WEDNESDAY, 3 OCTOBER 2012
Democritus, the ancient Greek philosopher, famously stated that the world was composed of atoms and empty space. Despite his speculation no further advances were made in atomic theory for almost two thousand years until the turn of the 20th century when a number of key experiments provided the evidence to prove his assumption. As the field of atomic theory shows, without data even a correct hypothesis cannot advance.The same is true for astrobiology, the study of life elsewhere in the Universe. The speculation that we are not alone in the Universe is as old as human civilization itself, and indeed Democratus himself believed it to be true. But, while the question of whether life exists on other planets is a verifiable hypothesis, it is one that is difficult to test, and progress in the field has been slow.
Despite the musings of various authors, philosophers and film directors on the subject, astrobiology as a science has only been around since the second half of the last century. Three major developments prepared its way. The first was the development of rocketry, given huge momentum by the Second World War and the Cold War. The second was radio astronomy. The third, and most important, was the experiment of Stanley Miller and Harold Urey. Combining water, methane, hydrogen and ammonia, and adding a spark, they found that amino acids, the building blocks of life, were formed. Knowing the conditions under which life may have begun on earth allowed the search for those conditions elsewhere.
In 1957, the Soviet Union launched Sputnik 1 into orbit, and the Nobel Laureate Joshua Lederberg went to Calcutta to visit the evolutionary biologist J.B.S. Haldane. Discussing the recent Soviet triumph, the two men agreed that if Sputnik were to land on the moon, it would carry with it microorganisms from Earth which would irreversibly contaminate the lunar surface. On his return to the United States, Lederberg wrote a series of memos that warned of possible contamination and the importance of sterilising all possible spacecraft thoroughly. At the time he suggested that the moon might be covered with organic precipitates of the kind that it was now clear could give rise to life. Though the possibility of terrestrial contamination of the moon remained an academic subject, the possibility of extra-terrestrial contamination of Earth captured the public imagination, with headlines like “Space Academy Board Warns of Microbe Attack from Space”.
At the time, NASA administrator Dan Goldin predicted that the addition of biology to astronomy would lead to screaming from the physical scientists, but biologists were similarly sceptical. G.G. Simpson, one of the most significant palaeontologists of his time, dismissed astrobiology as a haven for ex-biologists. The next two years saw a boom-time, with many Nobel Laureates and Carl Sagan, a prominent astrophysicist, joining the field. Without these scientists astrobiology might not have begun, as it is still often criticised as a “science without a subject,” a criticism first made by Simpson.
Fuelled by the Cold War, funding poured into rocketry. The moon was found to be barren, but Mars was a richer target. The first Viking missions carried with them tools to search for microbial life there. While they identified carbon dioxide produced from a nutrient broth, it was later found to be the result of a non-biological chemical reaction.
Following this disappointment, astrobiology entered a lull phase, having exhausted the available sources of data. Yet it was during this lull that the fundamentals for its renaissance were being put in place by developing new avenues of inquiry. Scientists began searching extreme enviroments on Earth in the hope of finding life thriving in conditions similar to those of other planets.
In 1977, the deep-sea exploration submersible Alvin found life clustering around volcanoes 2.5 km below the surface of the ocean, providing a demonstration that life can exist in the absence of the sunlight, something of particular importance when imagining life on the outer planets. Moreover, in the conditions of volcanoes, dissolved meteorite could yield some of the building blocks of life - probably a common occurrence in the volcano and meteorite rich early history of Earth.
This was further helped by another breakthrough in the search for the origin of life. Up until this point, the question of the first molecules had always faced a paradox. The first molecules could not be proteins, as proteins cannot be formed without the cellular instruction manual, DNA. Neither could the first molecules have been DNA, as DNA is meaningless without protein to turn its message into something usable. The answer came in the 1980s, when a new class of RNA molecules, Ribozymes, were discovered. Ribozymes have both the ability to carry information, like DNA, but like proteins they can perform chemical reactions. Indeed, investigators studying the origins of life have produced ribozymes that are capable of self-synthesis. The idea that ribozymes have the ability of both carrying information and acting on it, provided a missing link between the dead world of pure chemicals and the first cells. Work immediately began looking for variations that could arise on Earth and in space.
The field was set for a full renaissance, and it got one 1995 when 51 Pegasi b, the first planet orbiting a Sun-like star, was found. Further successes followed in short order. In the same year, NASA launched the Infrared Solar Observatory, which has discovered organic molecules in comets and cosmic dust: hardly unimportant since even our atmosphere-protected planet accumulates between fifty and a hundred tonnes of extra-terrestrial matter a day. Meanwhile the spacecraft Galileo returned suggestions of an ocean of liquid water beneath the ice of Jupiter’s satellite Europa. The work on undersea life clustering around volcanic hotspots without other sources of heat and energy took on new significance. The next year a Martian meteorite retrieved from Antarctica, ALH 84001, proved to contain possible nanobacterial fossils, although this discovery was controversial and many believe that the bacteria may have origionated on earth.
In the almost two decades since these momentous discoveries, two major journals have been founded dedicated to astrobiology, NASA has unveiled a roadmap to cover the next several decades of research, and the European space agencies have become involved. At each stage of the process of emerging from speculation to science, astrobiology has been firmly guided by the data, and it is on this solid base that it is set to succeed in the future. Further missions are planned with the European Space Agency’s ExoMars and NASA’s Red Dragon both destined leaving for Mars in 2018. This summer, the rover Curiosity landed on Mars, to begin its investigation of the habitability of Mars. There are already over 800 extra-solar planets discovered, with the rate of finding growing ever more rapid. From empty speculation to sound science, astrobiology’s future is secured.
Hugo Schmidt is a 4th year PhD student in the Department of Biochemistry
