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