The Science of Life in the Universe
Astrobiology - it is an ambitious field with collaborations that cross international and disciplinary borders. Until recently its influence on science fiction tarred its practitioners with the same melodramatic brush. It has only been since the discovery of the first planets outside the solar system in the mid-1990s that the field has progressed towards the mainstream. The European Space Agency (ESA)’s ‘Cosmic Vision’ for space science in Europe places it first on the agenda, asking “What are the conditions for planet formation and the emergence of life?”. NASA’s high profile Spirit, Opportunity and Phoenix rovers were designed to identify potential organic material and feedstock in the Martian soil, while their cousins Mars Express and Mars Odyssey scoured the surface from orbit, searching for water. Looking further afield, the Kepler Space Telescope, launched in March, will scan 100,000 stars in an attempt to detect Earth-like planets.
Astrobiology is the progeny of work in the early 1960s, when Frank Drake first wrote down the now-famous Drake Equation (which calculates the multiplicity of intelligent civilisations in our galaxy) at the Green Bank meeting in West Virginia. It began a concerted effort to legitimise the study of intelligent life and hold it up to the light of bona fide scientific inquiry. As the years have progressed it has become clear that astrobiology, once named exobiology, is not merely biology or astronomy; it is a culmination of all the sciences.
Firstly, physics and astronomy are needed to describe how stars and planets are formed. This requirement was illustrated by the first planet discovered around a sun-like star. Designated a ‘hot Jupiter’, it is a gas giant planet that orbits much closer to its parent star than even Mercury does around our sun - so close that its daylight temperature is 2000ºC. This was a revolutionary discovery and put paid to traditional assumptions that our solar system was typical and that gas giant planets belonged in the outer suburbs. The discoveries that followed continued to surprise. Hot Jupiters and other exotic planets were common amongst the crop. Of course, the instrumental sensitivity required to observe a solar system like our own was well beyond the abilities of observers fifteen years ago. As our instruments improve and more planets are detected, we are discovering that neither hot Jupiters nor solar system analogues are the norm. Planetary systems display such a rich and diverse architecture that they challenge astronomers to explain them.
Secondly, we require chemistry to identify how the ingredients of life come into existence. Carbon, hydrogen, oxygen, nitrogen and phosphorous are but a handful of the essential chemical elements that form the organisms that inhabit the Earth. To understand life’s origins it is vital to understand how elements are created and how they form the molecular building blocks of organic material. Elements are forged in the searing furnaces of stars where the unfathomable temperatures and pressures in the stellar core facilitate the fusion of hydrogen atoms into helium atoms (and helium atoms into carbon and heavier atoms) and released into the void when a star ends its life. The carbon in your body exists because a star has died.
Finally, biology has the unenviable task of describing the origin and evolution of all life. This task is complicated by the fact that life itself is difficult to define – some definitions include fire as living, others exclude viruses (believed to be one of the earliest forms of life). ‘Entities that replicate and evolve by Darwinian evolution’ is usually taken to be the mainstream definition but it is argued that computers could eventually satisfy this criterion. If we are to go further and study intelligent life, we require the social sciences - anthropology, sociology, psychology, linguistics - to explain and understand the equivalent of the human condition and elucidate the mind of an alien.
Astrobiology is an exciting, young research field, with much virgin ground to be covered. Scientists from all disciplines can make a valuable contribution to the field and the benefits go in both directions. As a platform for scientific dialogue, astrobiology offers a chance for disparate fields to communicate, form new connections and collaborations, present new solutions to old problems and old solutions to new problems. Add to that its substantial ability to capture the public imagination and engage young people, and it becomes a means for science and the public to reconnect. This is of utmost importance if we wish to encourage the scientists of tomorrow.