Goal 7
Explore the physical and chemical limits
to which life adapts as a guide for searching for life on other worlds.
Characterize the biota that live under conditions relevant to the search for life elsewhere in the Solar System. Characterize the fundamental molecular adaptations that allow biota to thrive or at least survive under these conditions.
Life is found surviving and in some cases even thriving under some of the harshest conditions on Earth (e.g., geothermal hot springs, acidic drainage, deserts, permafrost, the high-pressures of the deep sea, and the artificial radiation fields of nuclear reactors). Ongoing exploration of such environments continues to lead to the discovery, isolation, and characterization of life forms that are either surviving or actively growing under what appear to be biochemically challenging conditions. The existence of living organisms under such extreme conditions raises fundamental questions about the physical and chemical limits for life and about the biochemical adaptations that set those limits. What are the environmental conditions that define the limits for life as we know it? How have all the critical constituents of living systems been adapted to survive or function under these harsh conditions? And most importantly, how does this guide the quest in astrobiology to find life in other worlds?
An understanding of the tenacity and versatility of life on Earth, as well as an understanding of the molecular defenses and repair systems that these organisms use to survive such extremes, will provide a critical foundation for the search for life beyond Earth. Insights into survival strategies that are effective on time-scales relevant to space travel will provide a basis for evaluating theories of ‘panspermia'. These insights will help us to understand the molecular adaptations that define the physical and chemical limits for life on Earth, and they will provide a baseline for developing predictions and hypotheses about life on other worlds.
- Objective 7.1—Explore
for life that survives or thrives under the most extreme conditions
on Earth. Examine the combined impact
of factors such as high temperature and low pH, or ionizing radiation
and low nutrients, or extreme cold and desiccation and high salt, and
most importantly, the impact of duration of exposure to any condition.
These all contribute to defining limits for life that are relevant to
astrobiology.
- Objective 7.2—Characterize
and elucidate the biochemical adaptations that define the limits for
the individual, the species, and for life itself. Investigate
the intrinsic stabilities of biomolecules (e.g., proteins, nucleic acids,
lipids, carbohydrates), both in isolation and in the complexity of living
cells, to understand the limit for living systems. Explore the biochemical
strategies that cells have evolved in order to push the limits by reinforcing,
replacing, or repairing critical biomolecules (e.g., spore formation,
resting stages, membrane stabilization, protein replacement rates, or
DNA repair).
- Objective 7.3—Adaptation of life beyond Earth. Explore the adaptation, survival and evolution of life under novel environmental conditions, particularly space and other planets.