Where is Everyone? The Fermi Paradox, Astrobiology and Exoplanets

Since the middle of the last century, against the backdrop of greatly expanding space technology and understanding, scientists have wondered about our place in the vast universe and whether we are alone or not. When it comes down to it, why would we be? There is no reason, be it physical or chemical, life couldn't exist elsewhere. At first glance it seems that we live on a relatively normal planet, our parent star is of a fairly common variety and our corner of the galaxy isn't all that extraordinary. Water and other 'building block' organic compounds, thought crucial for life in any imaginable form, are relatively abundant throughout the galaxy.

There are at least 100 billion (that's a 1 followed by eleven zeroes) stars in the Milky Way galaxy; many we now know come complete with a family of planets in their orbit. On top of that, several of these newly-discovered 'exoplanets' (that's the name for a planet outside our solar system) are not that different from the Earth in mass or orbital distance from their parent stars. In fact, a recent study calculated that a staggering 17 billion Earth-like planets are likely to exist in the Milky Way alone! Surely, more than one of those worlds would have life of some kind or the other clinging to its surface? And if there was life, even if it was almost vanishingly rare, could another species with a similar level of intelligence to humans exist on another one of those billions of planets out there in the reaches of space?

 

Artist's impression of Gliese 667Cc, a possible Earth-like exoplanet 22 light years distant, in the constellation Scorpius. 

Credit: ESO/L. Calçada

Given that a multitude of habitable worlds exist, many covered in a primordial cocktail of complex, biologically useful compounds, it seems that the Milky Way should be teeming with life. So, where is everyone?  This question has proved tricky, paradoxical even. Accordingly, it's known as the Fermi Paradox after the Italian astronomer who first posited the riddle to the wider scientific community, where it was met with unexpected consternation. Over 50 years on and it remains a question without an answer. SETI pioneer Frank Drake devised an equation to address the problem, which Things We Don't Know blogged about in October 2012, called the Drake Equation, which attempts to provide an estimate of the likely number of other civilisations in the Milky Way. However, the huge uncertainties involved in each stage of the calculation limits its predictive powers to more of an interesting thought exercise than a robust scientific methodology.

What does this apparent silence say about us and our planet? Are we the product of an extremely fortunate evolutionary accident resulting from the interplay between our astronomical and planetary environment? On some distinguishable level, the search for other intelligent species is a thinly veiled search for our own place, both physically and philosophically and convincing proof of a co-existent alien civilisation would most likely have significant scientific, social, political and religious ramifications.

Today, researchers in the burgeoning scientific field of astrobiology attempt to tackle these kinds of open questions, as well as many others in disciplines spanning chemistry and geology, astronomy, biology and even economics and the social sciences. In my completely biased opinion, studying exoplanets is one of the most exciting areas of science to be working in right now, and the rate of new advances and discoveries are progressing at breakneck speed (for science, anyway). However, even despite these recent findings, our understanding of the processes operating on these planets remains regrettably threadbare. Given the immense distances involved and sensitivity required, only limited data is available for a given planet and some large uncertainties remain even when information has been collected. We have yet to image an exoplanet directly, and it may be decades before the technology is available to do so.

Despite the difficulties involved, a picture of our planetary neighbours is beginning to emerge and the results have been surprising and exciting in equal measure. Over the course of several posts for Things We Don't Know, I'll do my best to illuminate the cunning techniques that are being used to tease exoplanet data out of the noise, and explain how the limitations of contemporary technology are driving the development of new methods of remote planetary investigation.

This article is by Andrew Rushby, currently undertaking a PhD in earth systems modelling at the University of East Anglia. Andrew usually blogs at the II-I- blog, the Pale Blue Blog or the European Association of Geochemistry blog. He can also be found launching high altitude balloons into (near) space, and tweeting as @andrewrushby. This is the first in a series of posts about the many unknowns involved in the study of planets which orbit other stars across the galaxy.