TEDGlobal: Dimitar Sasselov and the 100 million earths

Dimitar Sasselov uses a recent event in history – the reburial of Copernicus with honors in his native Poland – as a way of discussing a major discovery in his own work. Like most of his contemporaries, Copernicus had been buried in a communal grave. Scientists found hairs in a book which they knew to be in his library and attempted to match them to remains in the crypt where he was buried. By comparing DNA, they were able to make a confident match and exhume his remains, reburying them with the recognition deserving of the man who changed our understanding of the solar system to a heliocentric one.

Despite advances in DNA sequencing and other technologies, Sasselov tells us that it often seems like we’re not making much progress in answering the essential questions of life. What is life? What is the origin of life? Is there life on other planets or are we alone?

With the launch of a new telescope, the Kepler telescope, there’s a new way to look for earth-like planets in orbit around other stars. The telescope uses the transit method – it looks for the mini eclipse that occurs when a planet passes in front of a star. By detecting the dimming of the light, the users of the telescope are able to extrapolate the size and period of orbit of the planets blocking the light.

In our solar system, we have five small, earth-like planets and a smaller set (four) of differently sized gaseous planets. Copernicus believed that there was a harmony in the relationship of planet size, a distribution with more small planets like ours, and fewer large ones.

For years, it looked like Copernicus had gotten it wrong – it seemed like large, gaseous planets were more common. But this is likely just because we can only see the big ones. With Kepler now in use, this pattern is inverting – a set of 1160 observations shows far more small, earth-like planets in orbits around varying stars, and a smaller set of large gas giants – basically, a Pareto distribution with respect to planetary size.

Sasselov extrapolates from this data to suggest that there are a large number of earth-sized planets out there. Size matters, because life as we know it is more likely to occur on small planets, capable of supporting an atmosphere or liquid water. He suggests there are 100 million potentially habitable planets and that the next research project is to start studying them, trying to understand their chemical composition and, therefore, the possibility they support certain types of life.

If these experiments to enumerate planets are one form of exploring the possibility of non-terrestrial life, another major approach – which he explains as two sides of a bridge being built to join over a river – is lab experimentation. Recent experiments show that agitation of chemicals in liquid water can lead to the formation of bubble membranes that resemble cell membranes. This offers the intriguing suggestion that cell structures could be universal.

It’s easy to see ourselves as insignificantly small in the scale of the universe. Sasselov takes off his tie, asks us to imagine its length as that of the universe. Our planet is the size of an atom in this scale. But in time scales, the fraction of time our planet has been in existence is a large portion of his tie – a handful or so. Perhaps this helps us see our place in the world is not insignificant.