In the heavens, as it is on Earth

Proof of the existence of extraterrestrial life may be closer than we think, thanks to a surge of research in astrobiology. Lewis Dartnell is determined to ascertain that we are not alone

十一月 19, 2009

There is a bright new science flourishing in the UK; a science with bold hopes to understand the origins of life on Earth and where else it may exist in the cosmos. It's called astrobiology, and I'm just beginning my research career in this promising new field.

Perhaps it's a little unfair to imply that astrobiology is completely novel: after all, Nasa was sending life-detection experiments to the surface of Mars back in the 1970s. But these early attempts at finding extraterrestrial life resulted in disappointment and a slump in interest in astrobiology for the three decades since. Now, however, bolstered by new discoveries across the breadth of research it encapsulates and a renewed acceptance and enthusiasm for the subject within the scientific community, astrobiology is enjoying a resurgence.

This reignition of interest has been triggered by developments in several diverse areas. Our recent exploration of the solar system has revealed a gamut of extraterrestrial locations that are thought to provide the basic requirements for the sustenance of life, from water seeping out of gullies on Mars to the deep ocean hidden beneath the icy face of Jupiter's moon Europa and the frigid methane rivers and lakes of Saturn's moon Titan. Even one of the hitherto ignored minuscule moons of Saturn is now thought to have subterranean caverns full of water.

Peering beyond our own cosmic back garden, in the past 14 years astronomers have discovered more than 400 planets orbiting other stars in the galaxy, several of which may support oceans of water suitable for life. The announcement of the discovery of the first truly Earth-like world is realistically expected in the next few years, and astronomers are also confident that before too long we'll have the capability to detect evidence of life in the make-up of its atmosphere.

Another important emerging realisation of astrobiology is that, while perhaps life itself cannot be transported between the stars to seed young worlds, many of the essential molecules certainly are extraterrestrial. The organic building blocks of life would have rained down in meteorites upon the young Earth like manna from heaven. Just last year, a research group at Imperial College London found components of DNA, called nucleobases, in a space rock. These vital building blocks could have been incorporated into the genetic coding of the earliest life forms on our planet.

Perhaps the most astounding discoveries are the vast range of hostile environments on Earth that have been found to support hardy life forms. It almost seems as if every moist nook or cranny on the planet that biologists think to check is found to be teeming with life: from boiling acid volcanic pools to near-freezing pockets of brine beneath miles of solid ice. These ultra-hardy terrestrial organisms could survive the conditions that may be found in many extraterrestrial locations. I use such "extremophiles" in my research, including hardy bacteria I've isolated from the exceedingly cold and dry wastelands of Antarctica as well as a microbe called Deinococcus radiodurans. This remarkable organism has been reverentially dubbed "Conan the Bacterium", on account of its astounding ability to survive many different hazards, including radiation doses thousands of times higher than that which is lethal to humans.

The growing acceptance of astrobiology is being mirrored by increased media coverage and public interest in the field. Recent news stories have focused on the salty seas within Saturn's moon Enceladus, the launch of the Kepler space telescope able to spot Earth-like planets orbiting distant stars, and the observations of methane gas in the Martian atmosphere. My own work focuses on Mars and the energetic radiation streaming down on to its rusty-red surface from space, unleashed by violent cosmic events such as solar flares or exploding stars throughout our galaxy. Here on Earth, we're protected from these cosmic rays by a deep atmosphere and the magnetic deflector shield that cocoons our planet. The key question is how these cosmic rays would affect the survival of microbial Martian life or our ability to detect evidence of its past or present existence. But this is just one tiny facet of the burgeoning field.

A national survey published this year in the journal Astrobiology found 33 astrobiology research groups in Britain, involving almost 290 researchers ( There are now also 15 university courses involving astrobiology, with an enrolment of 880 students every year. The sheer diversity of astrobiology research represented is staggering. There is biochemistry and the molecular origins of life, microbiology and the study of the hardiest life forms on Earth, geology and the detection of signs of life in the most ancient rocks on the planet, planetary science and the factors necessary to keep a world habitable, and astrophysics and the detection and characterisation of planets orbiting distant stars. This is without mentioning the industrialists and engineers employed by UK companies to build the next generation of robotic space explorers designed to hunt down signs of life on other worlds.

ExoMars, for example, is a European Space Agency mission due for launch in 2018. It will carry a suite of sophisticated instruments to test the red planet for the presence of organic molecules and evidence of the prior existence of life. My department at University College London, the Mullard Space Science Laboratory, is leading the construction of ExoMars Rover's robotic eyes. This PanCam system will combine twin cameras to allow the probe to see the planet around it in three dimensions, just like our own eyes do, and a paparazzi-esque telescopic lens for really zooming in on sites of potential interest and scrutinising the soil that is brought up by ExoMars' drill. It's this soil from deeper beneath the Martian surface that holds the best chance of revealing signs of life. One idea we're working on for a quick and easy way of spotting organics is to get them to glow in the dark with an ultraviolet light, like a gin and tonic in a nightclub.

One of the greatest joys of astrobiology is the enormous range of diverse subjects it encompasses; it is deeply interdisciplinary. At present it seems the community is more "astro" than "biology". The underlying reason is not immediately clear. Is it that physics and astronomy departments have been more proactive in establishing astrobiology research themes or taught courses for their students, whereas biology students, for example, are lacking in opportunity? Or perhaps is it that biologists do have open access to such courses but are less willing to leave their academic comfort zone and learn about the physics and astronomy aspects of astrobiology? This broad reach can mean that researchers struggle to secure funding, with projects falling between the cracks in the remits targeted by the research councils. The Science and Technology Facilities Council has shown leadership in supporting astrobiology, funding research fellowships as well as the UK involvement in the ExoMars Rover. In fact, the UK is the second-largest contributor, after Italy, to the design and construction of this mission.

As well as carrying with it hopes for discovering signs of Martian life, ExoMars promises a good many benefits back home. For example, the technology used in one of the life-detection instruments has been applied to the extraction of petroleum from rocks and to the processing of "heavy oil", replacing hazardous and expensive solvents with safe, clean alternatives.

"Are we alone?" is a question that has been asked by humanity across the millennia, and we may now not be too far from answering it. There is real optimism that our robotic probes or astronomical surveys could find irrefutable evidence of alien life within our own lifetimes. We've just got to go out looking for it.



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