OAS NOVEMBER 20013 ASTRONOMY EZINE VOL 2 | Page 38

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Not so many years ago it
was a common occurrence
that if you mentioned an
interest in astrobiology to
a gathering of scientists you’d be met with raised eyebrows, polite coughs, and sympathetic noises. The
science of ‘life in the universe’ has had a rocky path to follow.
There was good reason for skepticism. As much as people could agree that the fundamental questions of
astrobiology were incredibly interesting – tackling such tasty morsels as life beyond the Earth, life’s origins, and the cosmic significance of life – they could also agree that meaningful answers were a long way
off. A sample size of ‘one’ presents a steep challenge.
Times have changed though, and perhaps the most profound shift in this scientific endeavour has come
from the ‘astro’ part of astrobiology in the past couple of decades. Before the 1990’s professional astronomy had more than its fair share of planet-hunting corpses littering the landscape. As far back as in the late
1800’s, claims of planets in places like the 70 Ophiuchi system (a binary some 16.6 light years away)
were quickly refuted. In the 1960’s and 1970’s claims of planets around Barnard’s Star received a confusing mixture of support and devastating criticism from different sides of the astronomical community.
These efforts were pushing the boundaries of feasibility. Some relied on micrometre-level measurements
of stellar motion on photographic plates, a tricky enough thing made even more so by error sources such
as unreported equipment realignment and well-meant cleaning. It was not a happy situation.
By the 1980’s it was only a few very dedicated, and brave, professional astronomers who carried on, developing spectroscopic techniques for sensing the Doppler shift of light from stars that might be wobbling
around a common center of mass with unseen planetary companions. But believable detections of planets
were thin on the ground, and it was only in the 1990’s that a quick succession of discoveries began to
transform the field. First was the detection of planetary mass bodies around a pulsar, and close behind
came the first truly robust evidence of a giant planet tightly orbiting a sun-like star.
Flash forward nearly twenty years and we’re awash in planets. Close to a thousand confirmed worlds now
adorns the public listings, and my colleagues assure me that the database of NASA’s Kepler mission almost certainly contains 3,000 more bona fide objects awaiting the seal of approval. Extrapolating the statistics tells us that there must be billions of planets roughly the size of the Earth in our galaxy that are also
orbiting their parent stars at distances where a temperate surface environment could exist. In fact, some
analyses posit that a ‘habitable’ world ought to exist around one of the low-mass stars within about 16
light years of us, with a ninety-five percent statistical confidence.
This is one of the turning points for astrobiology, I think it could perhaps be the biggest. Now we actually
know that it’s reasonable to ask questions about life on other worlds because there are other worlds in
abundance, and some should be pretty close by. These provide tempting targets for the next generation of
telescopic instruments, from NASA’s budget-crippling-but-amazing JWST, to the new 30-metre class observatories that are slowly moving from drawing board to mountaintops.
JWST may be able to detect molecules like water and carbon dioxide in the atmosphere of a transiting
Earth-sized planet around a nearby low-mass star. The great ground based observatories may complement
this with an ability to spot oxygen. And all such instruments, together with observatories like the millimeter and sub-millimeter sleuthing ALMA, should reveal other properties of exoplanetary systems, such as
the presence of zodiacal dust and its progenitor asteroids and comets that may provide important clues to
the planetary environments.

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