Did life get started in a cosmic barbecue?
Ralf Kaiser is investigating how the first chemical bonds that led to DNA may have formed close to hot, carbon-rich stars
OINTERVIEWED BY PAUL SUTHERLAND
ne of the big mysteries in nature is how life originated. We know that DNA, that famous double helix, carries the code for life. I have been part of a team working to discover how the potential precursors to the building blocks of DNA – carbon ring structures embedded with nitrogen atoms – might have formed. These are the forerunners to key components of nucleobases, critical components of DNA. We want to find out how nitrogen atoms become incorporated into these bases.
Different theories suggest that these structures can be formed on Earth under very extreme conditions, which we felt were too specific to have distributed them widely. We looked to see how they might have been formed in space. So we tried to recreate cosmic conditions in the laboratory.
For many years, astronomers have used powerful telescopes to search for signatures of nitrogen-containing hydrocarbons called quinoline, focusing mostly on the space between stars – the interstellar medium.
I’m a physical chemist and I wanted to see if these precursors to life would form in hotspots like those found close to carbon-rich, dying stars – in a kind of cosmic barbecue. Our study focused only on the formation of nitrogen-bearing bicyclic molecules. It didn’t apply to other bio-relevant molecules such as amino acids and polypeptides, for example. But it’s one specific ingredient for life, if you like, and we were looking to see how it formed.
We were doing a laboratory experiment under very well-defined conditions where we knew the reacting conditions, the product, and the reaction pathway. And our major goal was to bring this research to the next level to help understand how precursors to life can be formed in space.
We decided to look at hotspots in space, but it could be that the molecules can also form in the Prof Ralf Kaiser ponders the meaning of life at the Department of Chemistry, University of Hawaii at Manoa, Honolulu. condensed gas phase, in the icy regions found in giant molecular clouds. We haven’t investigated the cold spaces yet. Rarely have scientists looked for that on a molecular level under well-defined laboratory conditions. We also carried out simulation experiments to mimic the chemical and physical conditions that would be found near a star using a device called a ‘hot nozzle’, which had previously been used successfully to confirm soot formation during combustion. In our study the hot nozzle was used to simulate the temperatures close to carbon-rich stars. We injected a gas made of a nitrogen-containing singleringed carbon molecule and two short carbon-hydrogen molecules called acetylene into the hot nozzle, at temperatures of around 700 Kelvin, or twice the maximum heat inside a domestic oven. Then, using synchrotron radiation (radiation created by charged particles in a magnetic field), we probed the hot gas to see which molecules formed. We found that the nozzle transformed the initial gas into one made of nitrogen-containing ring molecules quinoline and isoquinoline, which are considered the next step up in terms of complexity.
It was a very successful experiment for us in identifying a precursor molecule. It suggests these molecules can be synthesised in hot environments, then be carried by stellar winds to the interstellar medium where they condense as ices on cold nanoparticles (interstellar grains). For me it is pretty fascinating to be looking at what nature started a few billion years ago. When we can put all the parts of the puzzle together in a few years time, we might have a better answer to how complex nitrogen bases can be formed in space.
We are not even close to creating life in the lab, and we don’t claim that will ever be possible. But our work may help tell us how life might have got started, and how the basic ingredients might have formed on a molecular level.