Chemical Pathways to Life: Amino Acids and their Precursors in the ISM

The long-standing question about the emergence of life on Earth has attracted great interest among researchers and the general public for decades. One of the proposed scenarios involves the delivery of biologically important compounds such as amino acids on the primordial Earth by the impact of meteorites on the Earth's surface. In the early 90's, several works reported the discovery of more than seventy amino acids in meteorites, the majority of which have no known terrestrial occurrence. This finding supports the exogenous hypothesis for the origin of life.

It is thus currently believed that amino acids may have formed in the interstellar medium, where complex organics, i.e. large carbon-based molecules, have been found. Laboratory experiments of highly energetic processes such as illumination by ultraviolet photons or bombardment by cosmic rays on interstellar ice analogs, have indeed found that these processes are very efficient in the production of large organic molecules and, in particular, in the formation of amino acids.

Despite this progress in the past twenty years, the direct detection of amino acids in the interstellar medium remains elusive. Previous works focused on the search of amino acids in regions across the Galaxy where massive stars form. These regions are relatively hot, and are known to show an active chemistry which induces the production of large amounts of complex organics. The spectrum of light observed toward these regions is highly populated by molecular emission lines at millimeter and sub-millimeter wavelengths, resembling a forest of lines. In this highly populated spectra, the brightest line features correspond to the more abundant species in the interstellar medium. This makes the identification of less abundant species such as amino acids challenging. As a consequence, no firm detection of amino acids in the interstellar medium has been reported to date.

In this research project, we will use a novel theoretical and observational approach to detect the simplest amino acids, glycine and alanine, in the interstellar medium. This approach considers that the initial stages in the formation of Solar-type systems, characterized by very cold temperatures (about 10 degrees above absolute zero), are better suited for the detection of amino acids.

In a first step, the chemistry of glycine and alanine will be characterized theoretically assuming very cold conditions resembling those of young Solar-type systems. This will help us to infer the main chemical routes involved in the destruction and formation of glycine and alanine at cold temperatures. In a second step, we will perform theoretical modelling of the emission spectrum of these species. This will allow us to establish the parts of the spectrum of light where the probability to detect glycine and alanine is higher. Finally, we will perform deep observations of these species by using the unprecedented capabilities of the Atacama Large Millimeter/Sub-millimeter Array (ALMA) located on the Chajnantor plateau in Chile. The increased sensitivity of this facility (by more than a factor of 10 with respect to previous instrumentation) offers the opportunity, for the first time, to accomplish the detection of amino acids in space.

This research not only will allow us to fully characterize the pre-biotic chemistry of amino acids, but will allow us to directly link the formation of these complex organics in the interstellar medium with their subsequent delivery onto planetary systems. The detection of amino acids at the early stages in the formation of Solar-type systems will represent a milestone in our understanding of the emergence of life on Earth.

The results derived from this research are expected to have a high impact on the wider public because of their immediate implications on how key biological ingredients for life such as amino acids may have originated in the Universe. This topic attracts large interest from all audiences and its relevance has been recognized by the STFC as indicated in its Strategy Report, "A new vision for new times" (http://www.stfc.ac.uk/resources/pdf/vision.pdf).

The question about the origin of life requires answers to a wide variety of second level unknowns. And by the end of this research grant we will be in a strong position to answer whether the simplest amino acids, glycine and alanine, could have formed in very cold gas at the earliest stages in the formation of Solar-type systems. This will provide a natural way to explain how these biologically important compounds may have reached the surface of the primordial Earth by meteorite impacts, and it will help us to understand whether these processes occur in other Solar-type systems across the Galaxy.

Because of their high impact, these results have the potential to inspire and encourage young people to pursue research careers in Astronomy and Astrochemistry. This is strategically important for the UK since young students will be the future users of cutting edge facilities such as the Atacama Large Millimeter/Sub-millimeter Array (ALMA) and the Square Kilometer Array (SKA). This will secure continuity for these facilities as well as momentum to design future radio and millimeter/sub-millimeter instrumentation, with its subsequent impact on the industry and economy sectors in the UK.