The stuff of life

Ken Tapping's weekly column on astrophysics from the Herzberg Institute

Some years ago two scientists, named Miller and Urie, put the gases that would be present in the atmosphere of a newly-born planet and passed simulated lightning through it. The result was a brown gunk at the bottom of the flask which was found to contain amino acids, the building blocks of proteins, fundamental to life as we know it. This idea caught on to the point where we more or less took it as a given that the chemistry of life started in the lightning storms of young planets. The idea was so “tidy” and “makes sense”, that we didn’t question it. Now we are finding evidence that the story is more intriguing than that experiment suggests.

Cosmic chemistry is now a major branch of astronomy. By making observations at very short wavelengths, using instruments such as the James Clerk Maxwell Telescope – in which we have a 25 per cent share – we can look at the radio signatures of molecules in the dark, cold clouds that are common in the space between the stars. It is possible to track chemical reactions and monitor what is happening inside the clouds, even though with our optical telescopes we cannot penetrate them. What we are finding is more than fascinating.

Soon after our universe began almost 14 billion years ago, and it had cooled to the point where matter as we know it could exist, hydrogen was by far the most common element; the next most common was helium, and there was not much else. You cannot do much with this chemical mix, other than make stars. However, stars obtain energy by turning small atoms, such as hydrogen, into bigger ones, such as helium, oxygen, carbon, phosphorus and so on, to atoms as heavy as iron. The stars in the young universe were large, bright and blue, and mostly ended their lives by blowing themselves up. In the explosion, heavier elements, such as gold, copper, silver and uranium were made, and the other elements formed during the life of the star were thrown out to enrich those hydrogen clouds.

In the cold, dark interiors of those clouds, screened from the harsh radiation of nearby stars, this rich mixture of elements started to react, and chemistry got to work. The biggest problem with the observations is not detecting the signatures of these cosmic molecules; it is identifying them from a dense crowd of overlapping signatures. There is water, methanol, ethanol, ammonia, formaldehyde and much, much more. Lab experiments where mixtures of cosmic chemicals were cooled to the temperature of the clouds, about -260 C, and bombarded with simulated cosmic rays, which are high-energy particles, led to the formation of aminoacids. Since cosmic rays fill space, we should expect aminoacids to form almost anywhere, such as on ice grains in comets, and on other handy bodies such as pieces of rock. This is supported by the discovery that some meteorites contain aminoacids. These results suggest carbon-based life is common in the universe, wherever conditions permit the appropriate chemistry. Of course we won’t know for sure until we find some.

Venus is disappearing into the sunset glare. Mars and Saturn dominate the southern sky. The Moon will be full on the 4th. Venus moves between us and the Sun on the 6th – the “Transit of Venus.”

Ken Tapping is an astronomer with the National Research Council’s Herzberg Institute of Astrophysics, and is based at the Dominion Radio Astrophysical Observatory, Penticton.