University, anyone planning for alien contact should prepare for the worst.

Evolution on alien worlds, he said, is likely to be Darwinian in nature. Morris argues that life anywhere else in the universe will therefore probably have important similarities with life on Earth – especially if it comes from Earth-like worlds that have similar biological molecules to ours. That means ET might resemble us, warts and all, with our tendencies towards violence and exploitation.

"Why should we 'prepare for the worst'? First, if intelligent aliens exist, they will look just like us, and given our far from glorious history, this should give us pause for thought," wrote Morris in the journal's special issue.

Ted Peters, a professor of systematic theology at the Pacific Lutheran Theological Seminary in California, considered what might happen to the world's religions in the event of ET making contact. Conventional wisdom suggests that terrestrial religion would collapse if the existence of extraterrestrial intelligence (ETI) were confirmed, he wrote.

"Because our religious traditions formulated their key beliefs within an ancient world view now out of date, would shocking new knowledge dislodge our pre-modern dogmas? Are religious believers Earth-centric, so that contact with ET would de-centre and marginalise our sense of self-importance? Do our traditional religions rank us human beings on top of life's hierarchy, so if we meet ETI who are smarter than us will we lose our superior rank? If we are created in God's image, as the biblical traditions teach, will we have to share that divine image with our new neighbours?"

His conclusion, however, is that faith in Earth's major religions would survive intact. "Theologians will not find themselves out of a job. In fact, theologians might relish the new challenges to reformulate classical religious commitments in light of the new and wider vision of God's creation."

"Traditional theologians must then become astrotheologians ... What I forecast is this: contact with extraterrestrial intelligence will expand the existing religious vision that all of creation – including the 13.7bn-year history of the universe replete with all of God's creatures – is the gift of a loving and gracious God," he speculated.