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Fundamental Questions, Specific Science Goals, and Measurement Objectives in Astrobiology
Draft--July 7, 1998
Contents
Question 1: How do habitable worlds form and how do they evolve?
Question 2: How Did Living Systems Emerge?
Question 3: How can other biospheres be recognized?
Question 4: How have the Earth and its biosphere influenced each other over time?
Question 5: How do rapid rates of environmental change affect emergent ecosystem properties?
Question 6: What is the potential for survival and adaptation beyond the home planet?
Question 1: How do habitable worlds form and how do they evolve?
Goal 1.1: Determine how stars and planetary systems form and understand what parameters determine the properties of the resulting systems.
The Kant-Laplace hypothesis of the coupled formation of stars and planetary systems has been spectacularly verified by a wealth of observations in the last few decades. Observations of star-forming regions have been able to identify examples of nearly every stage in the star formation process: precollapse dense molecular cloud cores, young protostars surrounded by infalling molecular cloud gas and dust, and pre-main-sequence stars newly emerged from their placental cloud cores. Both protostars and pre-main-sequence stars exhibit a variety of evidence for the presence of the protoplanetary disks long predicted by theory to be the sites of planet formation. While protoplanets have not yet been detected within these disks, the discovery of a number of likely gas giant planets in orbit around nearby solar-type stars provides much-needed information about the outcome of the planet-formation process around stars other than our sun. In order to understand fully the process of planet formation, these observations of specific phases must be linked together into a cohesive, chronological scenario. This linkage must rely largely on theoretical modeling, and on laboratory studies of otherwise unobservable phases, e.g., the cloud collapse phase prior to the appearance of young stellar objects, or the growth of dust grains from sub-micron size to kilometer-size, self-gravitating planetesimals. In addition, telescopic observations at a variety of wavelengths and laboratory studies of extraterrestrial materials are needed to achieve a complete understanding.
Objective 1.1.1: Determine whether a dense cloud core forms a single star like the Sun or a multiple star system.
[Required: observations of precollapse clouds and binary protostars, theory of collapse, fragmentation, and orbital evolution of fragments, laboratory studies of molecular cloud coolants and chemical tracers]
Objective 1.1.2: Determine the physical and chemical characteristics of suspected planet-forming disks and how they evolve.
[Required: observations of circumstellar disks at high spatial and spectral resolution at long wavelengths, theory of cloud collapse to form disks and of disk evolution mechanisms, laboratory studies of dust grain growth and chemical evolution, of meteorites, interplanetary dust particles, and other extraterrestrial materials]
Objective 1.1.3: Understand the ultimate outcome of the planet formation process around other stars--i.e the structure and mass distribution of the resulting planetary system.
[Required: observations of protoplanets in the process of formation as well as a census of mature planets around nearby main-sequence stars, theory of planetary accumulation and formation processes, laboratory studies of volatile evolution during collisional accumulation]
Objective 1.1.4: Determine the chemical composition of the gas, ice particles, dust, and smaller bodies (comets, meteorites) which add to the chemical inventory of the planets and satellites in the habitable zone.
[Required: observations of precollapse clouds and circumstellar disks at high spatial and spectral (IR-radio) resolution; further development of cloud collapse and planet formation theoretical models including detailed chemical processes; laboratory studies of gas, ice, and dust analogs which include realistic energetic processing simulations to accumulate appropriate spectral and physical/chemical properties; laboratory studies of those materials shown to be important, carried out under realistic primitive conditions, to test the endogenic and exogenic origin of life hypotheses]
Goal 1.2: Understand what properties characterize a habitable world and what the chances are that other habitable worlds exist.
Habitability depends crucially on the narrowness of the definition of life. If we are referring to carbon-based, organic molecules, then the issue of habitability is that of sustaining a chemical medium in which nutrient and waste transport can occur under controllable conditions, catalytic function is possible, and genetic code can be protected, reproduced, and moved within the life form to sites of production of structural and functional molecules. The medium must be stable over long periods of time so as to allow for life forms to be sustained and perhaps evolve if we want to see anything interesting. There must be a source of energy which maintains the system away from the equilibrium state, i.e., provides a reservoir of free energy in the thermodynamical sense.
Under these requirements a habitable world is one with a liquid medium playing host to organic processes, and water seems the most versatile candidate, though ammonia-water or liquid hydrocarbons salted with polar molecules are also possible choices. The medium must be sustained in a temperature range which allows both the liquid state and organic bonding to exist. Thus we look for planets with accessible liquid media, long-term climate controls (long enough for life to develop and hence be detected), and energy sources/sites that pull organic systems well away from thermodynamic equilibrium.
Although it is important to pursue the general question of habitability, it is important to note that all life with which we are familiar here on Earth requires liquid water during at least some stage of its life cycle. Therefore, from a practical standpoint, the search for life off the Earth should begin with the search for liquid water. Even with this limitation, there are many questions to be answered in order to understand where life might exist. Where did Earth's water come from in the first place? Was it included in the original planetesimals from which Earth formed, or was most of it added later by impacts of asteroids or comets? And what caused it to stay liquid throughout most of Earth's history? The Sun has increased in brightness by about 40% during this time, yet the geologic evidence for liquid water and for life goes back at least 4 billion years. What greenhouse gases kept Earth warm during its early history, and would the same gases be present on other planets besides Earth?
A related question concerns the width of the habitable zone around the Sun and other stars. The habitable zone, or HZ, is defined as the region where liquid water is stable on a planet's surface. One-dimensional climate model calculations predict that the current HZ around our own Sun extends from about 0.95 AU out to ~1.5 AU, but these calculations do not include the effect of clouds on planetary climates. Water clouds are expected to become abundant near the inner edge of the HZ, whereas CO2 clouds may form near the outer edge. Three-dimensional climate modeling is needed to determine where the habitability limits actually lie. Finally, liquid water may be present in subsurface environments on planets or moons outside of the HZ. Mars, for example, may have a liquid aquifer several kilometers beneath its surface, and Jupiter's moon, Europa, is thought to have water beneath its icy surface. Could life exist in these environments? Such questions cannot be answered by modeling, but they may eventually be answered by direct investigation.
Objective 1.2.1: Find the origin of Earth's volatile, life-supporting elements (C, H, O, N, S, and P). (Discuss sources of volatiles; e.g., comets, asteroids, etc.)
Objective 1.2.2: Discover the sites where liquid water exists in our own solar system. (Earth, Mars subsurface, Europa)
Objective 1.2.3: Understand why Earth remained habitable despite large predicted changes in solar luminosity during its history. (CO2 variations, other greenhouse gases)
Objective 1.2.4: Understand what determines the width of the habitable zone around the Sun and other stars, and explore the possible distributions. (Discuss effects of clouds, need for 3-D climate modeling.)
Objective 1.2.5: Explore the range of conditions (i.e. star systems different from the Sun) under which habitable planets can exist. (Tidal locking problem around M stars, UV problem around early-type stars, habitable planets around binary stars)
Goal 1.3: Understand how habitable worlds change once they become inhabited.
The surface environment of a planet determines whether life can exist there or not. But life, once it has originated, can also influence the surface environment of the planet. It does so by altering the abundance of greenhouse gases, such as carbon dioxide and methane, and by causing changes in the oxygen abundance in the planet's atmosphere. Thus, to understand how an inhabited planet evolves, we need to study the co-evolution of the planet and its biota.
To begin this study, we need to better understand what Earth's atmosphere was like prior to the origin of life. Were the volcanic gases given off at that time similar to those emitted today, or was the primitive mantle more reduced? How fast did hydrogen escape from the atmosphere and what was the H2 partial pressure? Was methane a significant component of the atmospheric greenhouse?
We then need to consider how the environment may have been modified by the presence of life. Molecular phylogeny suggests that methanogenic bacteria may have been some of the earliest types of organisms to evolve. These bacteria would have used CO2 and H2 from the atmosphere to produce CH4. The CH4 given off should have contributed to the atmospheric greenhouse effect and might also have been photolyzed to produce hydrocarbon haze similar to that observed on Saturn's moon, Titan. This haze, if present, would have affected climate directly by absorbing incoming solar radiation, and it may also have shielded the surface from solar UV radiation. Most of this methane would have disappeared, however, once photosynthetic O2 began to accumulate in the atmosphere. The rise of O2 would have caused a corresponding rise in ozone, and the combination of higher O2 levels and better UV shielding made possible the development of more advanced organisms -- the eukaryotes (organisms with nucleated cells). The eukaryotes, which include all multicellular forms of life, should in turn have caused further rises in atmospheric O2 by providing more efficient pathways for photosynthesis and organic carbon burial. Understanding how Earth's biota and surface environment co-evolved may help us to predict whether similar things should be expected on inhabited planets around other stars.
Objective 1.3.1: Determine the state of the primitive mantle, with respect to reduction, and what dominant volcanic gases were released from it. (Discuss problem of core formation, excess siderophiles, mantle redox evolution)
Objective 1.3.2: Understand how primitive, non-photosynthetic life would have affected the composition of Earth's atmosphere. (Discuss methanogenic bacteria, other bacteria)
Objective 1.3.3: Determine if reduced greenhouse gases such as methane and ammonia contributed significantly to the greenhouse effect on early Earth. (Discuss organic haze formation, UV shielding)
Objective 1.3.4: Enumerate the mechanisms that controlled the hydrogen escape rate from Earth, and determine how hydrogen escape would have affected the concentrations of reduced greenhouse gases in Earth's primitive atmosphere. (Discuss diffusion-limited flux, hydrodynamic escape, energy-limited escape)
Objective 1.3.5: Find out when O2 first rise to appreciable levels in Earth's atmosphere, and what determined the rise. (Discuss geological evidence, theories of why O2 rose)
Objective 1.3.6: Determine when a biologically-effective UV screen was first established. (Discuss time history of atmospheric O2, photochemical modeling of ozone abundances.)
Goal 1.4: Determine the observable characteristics of habitable or inhabited worlds that can be detected using either remote and in situ techniques.
A major goal of NASA's Origins program is to identify potential sites of life, or even life itself, elsewhere in the solar system and elsewhere in the cosmos. This goal requires that we carbon-based organisms develop a working definition of what we mean by "life" and what that understanding implies for the biological prerequisites for life. In identifying what we mean by life and its acceptable environs we must maintain as broad an outlook as possible, while still discriminating likely habitats from unlikely ones.
One can divide this goal into four distinct subgoals: using either remote sensing or in situ techniques to identify habitable venues and to find evidence for life itself (either extant or extinct).
Objective 1.4.1: Search in situ for stable reservoirs of liquid water or for geological evidence of water.
Objective 1.4.2: Search in situ for chemical and isotopic signatures of life in gaseous or aqueous environments.
Objective 1.4.3: Look in situ for slugs and bugs (fossil or extant life).
Objective 1.4.4: Using remote sensing techniques, look for an atmosphere and analyze its composition.
Objective 1.4.5: Using remote sensing techniques, look for chemical/isotopic signatures of life
Objective 1.4.6: Using remote sensing, look for signs of intelligent life
Question 2: How Did Living Systems Emerge?
The origin and evolution of life are inextricably intertwined with those of the host planet. As a planet’s environment changes over time, so will its potential for spawning and sustaining life. Moreover, planets with similar histories and biological potential early on may take divergent evolutionary tracks due to differences in intrinsic properties, and life may retreat to limited oases or become extinct in one but not in another. Understanding how life originated on Earth provides a paradigm whose applicability elsewhere in the solar system and cosmos can be tested. Is life on Earth unique? How does the history of life on Earth inform us about the prospects for life on Mars or elsewhere in the solar system or beyond? Much of today’s knowledge of early Earth, however, was either unknown when a modern theory of the origin of life was first proposed or contradicts what was then known. Insofar as life is indeed a planetary phenomenon, a theory of its origin must evolve to keep pace with gains in knowledge of the earliest history of the planet and its biosphere.
Recent studies have shown that the range of conditions under which microbial life forms can not only exist, but flourish, is wider than previously thought. All that life seems to need is liquid water, biogenic elements and chemical energy sources, and these may be present on other bodies in the solar system. Just as evidence of earliest life on Earth has been sought backwards in time in older and older rocks, the search for life elsewhere in our solar system should extend outward in space to Mars, Europa and other planets where habitable environments may have existed. With the discovery of planets around other stars comes the exciting prospect that extrasolar life may exist and even be detectable. The antiquity and robust character of life on Earth provides a stronger foundation than ever before for seeking signs of life on planets that are discovered orbiting stars other than the Sun. In order to interpret the remote sensing, spectroscopic data that we might obtain once such planets are discovered, we will need to understand the many ways in which life on a planet can alter the nature of that planet’s atmosphere.
Goal 2.1: Develop a theory for the origin of life from knowledge of life on Earth.
Recent evidence indicates that life began on the Earth at least 3.85 billion years ago, soon after the violent period of planetary accretion. What were the first microorganisms and their habitats like, and how did they arise from the prebiotic environment? Some insight into the answers to these questions will come from a reconstruction of the first billion years of Earth history. Progress toward that Objective has already been made during the past 30 years, and new knowledge can be gained on several fronts. Contributions will come from advances in theoretical modeling of how Earth’s surface environment changed over time. These advances coupled with an environmental history derived from investigations of the earliest geological record will provide a self consistent model of the planet over this seminal epoch in its history. It is within this environmental context that pathways for the prebiotic synthesis of biomolecules and their assembly into living systems can be formulated and assessed most fruitfully. Together, studies of the paleontology and phylogeny of Earth’s earliest biosphere can provide new knowledge of the timing and sequence of evolutionary milestones in biology. In turn, this chronology holds promise of opening a perspective backward in time on the nature of Earth’s earliest organisms and their habitats.
Objective 2.1.1: Reconstruct first billion years of Earth’s environmental history when life first arose
Objective 2.1.2: Determine the contribution of extraterrestrial organic matter to the inventory of prebiotic compounds on Earth and to the origin of life
Objective 2.1.3: Characterize the astrophysical constraints on the origin and early evolution of life on Earth, including cometary and asteroidal impacts and solar evolution among others.
Objective 2.1.4: Develop and test plausible pathways by which the ancient counterparts of membrane systems, proteins and nucleic acids formed from simpler precursors and assembled into protocells and eventually ecosystems
Objective 2.1.5: Establish the generality of physical-chemical principles which drive the emergence and earliest evolution of catalysis and self-replication as protobiological functions.
Objective 2.1.6: Discover the principles that govern cellular organization and regulation in prokaryotes
Objective 2.1.7: Characterize the traits of the universal common ancestor and the evolution of metabolism through phylogenetic and physiological studies of contemporary organisms
Objective 2.1.8: Develop models for Earth’s earliest ecosystems.
Goal 2.2: Determine whether life arose elsewhere in the solar system and beyond and whether it exists there at the present time.
Microbial life forms on Earth are found in acid-rich hot springs, alkali-rich soda lakes and saturated salt beds. Additionally, microbial life has been found in the Antarctic living in rocks and at the bottoms of perennially ice-covered lakes. It is found in deep sea hydrothermal systems at temperatures of up to 115o C. Recently, bacteria have been discovered in deep (1 km) subsurface ecosystems deriving energy from basalt weathering. Some microorganisms survive UV radiation, while others tolerate extreme starvation, low nutrient levels and low water activity. Surprisingly, spore forming bacteria are reported to have been revived from the stomachs of wasps entombed in amber dated at 25-40 million years old. Clearly life is remarkable diverse, tenacious and adaptable to extreme environments.
Some of these environments are similar to past or even present environments possibly on other planets in the solar system. There were probably hydrothermal systems and ice-covered lakes on Mars in the past as well as subsurface aquifers there today. Studies of the icy satellites Europa and Callisto by the ongoing Galileo mission have provided tantalizing, but unproven evidence of substantial liquid water oceans beneath their surfaces. The existence of life on other planets in the solar system remains an open question waiting to be addressed by further exploration. These prospects are dramatically highlighted by the recent report of evidence for life in Martian meteorite ALH84001.
Before there was life, however, there was prebiotic evolution. To fully understand the extent to which prebiotic evolution occurred in the solar system requires a knowledge of where organic chemistry occurred or is occurring and what factors in those environments either fostered or constrained the emergence of living systems.
Objective 2.2.1: Establish limits on the environmental conditions for survival and evolution of terrestrial life forms
Objective 2.1.2: Discover the molecular basis for the adaptation and survival of the structures and functions of microorganisms in extreme environments.
Objective 2.2.3: Develop a comprehensive set of criteria to distinguish between materials of biological and non-biological origins.
Objective 2.2.4: Determine the existence, morphology, biochemical characteristics and phylogeny of "nanobacteria" in extant microbial ecosystems.
Objective 2.2.5: Determine the prebiological history and biological potential of Mars and other bodies in the Solar System
Objective 2.2.6: Determine whether a liquid water ocean exists today on Europa and Callisto and seek evidence of organic chemical or biological processes
Objective 2.2.7: Characterize the range of atmospheric compositions that might be produced by an anaerobic biosphere
Objective 2.2.8: Develop theoretical models for the compositional evolution of early Earth’s atmosphere from initially anoxic to the accumulation of significant O2
Objective 2.2.9: Survey the solar neighborhood for planets with atmospheres that might either support life or indicate the presence of life
Question 3: How can other biospheres be recognized?
There are two indications that planetary systems are common around other stars. First the presence of disks (infrared spectral excesses) indicates that the nebula such as that from which the planets of our solar system are thought to have formed are found around many stars. Second the indirect detection of a number of extrasolar giant planets and the direct imaging of one further suggests that planets are common. While detection of Earth-sized planets is still beyond the current techniques employed, theories of planet formation suggest that such worlds will be detected once the appropriate methods and technologies are deployed. It is interesting therefore to consider how the presence of life could be confirmed remotely on such a world.
On the Earth life has produced easily detectable changes in the atmosphere and surface mostly as a result of plants. These include the high concentration of O2 and O3 in the atmosphere and the presence of a distinctive color feature (due to Chlorophyll) on the surface. However these effects have been most pronounced only for the last billion or so years of Earth history. For the previous several billion years during which Earth had life the atmospheric and surface signatures are not fully understood. How these processes can be generalized to other worlds orbiting other stars is a key question for Astrobiology. To address this we suggest the following goals and Objectives:
Goal 3.1. What are the atmospheric signatures of life?
Objective 3.1.1: Determine to what extent the presence of oxygen and ozone in a planetary atmosphere is indicative of life.
Objective 3.1.2: Determine the physical and biological processes of gas exchange between the biota and the atmosphere for both an anaerobic and an aerobic world including the following gases: H2, H2S, CH4, NH3, N2O, N2.
Objective 3.1.3: Determine the technological approaches that will allow identification of biogenic gases in extrasolar planetary atmospheres.
Goal 3.2. Can the presence of surface liquid water be determined remotely?
Objective 3.2.1: Can the surface temperature of a planet be determine by remote sensing across interstellar distances?
Objective 3.2.2: Can the amount of water in the troposphere of a Earth-like planet be determined remotely?
Goal 3.3. Are there surface signatures of life?
Objective 3.3.1: Does the process of photosynthesis necessarily imply a spectral signature that can be recognized as such? Can earth plants be recognized from interstellar distances in this way?
Objective 3.3.2: Do biotic processes produce mineral signatures that can be remotely detected?
Question 4: How have the Earth and its biosphere influenced each other over time?
The history of life on Earth is a rich tapestry of adaptation and innovation which has been shaped, at least in part, by the changing surface environment. To the extent that all rocky planets have followed similar evolutionary paths, studies of our own biosphere can guide our search for extraterrestrial life.
Goal 4.1: Through studies of the rock record, understand the nature and timing of early biological evolution in the context of ancient habitable environments.
The concept that the evolution of the biosphere and its environment are inextricably related should be investigated in detail. Studies of the fossil remains of ancient ecosystems could explore the relationship between the diversity of the microbiota and their microenvironments and how these changed over time. Thus it is important to understand the nature, timing, and causes of long-term changes in the global environment. For example, the increase in solar luminosity, the declining rates of meteorite impacts, the exchange of volatile materials between Earth's mantle and its crustal reservoirs, and the stabilization of continents have all shaped and changed the surface environment and the biosphere. In turn, biota have also modified their environment. They have altered rates of erosion and sedimentation and contributed to the atmosphere's inventory of reactive gases.
Objective 4.1.1: Describe the role played by both geological and cosmic processes in shaping the nature and distribution of ancient habitable environments.
Objective 4.1.2: Describe the evolution of the chemical composition, including redox state, of sea water and the atmosphere during the past 3.8 Ga.
Objective 4.1.3: Search for and describe relationships between major environmental changes and evolutionary changes in the biosphere
Objective 4.1.4: Develop the systematics for interpreting more effectively the multiple types of fossil information (morphological, chemical, isotopic, mineralogical components)
Objective 4.1.5: Develop and adapt new technologies for analyzing fossil information in the rock record
Objective 4.1.6: Characterize and quantify the processes that drive the biogeochemical cycles of the biogenic elements and describe how they might have changed over geologic time
Objective 4.1.7: Develop a model for the evolution of atmospheric composition that will serve as a guide for the search for life on extrasolar planets
Objective 4.1.8: Build effective bridges between the living biological and the geological records of the early biosphere
Goal 4.2. Understand how the structure and function of extant microorganisms and their ecosystems have recorded both the history of their evolution and their interaction with the environment.
Powerful new techniques in molecular biology are ushering in a period of revolutionary change in evolutionary studies. Molecular fingerprinting is putting names and faces on the diverse array of microorganisms, thus allowing microbial communities to be examined in ways analogous to those long-since developed for animals and plants. Analyses of molecular diversity and genetic relationships are identifying key processes that have been the very drivers of evolutionary processes. We have found that defining the functions and phylogenies of key individual polynucleotides, proteins and genes is every bit as crucial as tracing the lineages of entire organisms, if not more so. A whole new discipline of examining entire genomes is emerging, and, with it, the discovery of new principles for the understanding the structure and dynamics of biological information and its evolution. Indeed, the flood of new biological information has challenged our ability to organize and interpret it, and therefore to synthesize a more enlightened view of how biological evolution really works.
Objective 4.2.1: Improve the methods for the construction of phylogenetic trees
Objective 4.2.2: Correlate molecular phylogenies with biomarker compounds and the geologic fossil record
Objective 4.2.3: Define the molecular mechanisms involved in creating biochemical innovations (e.g., gene duplications, domain shuffling, horizontal gene transfers, other vectors of genetic information)
Objective 4.2.4: Define the total inventory of genes centrally important for microbial function and diversity
Objective 4.2.5: Define the roles of cooperation and competition in evolution at the molecular, cellular and ecosystem levels
Objective 4.2.6: Determine the phylogenies of key enzymes, for example, those involved in carbon fixation and energy transduction
Objective 4.2.7: Explore the diversity of deeply divergent unicellular eukaryotes
Objective 4.2.8: Elucidate how ecological processes extend the environmental limits of life
Objective 4.2.9: Initiate a program to acquire total genome sequences of key microbial taxa
Question 5: How do rapid rates of environmental change affect emergent ecosystem properties?
Goal 5.1: Determine how rapid rates of environmental change affect emergent ecosystem properties with implications for co-evolution of the Earth and its biosphere.
Astrobiology seeks to understand and to predict how natural and human induced changes on Earth have and will alter the adaptation and evolution of our biosphere on time scales measured in units of 10,000 years to less than one year. At the time scale of 10,000 years, the most important change has been in climate and ocean circulation from glacial maxima to interglacial periods. Changes of significance on 1,000 year time scales involve soil formation and geomorphology with implications for hydrologic and nutrient supply. At less than a year to ten year time scales, El Niño weather events, volcanic eruptions, meteorite impacts, wildfires, deforestation and desertification, exotic species invasion, decline in ozone in the stratosphere, change in atmospheric CO2, and sea level rise can all play a role in defining rapid rates of change.
Objective 5.1.1: Define the attributes of historical (e.g., pre-industrial) ecological communities that are primarily responsible for sustaining natural ecosystem structure and function during periods of rapid environmental change; e.g.,
Fire resistance and recovery
Resistance to toxicity, temperature, and inundation
UV-B protection
Drought and desiccation tolerance
Dispersal and colonization capacity
Species diversity
Objective 5.1.2: Determine the critical biophysical and geochemical components and process interactions necessary to restore an impoverished ecosystem to (a) a more historically functional stage or (b) a new evolutionary state; e.g.,
History, intensity, and spatial pattern of disturbance
Seed bank and propagule quality
Niche space and mutation patterns
Water quality and quantity
Nutrient availability
Substrate toxicity
Atmospheric chemistry and radiation
Objective 5.1.3: Determine the management functions necessary to sustain ecosystem structure and function now and during periods of future environmental change, including potential spread of life beyond the planet of origin; e.g.,
Fire impacts and management
Reduction of fragmentation and erosion
Mitigation of drought stress
Response to altered atmospheric chemistry
Species conservation
Variables to be measured (E.g., including remote sensing)
Species distribution and habitat patterns -- high spatial resolution
Biogeochemical variables (vegetation and soils) -- high spectral resolution
Hydrologic variables -- high temporal resolution
Fire properties -- thermal IR resolution
Specific Project Study Opportunities
UV increase and ozone depletion
Glacial/interglacial CO2, precipitation, temperature
Massive conflagration impacts
Regional sterilizing events
Habitat fragmentation responses and remedies
Missions and Technologies
Meteorite impact survey
'Constellation' of satellite sensors
Question 6: What is the potential for survival and adaptation beyond the home planet?
This Astrobiology question is unique and is key to Astrobiology as it establishes research requiring the integration of earth, space, life, and social sciences to understand and direct the future of life beyond Earth based on data gathered in the present and past. The approach is truly interdisciplinary. While organisms and organic precursors of life have left the surface of our planet, either intentionally through the space programs or through natural processes such as meteoritic transport, this question proposes that for the first time in human history, organisms may intentionally be "seeded" beyond Earth. A logical, scientific program with guidelines and protocols that integrates existing knowledge from space, earth, and life sciences, as well as ethical guidelines for moving beyond Earth, must be established. In addition, this question will seek to identify natural processes that already may have spread life throughout the universe in the past, now, and into the future.
Planned NASA missions will look for existent life and/or sample other planets and moons in an attempt to identify past or present life forms in our solar system. Simple organisms, especially members of Bacteria and Archaea, have been shown to survive under the conditions encountered in space and on the moon. Humans can survive and adapt beyond Earth only if an Earth-like environment is provided. Space Station will house several complex organisms in space and will allow studies across multiple generation that should determine if selected species can adapt and replicate beyond Earth. Data from these missions can provide information useful in determining the potential for the long-term survival of terrestrial life beyond the Earth. Ultimately, we must achieve a comprehensive understanding of those environmental parameters and biological processes that combine to allow life to survive, adapt, and reproduce in unique environments both on and beyond Earth.
Goal 6.1: Identify any natural processes which may spread life from one planet to another.
Objective 6.1.1: Determine the mechanisms of meteorite impact and ejection on planetary surfaces.
Objective 6.1.2: Determine the dynamical lifetimes for interplanetary and interstellar transfer.
Objective 6.1.3: Determine survival time of microorganisms on and within meteorites in the space environment.
Objective 6.1.4: Determine the ability of an incoming meteorite to inoculate a habitable planet.
Objective 6.1.5: Determine if a meteoritic, biogenetic, or metabolic record exists which indicates that life came to Earth from beyond.
Objective 6.1.6: Determine the minimum number of species, trophic levels and food chains links that must be included for providing a functional ecosystem beyond Earth. The more of these levels and links, the more diverse/complex an ecosystem. A functional ecosystem can harvest energy, incorporate it into biomass, and recycle waste. Nonfunctional ecosystems do not have these processes, especially the last process, recycling.
Objective 6.1.7: Determine the trace elements that must be present in an ecosystem in order for dietary requirements to be met.
Objective 6.1.8: Define the minimal number and level of physical environmental parameters required for organism/ecosystem survival and adaptation beyond Earth.
Objective 6.1.9: Understand the role of gravity in life and ecosystem stability.
Goal 6.2: Define the minimal ecosystem that is required for organisms to survive and then adapt beyond Earth (requires input from question: How have the Earth and its biosphere influenced each other over time?).
Objective 6.2.1: Determine the minimal gravity level required for organism/ecosystem survival and adaptability, e.g. importance of sedimentation, stratification, and convection on ecosystem diversity and distribution.
Objective 6.2.2: Define those gravity-sensitive structures that evolved to support subcellular organelles, cells, tissues, and organisms and determine the ability of such structure to adapt to gravity levels other than 1G.
Objective 6.2.3: Identify those organisms/ecosystems that can survive and adapt when exposed to the radiation species and levels that will be encountered beyond Earth.
Objective 6.2.4: Determine the molecular mechanisms associated with radiation resistance.
Objective 6.2.5: Determine if radiation protection will be required for organisms/ecosystems to survive and adapt beyond Earth.
Objective 6.2.6: Determine the critical components of an atmosphere (including water), their concentrations and interactions required to provide an atmospheric compatible with organism/ecosystem survival and adaptability beyond Earth, e.g. O2, CO2, N2, trace gases.
Objective 6.2.7: Determine the composition of an atmosphere that can be generated by a minimal ecosystem exposed to a Mars-like environment.
Objective 6.2.8: Determine the gases that must be added or scrubbed for survival and adaptation of that ecosystem beyond Earth.
Objective 6.2.9: Determine the temperature compatible with organism/ecosystem survival and adaptability beyond Earth.
Objective 6.2.10: Determine the temperature (and pressure) increases necessary to allow the most adaptable Earth ecosystem to survive on the Martian surface.
Objective 6.2.11: Determine the cellular changes that occur when organisms experience extreme changes in temperature (e.g. Mars).
Objective 6.2.12: Determine the changes that occur when organisms experience changes in pressure, i.e., that experienced at the surface of the Earth owing to the weight of a column of the atmosphere.
Objective 6.2.13: Determine the role of acidity and alkalinity in evolution of life.
Objective 6.2.14: Determine the importance of the interaction(s) of physical environmental factors on evolution.
Goal 6.3: Define the phenotypic and/or genotypic changes that allow organisms to flourish beyond the home planet.
Objective 6.3.1: To identify and understand the adaptive mechanisms/reproductive strategies that will allow organisms to survive and then adapt beyond the home planet (i.e., extreme environments)(requires input from question: How do rapid changes in the environment affect emergent ecosystem properties and their evolution?).
Objective 6.3.2: Determine the mechanisms which enable survival and adaptation of increasingly complex life/ecosystems in a Mars-like environments. Start with microbial organisms living in extreme environments as terrestrial environments that are too hostile (hypersaline, hyperarid, hyper-sedimentary) or too isolated (Antarctic dry valley lakes) for more complex life forms, have only microbial life.
Objective 6.3.3: Determine the biological mechanisms for surviving and adapting to environmental extremes such as those found on the surface of Mars (i.e., decreased gravity, increased radiation, low temperature, low pressure, altered atmospheric composition, etc.).
Objective 6.3.4: Determine the rate and duration of change in environmental parameters that allow for survival in unique environments.
Objective 6.3.5: Determine if the mechanisms that allow for adaptation to environmental extremes are the same mechanisms used for readapting to environmental norms.
Objective 6.3.6: Identify and understand the changes that occur in organisms after multiple generations beyond the home planet. Determine if these change preclude readaptation to the home planet.
Goal 6.4: Establish ethical principles for seeding life elsewhere in the solar system.