A variable UV light source could be designed to simulate the spectrum and variability of astronomical UV radiation from stars of different characteristics, from flares, from supernovas, and so on and then used to study gene activation as a result of that radiation. Such a light source could also be used to drive directed evolution experiments in many generations exposed to this light source. Subsequent gene sequencing and structure analysis would permit study of the robustness of repair mechanisms and the possibility of novel repair pathways in extraterrestrial environments (for instance, the flare-dominated environment of a low-mass star; see the section “Cosmic, Solar, and Terrestrial Irradiation”). Coordinated experimental, theoretical, and computational work could address the interplay of astronomical and planetary environments, chemistry, mutation, diversity, fitness, and cooperation.

In addition, with the invention of alternative amino acid coding systems, there is the potential to engineer microbes based on such alternative coding systems and to study their response in directed evolution experiments that simulate astronomical bolide impact and UV or ionizing radiation environments. The point of such experiments would be not to explicitly attempt to mimic life on another planet but to use these engineered microbes to begin to explore the possible range of response and sensitivity in this extension of parameter space. The goal would be to better understand the guiding principles for the character and limits of life that evolves anywhere in a naturally fluctuating astronomical environment.

Artificial life experiments can explore a much wider range of parameter space than in vitro directed evolution experiments. Further study of simulated life promises to improve our understanding of the principles behind the growth of complexity in living systems. Experiments using neural networks as the phenotype for digital genomes are especially promising.

Astrophysicists who work on irradiation need to team with biologists who can examine the effects of these same types and levels of irradiation on molecules and cells in defined experimental systems (e.g., using directed evolution in vitro), both in solution and in the solid phase (e.g., using clay minerals as catalysts). Similar studies could be done on prebiotic chemistry.

Finding. We do not fully understand the strongly variable effects of astronomical bolide impacts or of the irradiation of the surfaces, oceans, and atmospheres of planets and moons on genetic and cellular evolution.

Recommendation. NASA, other funding agencies, and the research community should devote funding and effort to promote understanding of (1) the evolution of earthlike organisms and (2) organisms with other coding mechanisms that are subjected to the fluctuating thermal and radiation environments expected for planetary systems with various impact histories and planets orbiting stars of various masses and ages in different parts of the Galaxy.

Recommendation. NASA and other relevant agencies should foster in vitro and in silico studies to learn how the stochastic variability of the environment, including the mutational environment, affects the evolution of life, especially by promoting complexity and the evolution of evolvability.

Programs of Other Agencies

The NSF Tree of Life and DOE Genomes to Life programs will provide basic genetic information that can be used for biochemical experiments and molecular phylogenetic studies designed to learn more about the response of DNA radiation repair pathways to fluctuating thermal and radiation environments.

The NIH supports biomedical studies of the origin and treatment of cancer, genetic diseases, and aging. These studies could be significant for astrobiology because they would improve our understanding of the role of variable thermal and radiation environments in the evolution of life.

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