Anybody out there? The how and what of alien life

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Artists' impressions of Pluto are all we have until a probe reaches it in 2015 (Image: ESO/L. Calçada)


Three new books bring us up to speed on extraterrestrial life, its prospects and possible forms – but it remains "queerer than we can suppose"


THERE are some 100 billion galaxies in the observable universe, with about 100 billion stars in each of those galaxies. And in recent years, we have discovered that there are probably more planets than there are stars. In fact, there are more planets in the universe than there are sand grains on all the beaches of all the coastlines of all the continents. Yet, in all this immensity, there is only one place where we know there is life – the tiny, fragile "blue dot" we call Earth.


This rather handicaps our speculations about life elsewhere. Not that you would know it, to judge by the hundreds of books published every year about extraterrestrial life, its prospects and possible forms. Some are exuberant and ambitious in scope, other pure entertainment, and still others modest and fact-based.


Luckily for me, three new books combine most of the elements above – to varying degrees. First up is From Dust to Life: The origin and evolution of our solar system, by planetary scientist John Chambers and writer Jacqueline Mitton. I recently built an app about the solar system, and my research would have been made a lot easier if I had possessed a copy of this excellent book. It provides a truly comprehensive overview of our solar system's origins and is written in plain, jargon-free language.


As the title suggests, Chambers and Mitton begin with dust particles coagulating in a protoplanetary disc around the newborn sun – pointing out that an unsolved mystery is just how dust grains grew into mountain-sized "planetesimals". They go on to explain the origin of the disparate bodies in the solar system, from rocky planets like Earth to gas giants like Jupiter, from asteroids to Kuiper belt objects.


We are at the dawn of a golden age of planetary exploration. Although we have stunning images of most of the planets and large moons, we have barely begun to document what is out there.


Chambers and Mitton describe how the NASA probe New Horizons is due to fly by Pluto at a distance of 10,000 kilometres in July 2015, and perhaps most excitingly, that the Rosetta probe, sent by the European Space Agency (ESA), is due to go into orbit around Comet 67-P/Churyumov-Gerasimenko in November 2014 and deploy a lander with a drill to sample its interior.


The hope is that Rosetta will prove as useful at unravelling the mysteries of the past as the Rosetta Stone in Egypt. But these mysteries go back to the dawn of time: by sampling what may prove to be pristine material from which the solar system formed 4.6 billion years ago, Rosetta may help us decode the message recorded in the comet's nucleus, thereby shedding light on the origin of the Earth and the other planets.


If space means extraterrestrial life to you, however, then that's well covered in Life Beyond Earth: The search for habitable worlds in the universe by French astrophysicists Athena Coustenis and Thérèse Encrenaz. The authors consider the best places to find life in our solar system to be Mars, Jupiter's moons Europa and Ganymede, and Saturn's giant moon, Titan.


The big surprise has been tiny Enceladus, Saturn's sixth largest moon, which has ice fountains spewing into space and an internal ocean. The message seems to be that we should be looking even more widely for life-bearing bodies.


Coustenis and Encrenaz make a good case for Europa being second only to Mars in its potential for hosting life. The 100-kilometre-deep ocean beneath the surface of Europa is believed to rest on rock, rather than ice as on the other giant moons, Ganymede and Titan.


This raises the tantalising possibility of volcanic vents spewing chemicals into the water. On Earth, such vents support complex ecosystems of sulphur-eating bacteria and arm-length tube worms. Might they do the same on Europa? Unfortunately, we will have to wait for the Jupiter Icy Moons Explore (JUICE) probe, which ESA hopes to get to the Jovian system in January 2030.


In their thorough and entertaining book, Coustenis and Encrenaz also discuss the prospects for life on the 800 or so planetary systems so far discovered around other stars. In 2011, the planet Kepler-22b was discovered 600 light years from Earth and in the habitable zone of its star. But the reality is that finding life in such remote locations is going to be hugely more difficult than in the cosmic backyard of our solar system.


Let's face it, though, the big question for most of us is not whether there is a second biology out there in the shape of microorganisms, plants or animals, but whether there are aliens we can actually talk to. This is a subject of particle physicist Don Lincoln's Alien Universe: Extraterrestrial life in our minds and in the cosmos.



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Issue 2950 of New Scientist magazine


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