|HD 28185 b is the first exoplanet discovered with a circular orbit within its star's habitable zone.
Credit: STScI Digitized Sky Survey
The Oxford English Dictionary announced this week the latest new terms to bolster its role as the classic overseer of the English language.
As sandwiched between the new additions for 'arborist' (a tree surgeon) and the Indian term 'batchmate' (a classmate) is a new word hardly a decade old. Accepted this week to the dictionary is 'astrobiology', defined as 'the branch of biology concerned with the discovery or study of life on other planets or in space.'
Derivative forms are the adjective, 'astrobiological' and noun, 'astrobiologist'.
Counted among the Oxford entries in what has 'long been considered the ultimate reference work in English lexicography', the 20-volume compendium has declared officially that 'the search for life elsewhere' needs a definition.
Since astrobiology came into its own from the earliest international science gatherings, the usage of the term has been discussed.
One group of advocates considered whether astrobiology needed to be distinct from exobiology, an antecedent field that has occasionally been used as a synonym. Exobiology journals existed already and conferences discussed the origin of life or how microbes might survive in space. One distinction between the prefixes 'exo-' and 'astro-' centered on whether exobiology treated extraterrestrial life only and not broader issues of terrestrial climate or evolution on Earth as precursors to understanding life elsewhere. So would exobiology consider new methods of planet discovery, for instance, as being biological enough for their journals? Astrobiology journals seemed willing to fill any gaps, if a topic was somehow linked to the discovery of life elsewhere.
Other examples to distinguish the two branches might show themselves on an invited speakers list. An astrobiologist might be an invited speaker if they could reference geological research to determine the age of the Earth or track planetary evolution if it might help quantify the probability of finding another Earth-like world. An exobiologist seemed less likely to be a geologist or astrophysicist by training.
At those early meetings, another group questioned the literal interpretation of 'astrobiology' as meaning 'the biology of stars'. Was astrobiology about stellar reproduction? The question was posed half in jest, but might prove semantically troublesome, particularly if the Greek prefix 'astro', or 'stars', might mislead an international scientific community just being introduced to controversial issues in such a nascent and cross-disciplinary field. Few could argue that a fiery star itself was ever habitable, so labelling astrobiology as 'the biology of stars' had literal implications for introductory teachers, students and dictionary editors.
|Image of the Earth and Moon taken by the Galileo probe.
Academic writers, including a few now published by the Oxford University Press (OUP), have bandied around the term, astrobiology, as formally including 'the scientific search for life in the universe, and the current level of scientific understanding of how life begins, grows, and becomes intelligent in our Solar System and beyond.' The jacket cover on a 2002 OUP publication called astrobiology, 'one of the most exciting new fields in science'.
Whether the relation between the rising number of astrobiology courses-- and the textbooks to support those graduates-- has a bearing on its now popular usage is not clear, but as the oldest English-speaking university in the world, Oxford now seems willing to survey the field from the ground up. Ever since the European university system formally divided departmental responsibilities in science to the big three-- physics, chemistry and biology-- many cross-fertilizations like astrophysics and earth science have arisen to confound those divisions.
But few of these candidate disciplines can count such a wide array of practitioners as can the broad cadre of astrobiologists. Among them are included cosmologists, computer theorists, engineers, robotocists, geologists, radio astronoomers, organic and biological chemists. Given the rapid advances in the frontiers of genetics, no shortage of microbiologists and DNA experts have broadened their view of their own fields to include consideration of how the primordial soup might have been stirred elsewhere in the universe. One question in defining astrobiology remained: exactly what disciplines did it exclude?
A picture may help. Each scientific branch has its defining image. Physicists split the atom, chemists built the periodic table, and biologists have the DNA molecule. Should astrobiologists have a logo? Conducting a survey on the street might link astrobiology to alien searches. But as a discipline, astrobiology seemed less slanted towards a particular humanoid shape of an alien lifeform or even an enormous radio dish pointed skywards.
If such a vast field could be reduced to a single picture, then one candidate might be a picture of an ocean on another world. Just finding a great sea would imply biology to many, since as ingredients go, liquid water has preeminence in defining conditions suitable for life. Indeed, in looking back at our own planet from space--the "Pale Blue Dot"--Carl Sagan used the Voyager probe's photograph of Earth from over 3 billion miles to highlight both the vastness of space and the relative importance of water for life here.
In 1998, NASA's Associate Administrator Wesley Huntress, Jr., stated , "Wherever liquid water and chemical energy are found, there is life. There is no exception." A working definition for astrobiology therefore might evolve in practice to mean: wherever a source of water is found outside Earth, a curious astrobiologist is likely to be found lurking.
An alternative but less pictorial view of how a branch of science gets its definition relies on knowing its particular tools. In this view, a carpenter is known by his hammer and saw, not by the house he builds. Among the sciences, do astrobiologists have a characteristic method of measurement? Astrobiology of course inherits all the rich scientific timeline of instrument developments, but critics have wondered if any search for life could ever pass a statistical test. On a planetary scale, only one example of an inhabited world is known to us or even available to scientific conjecture.
This criticism is blunted if more new planets around other stars reveal themselves and as more extreme environments for life on Earth prove fertile. One hundred such new worlds have been identified just since the term astrobiology came into NASA usage. If any natural phenomenon can be measured, it can safely be bet on to enter the wider halls of science. So the argument goes according to advocates and pioneers in the field, astrobiology has too many many things to measure, not too few. After all, if twenty-five percent of all stars also host a larger solar system of their own, then current estimates for the number of planets just in our own galaxy may top one billion yet undiscovered worlds. Beyond the semantics, few would argue the search for life lacks frontiers to explore.
One key to taking the next step in measurement for astrobiologists in fact is another of this week's new entries in the Oxford English Dictionary: the word, 'bioindicator'. The term refers formally to an organism used as an indicator of the quality of an ecosystem. So coincidentally, the roots of astrobiology may deepen as a discipline if more bioindicators are explored on Earth and elsewhere.
This week's entry of the term 'astrobiology' in the Oxford English Dictionary is laudable to scientists who debated its earliest boundaries. Few students may actually rely on a dictionary to describe a branch of science, but the event itself symbolizes a coinage that is likely to outlast just a single generation of graduates. As with any working science, ultimately the field is defined by the topics of research treated in its journals and conferences. Indeed a popular topic among SETI researchers addresses how best to communicate with another civilization, when we cannot assimilate each other's meanings--or even new usages of shared Greek roots like astro- and -biologia.
In the world of new words, astrobiology appears poised this week to become another word for finding new worlds.
Related Web Sites
NASA/Ames Pale Blue Dot Workshop Proceedings
Visible Earth: NASA Pale Blue Dot Imagery
Planet Quest (JPL)
Frequent Wet Earths?
Entropy and Evolution
What is Life?
Life's Working Definition