Dr Boss (and his students must love that name) reckons the aliens must be out there because of “the new belief that there is an abundant number of habitable planets like Earth” – according to the article, there could be “100 billion trillion Earth-like planets in space”. The most interesting bit – why this “new” belief has come about – is entirely absent from the article, so all we get is a retread of the old “well, if there are so many planets out there, there must be life on some of them!” routine. That argument may hold some water (if you’ll excuse the pun, which you’ll get as you read on), but as I’ve been reading in What Does A Martian Look Like? (Jack Cohen and Ian Stewart, Ebury Press, 2002; I’ll be talking more about it on my book blog) this is the least interesting reason to believe life is out there.

The standard idea in astro-biology is that life can exist on planets in the “habitable zone” around a star: that is, the range of orbital distances in which the temperature variation allows water to exist as a solid, liquid and gas. This is rubbish for a number of reasons, not least the fact that the existence of water in various forms is dependant on a vast number of things beyond just a planet’s distance from the star. In our own solar system, now that Mars has proven barren, Jupiter’s moon Europa is the most likely candidate for extra-terrestrial life, with it’s liquid ocean safe below the huge ice-sheets on its surface.

But that’s assuming you even need water for life to exist. And why should you? Just because Star Trek and Star Wars prefer aliens who look like humans with ill-conceived cosmetic surgery or anthropomorphic animals, it doesn’t mean that’s what life will look like. Stewart and Cohen argue that astro-biology is really just the application of Earth-based biology on other planets. It’s parochialism on a grand scale; the galactic equivalent of travelling the world but spending the whole trip in “Irish” pubs and eating at McDonalds.

How do we get past this? Jack&Ian (this is how they refer to themselves in the book) say we need a new discipline, “xenoscience”, to properly consider what aliens will be like. An essential ingredient of xenoscience is imagaintion, and in a sense this is where science fiction, or at least the popular kind – where the “science” really translates to “physics buzzwords and folk biology as window dressing on a fantasy story” – has failed us. Yes, some authors have thought about what life might really be like, but mostly the point of an “alien race” is just to act as a stand-in for some aspect of human culture. For my money, the biggest proof of this is that no-one stops to think about what it really means to have half-human half-Vulcans. Even if alien life did, impossibly, look very similar to us, it doesn’t mean we can shag it, marry it or build a picket fence and have 2.4 children with it; that people accept this in Star Trek is a clear sign they don’t really think of Vulcans, Klingons and the rest of them as truly alien; I’m sure if you suggested the same sort of “first contact” or “close encounter of the fourth kind” with a more realistic ET, you’d probably be blocked by the Great Australian Internet filter.

I’m not quite finished the book, so I can’t tell you what Jack&Ian reckon a Martian would look like. But whatever life does exist out there, odds are it will be incredibly unfamiliar to us; truly “alien”. If we’re to recognise it when we see it, let alone have any chance of conversing with it, then we need to embrace the imagination we have. Imagining something doesn’t make it possible, but science is about change, about difference, and about possibilities. Often it works by eliminating possibilities – but we can’t eliminate them if we don’t at first consider them.