Possibilities for methanogenic and acetogenic life in molecular cloud

Abstract: According to panspermia, life on Earth may have originated from life forms transported through space from elsewhere. These life forms could have passed through molecular clouds, where the process of methanogenesis could have provided enough energy to sustain living organisms. In this study, we have calculated the Gibbs free energy released from synthesizing hydrocarbons for methanogenic (acetogenic) life in a molecular cloud, with methane (acetic acid) as the final metabolic product. Our calculations demonstrate that the chemical reactions during methanogenesis can release enough free energy to support living organisms. The methanogenic life may have served as the predecessor of life on Earth, and there is some preliminary evidence from various molecular biology studies to support this idea. Furthermore, we propose a potential distinguishing signal to test our model.

• The paper demonstrates that key reactions in molecular clouds can release -60 to -370 kJ/mol Gibbs free energy, potentially sustaining life.
• It employs thermodynamic calculations of reactions, comparing interstellar conditions with Earth’s subsurface methanogenesis and acetogenesis.
• The study suggests these metabolic processes may have ancient origins, offering new biosignatures for astrobiology and the panspermia hypothesis.

Methanogenic and Acetogenic Life Potential in Molecular Clouds

The paper "Possibilities for methanogenic and acetogenic life in molecular cloud" by Lei Feng presents a theoretical exploration of life forms that could potentially exist in the extreme environments of molecular clouds. Building on the panspermia hypothesis, which posits that life on Earth may have extraterrestrial origins, the study examines whether molecular clouds could sustain primitive life forms through methanogenesis and acetogenesis, with methane and acetic acid as the resultant metabolic products.

Core Concepts and Methodologies

The study hinges on a biochemical mechanism of energy acquisition similar to processes found in Earth's subsurface environments, notably methanogenesis. On Earth, methanogenic archaea perform anaerobic respiration using carbon dioxide and hydrogen, generating methane and releasing Gibbs free energy. This study investigates the viability of such processes in molecular clouds, environments rich in potential reactants like $\rm H_2$, $\rm CO$, and $\rm CO_2$.

To assess the feasibility of these life-supporting processes, the authors calculate the Gibbs free energy associated with the synthesis of methane and acetic acid under conditions typical of molecular clouds. This involves using known thermodynamic data for the reactants and products, along with estimated partial pressures of these molecules. Several potential reactions are examined, including:

1. $\rm CO_2 + 4H_2 \rightarrow CH_4 + 2H_2O$
2. $\rm 2CO_2 + 4H_2 \rightarrow CH_3COOH + 2H_2O$
3. $\rm CO + 3H_2 \rightarrow CH_4 + H_2O$
4. $\rm C_2H_2 + 3H_2 \rightarrow 2CH_4$

The calculation results revealed that these reactions could release sufficient Gibbs free energy to sustain life, ranging from approximately -60 to -370 kJ/mol.

Implications and Insights

The study suggests that methanogenic or acetogenic life forms within molecular clouds might have predated Earth's life, and potentially contributed to the ancestry of the Last Universal Common Ancestor (LUCA). This hypothesis aligns with some contemporary insights from molecular biology, which indicate methanogenesis as an ancient evolutionary trait.

From a broader perspective, the possibility of life in molecular clouds challenges our understanding of biosphere boundaries and the diverse environmental conditions under which life can thrive. If such life forms exist, they would hold significant implications for astrobiology and the search for life beyond Earth. Furthermore, the presence of methanogens or acetogens could affect the chemical profiles of interstellar environments where they reside, potentially serving as detectable biosignatures.

Prospective Research Directions

While the paper provides a robust theoretical foundation, the model and assumptions necessitate empirical validation. Future research might focus on observational campaigns aimed at detecting the proposed bio-signatures, such as specific spatial distributions of methane and acetic acid in molecular clouds correlated with carbonaceous solid deposits. Advanced telescopes and detection technologies, including space-based observatories, could play crucial roles in these endeavors. Moreover, laboratory simulations of molecular cloud conditions could refine our understanding of potential metabolic pathways in extreme extraterrestrial environments.

In conclusion, this research opens intriguing lines of inquiry into the possibilities for life in the cosmos, urging a reevaluation of life's adaptability and its potential cosmic ubiquity.