Interstellar ice may hold the secret to life

Trying to understand the origins of life is perhaps the most difficult problem for chemists and biologists.  The complex molecules which make up life, such as DNA and proteins, are built from smaller organic molecules, which some scientists believe originated in space. Building blocks for life, including simple sugars, amino acids and components of RNA have all been detected in comets and asteroids, although it is unclear how these molecules form.

Now, a team of physicists from the University of Sherbrooke in Quebec, Canada, have generated key organic molecules in conditions that simulate deep space, bombarding frozen films of methane and oxygen with electrons. These icy films simulate the conditions of interstellar dust clouds, comets and other stellar objects, where simple molecules such as methane condense around dust particles.

Previous studies have looked at the effects of high energy radiation on these frozen films, but Sasan Esmaili, the lead author in this work, believed that interstellar chemistry may be driven by low energy electrons, rather than X-rays, gamma rays or high energy particles.

When high energy radiation interacts with matter, a burst of lower energy electrons can be produced. Esmaili’s hypothesis was that these electrons, rather than the high energy radiation, could be responsible for much of the chemistry that produces organic molecules in space. 

Esmaili’s team worked under ultra-high vacuum, at temperatures of 22 degrees Kelvin (-251 Celsius) to condense methane and oxygen onto a platinum surface.  They then irradiated the films with an electron beam with an energy of 70 electron-Volts to simulate the effects of electrons generated in space from high energy radiation colliding with matter.

The frozen films were analysed by a number of powerful techniques, including Electron Stimulated Desorbtion (ESD) mass spectrometry, to identify the new molecules that had formed. Frozen films of methane were found to produce small hydrocarbons such a propylene, ethane and acetylene.  When a methane-oxygen mixture was subjected to the electron beam, the formation of ethanol was observed, along with evidence for the formation of methanol and acetic acid.

These small organic molecules could all be precursors to more complex molecules, especially when other important elements like nitrogen are introduced. The work offers a possible new explanation for how the critical building blocks of life may have originated, from a burst of electrons generated by interstellar radiation. 

Esmaili and colleagues conclude: “This radiation-driven molecular synthesis may indeed represent a driving force in the original biogenesis of the molecular building blocks of life in our own solar system and, due to the ubiquitous nature of matter and radiation, may represent a key element in molecular biogenesis throughout the universe.”

The research is published in The Journal of Chemical Physics.