Why ASM?
MIT All Small Molecules project
All Small Molecules (ASM) is a library of molecules designed as a guide for research on biosignatures gases in the search for life on another planets.
In its current form the list contains ca. 16000 molecules, constructed by a combinatorial approach and an intense literature search.
Our motivation in constructing the database was to characterise what chemistry life uses that could be detectable on other worlds. However ASM could be used for any research in which possiblities need to be explored, including volcanic chemistry, industrial gas chemistry or atmospheric physics. We look forward to seeing how you, the research community, come up with uses we have never thought of.
Only a few hundred organisms have been studied for their production of volatiles compounds, out of the estimated millions inhabiting the planet. This suggests that many more chemicals remain to be discovered as gases produced by life on Earth, and that life on other worlds could produce a collection of chemicals quite different from our own biosphere.
We have classified the chemicals made by life on Earth into three types
- Type I: Byproduct from biological energy extraction from chemical potential energy gradients. Examples include methane from methanogenesis, sulfur dioxide from sulfur oxidation
- Type II: Byproduct gases from biomass building. Examples include oxygen from photosynthesis, sulfur from anoxygenic photosynthesis
- Type III: Produced for secondary or unknown reasons, such as stress or signaling. Examples include methyl chloride, carbondisulfide, isoprene
This classification is based not on what the chemcials are but on why life makes them, which helps us evaluate whether the same biological need would drive life to make different chemicals on a different world.
(see this paper for a more detailed discussion of the classification)
The ASM project aims to list all possible small molecule gases. This means that the great majority of molecules in ASM library probably belong to the Type III category. We postulate that Type III gases could be ideal biosignatures. Life on Earth makes smaller amounts of them, but they are less likely to have geological false-positives, like methane (Type I) or even oxygen (Type II).
The ASM database can be used as the basis for assesing whether a gas could, in principle, be a biosignature gas, and if so how we might detect it. We have already provided a first pass evaluation of the stability and volatility of molecules in the list of molecules of up to 6 non-hydrogen atoms. Future work will extend the list to larger molecules, more information on stability (e.g. predicted photostability, and reactivity with other atmospheric components), and add information of possible detection methods such as IR spectra.