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Executive Summary
OVERVIEW
This report reviews the current state of the study of chemical evolution
and planetary biology and discusses the probable future of the field, at least
for the near term. To this end, the report lists the goals and objectives of
future research and makes detailed, comprehensive recommendations for
accomplishing them, emphasizing those issues that were inadequately dis-
cussed in earlier Space Studies Board reports.
The area of study described by the term "planetary biology and chemical
evolution" is necessarily broad, incorporating a wide spectrum of disci-
plines from astronomy to paleobiology to comparative planetology. Despite
their seemingly disparate natures, these disciplines are, in the present con-
text, closely interrelated. The different elements of planetary biology and
chemical evolution constitute an integrated whole; they can be viewed as a
continuum in which the areas of study are interconnected by one overarch-
ing goal: to understand the evolution of living systems. What brings this
field within the domain of the space sciences is its explicit reliance on
spacecraft and space technology for the pursuit of this major goal.
Chapter 2 discusses the evolutionary history of the biogenic elements.
The goal of research in this area is to understand the nature of the chemical
and physical transformations of these elements, from their nucleosynthesis
in stars to their ultimate incorporation into planetary bodies. Chapter 3
discusses a cardinal problem in the history of biological evolution, elucidat-
ing the processes by which materials came together on the primordial Earth
to form the first living organisms. The current status of the field of biologi-
cal evolution and recommended future research in that area are detailed in
Chapter 4. Chapter 5 discusses the evolutionary context of the first repli-
1
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2
THE SEARCH FOR LIFE'S ORIGINS
eating system on this planet and identifies gaps in the present knowledge.
In Chapter 6, the detection of extrasolar-system planets is considered from
an exobiological point of view.
As this report attempts to show, research in chemical evolution and plane-
tary biology is addressing one of the most fundamental and historically
persistent questions: how did living things come to be on this planet? In
effect, this report, then, assesses the status of our knowledge concerning the
history of living things from prebiological epochs to the present. The rec-
ommendations in Chapter 7 delineate specific research objectives over the
broad range of disciplines that constitute this field of scientific research,
and Chapter 8 discusses policy issues related to these recommendations.
THE COSMIC HISTORY OF THE BIOGENIC
ELEMENTS AND COMPOUNDS
From a terrestrial perspective, it is difficult to conceive of life forms in
which the elements hydrogen, carbon, oxygen, nitrogen, sulfur, and phos-
phorus do not play a predominant role. That they do indeed play such a
role throughout the universe seems highly probable because (apart from
phosphorus) these are among the most abundant elements throughout the
cosmos and, moreover, their chemistry is particularly well suited to the
development of the complex structures and functions characteristic of living
systems. Since the Sun and planets formed approximately 4.6 billion years
ago in a universe whose age is perhaps 15 billion years, these "biogenic
elements" have experienced a long and complex chemical history before
being incorporated into terrestrial biochemistry.
Knowledge of the chemistry and physics of both interstellar clouds and
the solar nebula will provide us with critical knowledge on how and from
what materials the solar system formed. In addition, there is increasing
evidence for the survival of interstellar molecular material within objects
present in the solar system today, such as interplanetary dust particles,
asteroids, meteorites, and comets.
The cosmic history of the biogenic elements and their compounds thus
becomes a critical field of study for exobiologists. An overriding goal of
this phase of the history of chemical evolution has been identified by the
committee as to understand the history of physical and chemical transfor-
mations undergone by the biogenic elements and compounds from nucleo-
synthesis to their incorporation and subsequent modification in preplanetary
bodies. This goal can be attained by fulfilling five major objectives:
· Determine the extent and evolution of molecular complexity in inter-
stellar and circumstellar environments;
· Determine the composition, structure, and interrelationships among
circumstellar, interstellar, and interplanetary dust;
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EXECUTIVE SUMMARY
.
Assess the efficacy of chemical and physical processes in the solar
nebula for altering preexisting materials and producing new compounds and
phases containing the biogenic elements;
· Determine how the formation and evolution of primitive bodies modi-
fied the distribution, structure, and composition of preexisting compounds
and solid phases containing the biogenic elements; and
· Determine the distribution, structure, and composition of presolar and
nebular products in existing primitive materials in the solar system.
The research necessary to achieve this goal will require extensive inter-
actions among investigators studying the origins of molecules that ulti-
mately become the precursors for biology, as well as collaborative partici-
pation of the astronomical, astrophysical, and planetary science communi-
ties in planning and executing research strategies related to this goal.
EARLY PLANETARY ENVIRONMENTS: IMPLICATIONS FOR
CHEMICAL EVOLUTION AND THE ORIGIN OF LIFE
A comparative study of planets is essential to an understanding of the
relationship between planetary development and the origin and evolution of
living systems. As a minimum, for life to arise and evolve on a planet, the
presence of liquid water and a hydrological cycle operating in concert with
geochemical cycles of the biogenic elements seem to be necessary. In a
more general context, the organic chemistry of planetary environments is an
extension of the cosmic evolution of the biogenic elements into the plane-
tary epoch. Knowledge of the processes that produce organic matter wher-
ever it occurs in the solar system is central to understanding chemical evo-
lution. The committee has identified two major goals for studies of early
planetary environments.
The first goal is to understand the processes responsible for the chemical
evolution of organic matter in the outer solar system. Attainment of this
goal can be achieved by the following objectives:
· Determine the origin and distribution of organic matter and disequili-
brium products containing the biogenic elements in the hydrogen-rich at-
mospheres of the outer planets;
· Elucidate the organic chemistry and the origin of carbon oxides on
Titan; and
· Characterize the organic matter on the dark surfaces of the asteroids,
satellites, and planetary rings of the outer solar system.
The second goal is to understand how the conditions for chemical evolu-
tion and the origin of life were influenced by the physical and chemical
development of the terrestrial planets. This goal can be attained through
the following objectives:
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4
THE SEARCH FOR LIFE'S ORIGINS
· Determine when and how the volatile elements necessary for life were
added to the surface regions of the Earth;
· Constrain the conditions on the early Earth for determining the timing
and probable environments for the origin and maintenance of the first or-
ganisms; and
· Assess the isotopic, molecular, morphological, and environmental evi-
dence for chemical evolution and the origin of life on Mars.
THE ORIGIN OF LIFE
What sparked the origin of life on the early Earth? Sources of informa-
tion that may shed light on this question are the record of the early solar
system as preserved in comets, asteroids, the Moon, and Mars; the geologi-
cal record; the paleogeological record of ancient microorganisms and their
physiological activity; and the history recorded in nucleotide and amino
acid sequences found in living cells (molecular phylogeny). Stromatolitic
formations in Western Australia and South Africa, at 3.5 billion years old,
contain the earliest solid evidence of life on Earth, but scientists are looking
for even earlier signs of life.
The study of the origin of life on Earth, a highly interdisciplinary en-
deavor, can be pursued in the field and in the laboratory by using two
approaches: laboratory simulations and examination of the natural records
of early solar-system events. The following are examples of the two ap-
proaches:
· Model systems for synthesizing fundamental biochemical monomers,
to deduce the composition of Earth's early atmosphere;
· Comparative molecular biology, to deduce the characteristics of early
cells by studying contemporary organisms;
· Models for replication;
· Models for the origin of gene expression; and
· Comparative planetology studying the Moon, Venus, and Mars to
help reconstruct the early history of Earth.
The committee has identified four goals to be pursued in studying the
origin of life. The first is to understand the origin and evolution of metabo-
lism in primitive life forms. This goal can be fulfilled by working toward
the following objectives:
· Reexamination of the prebiotic origin of biomolecules in environments
suggested as probable on the primitive Earth;
· Exploration of mechanisms for sequestering biomolecules on a sur-
face or within vesicles studies should lead to plausible prebiotic mecha-
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EXECUTIVE SUMMARY
s
nisms for the synthesis of molecules that could have formed vesicles, an
important step toward understanding the origin of cellular metabolism;
· Identification and characterization of chemical systems capable of
coenzyme functions in a prebiotic context; and
· Investigation of the nature of the earliest type of cellular metabolism.
The second goal is to understand the origin and evolution of replication,
the process that is the essence of life. This goal can be fulfilled by working
toward the following objectives:
.
A search for simple organic replicating systems template-directed
replication using ribonucleotides is the most straightforward general model
of replication, but even simpler systems warrant experimental study;
· Investigation of the possible role of ribonucleic acid (RNA) catalysis
in replication the isolation, sequencing, and study of small RNAs from the
widest possible diversity of cells may provide new insights into the funda-
mental role of RNA in replication; and
· Determination of the mechanism of clay formation in nature and in
the laboratory, and the possible relevance of clay to replication the min-
eral theory of the origin of life postulates the existence of clay particles that
have surface structures able to catalyze the organic reactions necessary to
initiate organic life, and that can replicate as well.
The third goal is to understand the origin and evolution of gene expres-
sion. The complex system of ribosomes, transfer RNAs, and aminoacyl-
transfer RNA synthetases has proven difficult to model. Comparative mo-
lecular studies of existing systems will be necessary to gain insight into the
essential workings of this translation process and of the genetic code. This
goal can be fulfilled by working toward the following objectives:
· Determination of the origin of codon assignments;
· Understanding the molecular mechanics of translation; and
· Phylogenetic-comparative dissection of the translation apparatus.
The fourth goal is to determine evolutionary events leading to the accre-
tion of complex genomes. This goal may be fulfilled by working toward the
following objective:
· Elucidation of the organization and interrelationships of phylogeneti-
cally diverse genomes.
It is clear that a major commitment for genome analysis will require
support from many federal agencies besides the National Aeronautics and
Space Administration (NASA); however, important aspects of this under-
taking are within the purview of NASA's Exobiology Program.
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6
THE SEARCH FOR LIFE'S ORIGINS
THE EVOLUTION OF CELLULAR AND MULTICELLULAR LIFE
From an exobiological perspective, biological evolution is a cosmic phe-
nomenon born of galactic and solar-system processes and influencing the
development of planetary surfaces. Increasing evidence supports the con-
cept of life intimately linked with the planet through biogeochemical cycles.
The origins and evolution of life on Earth have been influenced strongly by
events in the evolution of the physical Earth and also by extraterrestrial
phenomena such as meteoritic bombardments. For example. recent theo-
retical calculations indicate that a giant impact on Earth with a Mars-sized
object could have been responsible for the origin of the Moon and removal
of the early Earth atmosphere. The effect of such an event on the origin of
life on Earth (and elsewhere) is unclear but probably depends on the timing
of the impact, the composition of the early atmosphere, and the composition
of the secondary atmosphere that subsequently evolved.
A more integrated understanding of Earth's biological and physical his-
tory is necessary to understand the evolution of terrestrial life. As biologi-
cal systems on Earth became more complex, they exerted greater influence
on both their own development and that of the planet. The transition from
physical to biological evolution of organic matter is expected to character-
ize all planets whose early physical evolution is comparable to Earth's.
Recent data support the view that all extant organisms on Earth de-
scended from a common ancestor, with the three principal lines of evolu-
tionary descent being the archaebacteria, eubacteria, and eukaryotes. All
living organisms contain an extensive record of their own phylogenetic
history, and molecular phylogeny should provide insight into much of this
history.
The committee has identified four goals for future research on the evolu-
tion of life, all appropriate for NASA sponsorship; NASA can play a criti-
cal role in coordinating and catalyzing the necessary interdisciplinary re-
search. The first goal is to develop a universal understanding of the tempo-
ral sequence and evolutionary relationships of life on Earth. This goal may
be fulfilled by studying a wide variety of organisms with the techniques of
molecular phylogeny and biochemical and morphological characterization.
The second goal is to determine the properties of the universal ancestor
of extant organisms. This goal may be fulfilled by rooting the universal
phylogenetic "tree." Studies of molecular phylogeny have brought this tree
within reach; besides providing the starting point for studying the course of
biological evolution within the three primary kingdoms, this set of phylo-
genetic relationships provides a framework for investigating life's history
prior to the segregation of the three extant lineages. A principal objective
of this line of research should be the recognition and evolutionary evalu-
ation of gene families.
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EXECUTIVE SUMMARY
7
The third goal is to understand what factors drive the biosphere. Bio-
logical evolution has been affected by Earth's cosmic environment, and mo-
lecular phylogeny suggests that evolution proceeded in bursts. Biological,
tectonic, and environmental changes appear to be closely interrelated. This
goal may be fulfilled by integrating the biological accounting of the Earth's
historical development with that obtained from studies of geological rec-
ords and determining the influence of Earth's cosmic environment on evo-
lution.
The fourth goal is to generalize our understanding of environmental and
early cellular evolution on Earth by comparative studies of Mars. This
goal may be fulfilled by investigating the sedimentary record of Mars for
signs of biogeochemical activity.
SEARCH FOR LIFE OUTSIDE THE SOLAR SYSTEM
Life as we know it is a planetary phenomenon, requiring interactions
among liquid water, gaseous atmosphere, minerals provided by the plane-
tary surface, energy from the Sun, cosmic radiation, volcanic activity, and
other sources. The oxygen-rich nonequilibrium chemistry of our atmosphere
and electromagnetic radiation "leaking" from our planet are signs that life
exists on Earth. As an example, the detection of such phenomena could be
a key strategy in the search for life on other planets.
The committee has identified the goal as follows: to understand the na-
ture and distribution of life in the universe. No unambiguous evidence of
extrasolar planetary systems exists, although many tantalizing clues have
been found; observational verification that other planetary systems have
formed around other stars should be possible in the coming decade. The
search for extrasolar planets is important to achieving this goal because life
on Earth is only a single example from which it is impossible to generalize.
In parallel with the search for passive evidence of life beyond our solar
system, the search for evidence of technologically advanced civilizations
should proceed. NASA is the leading agency in the development of most, if
not all, of the detection instrumentation required for both types of searches.
To fulfill the goal of understanding the nature of the distribution of life
in the universe, the committee recommends pursuing the following objec-
t~ves:
· Determination of the frequency and morphology of nearby planetary
systems this will require a new generation of instruments capable of de-
tecting low-mass planets and investigating solar-system-scale phenomena
within protoplanetary disks in nearby regions of star formation;
· Determination of the frequency of occurrence of conditions suitable to
the origin of life obtaining information on the surface temperature and
atmospheric chemical composition of extrasolar planets requires direct im-
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8
THE SEARCH FOR LIFE'S ORIGINS
aging and spectroscopic analyses, and the technology required for such
observations is not yet available;
· Search for presumptive evidence of life in other planetary systems;
and
.
Search for evidence of extraterrestrial technology.
MAJOR RESEARCH RECOMMENDATIONS
The recommendations in Chapter 7 fall into two general categories: those
that require observations and experiments to be conducted on either plane-
tary missions or facilities in Earth orbit, and those that include observa-
tions, experiments, and theoretical modeling studies that can be carried out
in ground-based facilities. In view of the generally large differences in cost
and complexity between these two categories, the committee assigns priori-
ties within the two groups separately. Within each group, lists have been
priority ordered on the basis of a combination of near-term feasibility and
. . . .
scientific Importance.
Recommendations Requiring Flight Opportunities
Mars
The highest priority in the category requiring flight missions is accorded
to studies of Mars. It is hard to imagine more exciting and fundamental
questions than those concerning the early surficial environment and the
possibility of chemical or even biological evolution on the early surface of
our neighboring planet. Furthermore, Mars is the only other object in the
solar system on which an earlier origin of life could have left a well-
preserved, exposed record. Sedimentary rocks on Mars may contain a rec-
ord of the interval in chemical evolution that is nowhere preserved on the
Earth and may thus contribute to understanding the processes that led to the
origin and early evolution of organisms on this planet. Thus, investigations
of Mars can contribute to the elucidation of objectives discussed previously
in connection with early planetary environments and the origin of life-
both on the Earth and, possibly, on Mars as well as with the course of
biological evolution on this planet. The committee therefore recommends
studies to
· Conduct chemical, isotopic, mineralogical, sedimentological, and pale-
ontological studies of Martian surface materials at sites where there is evi-
dence of hydrologic activity in any early clement epoch, through in situ
determinations and through analysis of returned samples; of primary inter-
est are sites in the channel networks and outflow plains; highest priority is
assigned to sites in which there is evidence suggestive of water-lain sedi-
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EXECUTIVE SUMMARY
9
meets on the floors of canyons as in the Valles Marineris system, particu-
larly Hebes and Candor chasmata; and
Reconstruct the history of liquid water and its interactions with sur-
face materials on Mars through photogeologic studies, space-based spectral
reflectivity measurements, in situ measurements, and analysis of returned
samples.
.
Comets and Asteroids
Critical information about the chemical nature, and early processing, of
materials containing the biogenic elements (i.e., the evolution of organic
complexity in the solar nebula) can be obtained from the study of these
relatively unmetamorphosed materials of the solar system. Such studies can
lead to an understanding of the role of these bodies in supplying the primi-
tive Earth with the organic constituents and volatiles necessary for the ori-
gin of life on the planet. Furthermore, these bodies are also of interest as
projectiles that may have had significant effects on the course of biological
evolution by impacting the Earth. The committee therefore recommends
that
· Measurements be made, by remote spectroscopic observations and in
situ, of the elemental and isotopic composition of cometary comae and
nuclei and of the principal asteroid types, including determination of the
molecular composition of components containing the biogenic elements
hydrogen, carbon, nitrogen, oxygen, phosphorus, and sulfur in comets and
primitive asteroids; such measurements should be made at various surface
locations and depths to determine the degree of homogeneity; and
· A cometary sample be obtained for detailed laboratory analysis of
atmospheric, surface, and subsurface materials.
Titan and the Giant Outer Planets
The outer planets, in contrast to the inner, represent bodies with atmo-
spheres dominated by hydrogen and containing organic constituents. Study
of these objects can yield considerable insight about the processes involved
in the formation of organic compounds under natural conditions in a hydro-
gen-rich environment. Much interesting chemistry must also be taking place
in the strongly reducing atmosphere of Titan. Thus, investigations of these
objects can be expected to shed much light on one model for the formation
of life on the Earth, in which a reducing atmosphere has been invoked. The
committee therefore recommends studies to
· Identify the compositions, and measure the abundances and distribu-
tions, of gaseous organic compounds and organic haze particles in Titan's
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TlIE SEARCH FOR LIFE'S ORIGINS
atmosphere by using atmospheric entry probes and remote astronomical
observations.
· Elucidate the distribution, with altitude, of organic matter, carbon
monoxide, and phosphine in the atmospheres of Jupiter and Saturn by using
atmospheric entry probe measurements and astronomical observations.
The Interstellar Medium and Cosmic Dust Particles
The earliest stages of chemical processing involving the biogenic ele-
ments are taking place in molecular clouds and protosolar nebulae. Studies
of these objects can therefore answer fundamental questions about the early
history of organic chemical evolution. For investigation of the interstellar
and protostellar regions, significant advances in our understanding of early
organic chemical evolution can be realized by opening up those portions of
the infrared- through millimeter-wavelength spectrum for which the atmo-
sphere is opaque. Additional opportunities to increase understanding of pro-
cesses and events in the evolution of volatiles and organic materials in the
early solar system can be attained by the study of extraterrestrial dust par-
ticles. For effective probing of these scientific issues, the committee
Strongly supports the development of high spectral resolution, Earth-
orbital facilities for astronomical observations at infrared, submillimeter
and millimeter wavelengths; arid
· Recommends Earth-orbital collection of interplanetary (and potentially
interstellar) dust particles including, ultimately, nondestructive methods
of collection to allow their detailed chemical and isotopic analysis.
Recommendations Requiring Ground-Based Studies
Chemical Evolution and the Origin of Life
Scientific developments over the past decade that bear on the processes
leading to the origin of life have resulted in an expansion in emphasis from
prebiotic chemistry into biochemical evolution as well. One consequence
of this expansion is that work of high interest to the exobiology community,
and supported by NASA, has increasingly come to overlap studies sup-
ported by other federal agencies such as the National Institutes of Health
(NIH) and the National Science Foundation (NSF). NASA's continuing
support is critical, however, because only it provides the programmatic
integration that promotes the necessary cross-fertilization of the various
disciplines relevant to exobiology. As in the past, NASA programs in this
field should strive to avoid duplicating the efforts of other agencies and
should complement the work of these agencies by focusing on issues that
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EXECUTIVE SUMMARY
11
directly concern interactions between the physical and chemical environ-
ments that led to the development and evolution of organisms on this planet.
Accordingly, the committee recommends
The reexamination of biological monomer synthesis under primitive
Earth-like environments, as revealed in current models of the early Earth,
and the synthesis and study of simple model systems for fundamental bio-
logical processes such as polynucleotide replication, sequestration of bio-
molecules, coenzyme functions, and elements of the translation system in
protein syntheses;
.
The development of improved data on the biological and physical
development of the Earth by modeling the geochemistry of the prebiotic
and earliest biotic oceans to obtain their composition and their physical and
chemical responses to large impacts, and by careful sedimentological, geo-
chemical,~and paleontological analysis of ancient sedimentary basins; local
environments favorable to the origin of life should be identified and charac-
terized geophysically and geochemically: geological research should be aimed
not only at the elucidation of environmental evolution but also at under-
standing the cosmic influences on terrestrial environments and evolution;
.
Studies designed to recognize extraterrestrial signatures in sedimen-
tary successions and research to evaluate temporal patterns in the composi-
tion of the biota (as recorded in the fossil record) in light of recognizable
extraterrestrial signals;
· The continued search on Earth for igneous and sedimentary rocks
formed prior to 3.8 billion years ago; and
· The development of robust phylogenies relating living organisms,
through the comparison of sequences in informational macromolecules,
especially small subunit ribosomal RNAs, and the elucidation of the bio-
chemical and ultrastructural characters of microorganisms in order to relate
patterns of phenotypic diversity to phylogeny.
Mars-Related Studies
Ground-based studies are necessary to understand present environmental
conditions in order to plan effective exploratory investigations related to
exobiology. The committee therefore recommends that
· Laboratory and theoretical model studies be carried out of photochemi-
cal and weathering processes on Mars that will determine the nature of
inorganic carbon, nitrogen, sulfur, and iron-bearing phases in Martian sur-
face soils, will indicate the geochemical cycles of these elements during an
earlier aqueous epoch, and will characterize the nature of the oxidants re-
vealed by the Viking experiments; and
· Scenarios be developed for chemical evolution and the origin of life
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THE SEARCH FOR LIFE'S ORIGINS
on Mars, based on our knowledge of these processes on Earth, but bounded
by existing data and theory on the accretionary, tectonic, geologic, and
climatic history of Mars.
Studies Related to Comets and Asteroids
These bodies of the solar system are of interest to the field of exobiology
from many points of view: as projectiles impacting the planets, as possible
sources for the biogenic elements and volatiles on the terrestrial planets,
and as reservoirs of information about the early history of the solar system.
In relation to these issues, the committee recommends
· The maintenance of a vigorous program of research on the chemical,
isotopic, mineralogical, and petrographic properties of meteorites and labo-
ratory studies of the molecular and isotopic compositions and yields of
organic molecules produced in realistic simulations of those astrophysical
environments within which presolar constituents of carbonaceous meteor-
ites may have been produced; and
· Theoretical studies on the physics of comet formation, to determine
the maximum size of comets accreted in the solar nebula, as well as ther-
mocalculations of the composition of atmospheres produced by large im-
pacts of cometary and various asteroidal-type bodies.
Studies Related to Titan and the Giant Outer Planets
Theoretical modeling and laboratory studies are required to elucidate the
organic chemistry in the atmospheres of Titan and the giant planets, as well
as to effectively interpret relevant data obtained from missions to these
objects. The committee therefore recommends that
· Simulations be carried out of organic synthesis resulting from the
deposition of electrons, photons, and cosmic rays into Titan's atmosphere
and that similar experiments, as well as computer simulations, be conducted
that will yield predictions of the molecular compositions and abundances of
organic matter produced by processes operating at various levels in the
atmospheres of Jupiter and Saturn.
Studies Related to the Interstellar Medium and Dust
Data from laboratory investigations and from theoretical modeling are
necessary to prepare for, understand, and extend the results obtained from
space-borne experiments aimed at studying the interstellar medium and dust
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EXECUTIVE SUMMARY
13
particles of interstellar and interplanetary origin. For these purposes, the
committee recommends
· Study of the spectra of, and chemical processes involving, potential
gas and grain constituents of molecular clouds that are the sites of star and
planetary formations, as well as study of gas and grain reactions under con-
ditions consistent with realistic models of the solar nebula, including a
variety of nonequilibrium processes, and of the growth and destruction of
grain aggregates;
· Utilization of ground-based telescopic facilities to probe the chemis-
try and physics of star-forming regions in detail, and development of the
instrumentation necessary to maximize the scientific return from space-
based, laboratory, and telescopic measurements, including broad-bandwidth,
high-resolution spectrometers, and microanalytical techniques;
· Maintaining a vigorous program of research on the chemical and iso-
topic properties of dust particles of extraterrestrial origins; and
· Theoretical modeling of chemical and physical processes, including
grain growth, in the solar nebula and in interstellar, circumstellar, and pro-
tostellar environments.
Studies Related to the Search for Life Outside the Solar System
Two parallel avenues of research should be pursued in attempts to detect
life beyond the solar system: searches for evidence of biological modifica-
tion of an extrasolar planet and searches for evidence of extraterrestrial
technology. These separate approaches can conceivably influence each other.
For example, if a nearby solar-type star is found to have a planetary system,
it would become a prime target in the search for extraterrestrial intelligence
(SETI); similarly, if a "SETI signal" were detected from the direction of
some nearby star, intensive efforts would undoubtedly be made to image
and study the host planet. Because both lines of investigation proceed si-
multaneously, the overall priorities listed below are those suggested natu-
rally by the existing maturity of the requisite instrumentation. For these
studies, the committee recommends
· Continued support for ground-based and earth-orbital searches for
extrasolar planets
· Commencement of a systematic ground-based search through the low
end of the microwave window for evidence of signals from an extraterres-
trial technology; and
· Studies leading to the development of future technologies for these
investigations, including large-scale optical, infrared, and submillimeter ar-
rays or monoliths in orbit or on lunar farside for imaging extrasolar planets
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THE SEARCH FOR LIFE'S ORIGINS
and protoplanetary nebulae; a dedicated SETI facility with radio frequency
interference (RFI) protection in high Earth orbit or on lunar farside; ad-
vanced data-processing techniques; and substantive original or unconven-
tional approaches to the detection of other technological civilizations.
SPACE SCIENCE PROGRAM AND POLICY ISSUES
Research in planetary biology and chemical evolution extends over many
"classical" scientific disciplines and brings together investigators from seem-
ingly disparate areas.
Over the last two decades, this field has developed to the point at which
evolutionary themes on cosmological, chemical, and biological levels have
become major foundations from which studies are undertaken. With these
common evolutionary themes and the exposition of continuous cause and
effect between evolving biological and planetary systems, communication
across scientific disciplines has become at least as important as that within
the disciplines themselves. Maintenance of this broad "mix" of biological
and physical sciences, and of ground- and space-based investigations, is
unique to the space sciences and critical to the effective conduct of a vigor-
ous national program in chemical evolution and planetary biology.
The current efforts of NASA in chemical evolution and planetary biol-
ogy are administered almost entirely by the Exobiology Program Office
within the Life Sciences Division of the agency. On the other hand, plan-
ning for, and implementation of, space missions not directly concerned with
space medicine or space biology are conducted by other divisions of NASA.
Although consideration has often been given to exobiology objectives in the
development of mission plans, much stronger interaction is needed between
mission planners and the exobiology science community. To enhance the
utility of future missions for those areas of inquiry that are the subject of
this report, the advice of qualified scientists should be utilized in the plan-
ning and implementation of these missions.
The committee also urges NASA to encourage the timely development of
instrumentation for potential use in space experiments involving planetary
biology and chemical evolution, well in advance of payload selection, by
setting aside specific funds for this purpose.
Because of the essential role of space technology in many aspects of
research in planetary biology and chemical evolution, almost all of the
support for this field, and for integration of its various elements, is now
borne by a single federal agency, NASA, through its grants and in-house
activities. Nevertheless, other federal agencies, notably the NSF and NIH,
support research that may be directly related to the overall goals of this
program. NASA should explore mechanisms for closer interaction with its
sister agencies in order to maximize national efforts, especially in areas that
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EXECUTIVE SUMMARY
15
might be jointly funded. Such interactions can serve to inform a much wider
circle of scientists than might otherwise be reached, of the goals, objec-
tives, and opportunities of the NASA programs in chemical evolution and
planetary biology and, at the same time, could bring new ideas and fresh
approaches into the field.
In this regard, the committee is conscious of the fact that potentially
interested scientists are often unaware of NASA's goals in this area. NASA
should devise ways to reach more broadly into the scientific community by
delineating and publicizing its goals and objectives and also by establishing
more clearly the procedures through which entry can be made into the
program.
It is also important for NASA to educate the scientific community about
the many areas of evolutionary biology in which data obtained from space
missions have enhanced understanding of the course of evolution. NASA
should make a greater effort to bring to the attention of the scientific com-
munity the potential benefits to be derived from the use of space technol-
ogy.
Because of the interdisciplinary nature of this field, there is an obvious
need for frequent and sustained cross communication among the various
disciplines that contribute to the overall goals of the program. To imple-
ment this need, NASA should establish procedures that will encourage more
effective communication among molecular/evolutionary/biospheric biologists,
paleontologists, astronomers, geologists, and planetary modelers both from
within NASA centers and from the academic community. Opportunities for
such interactions can be facilitated by NASA sponsorship of workshops,
symposia, and innovative interdisciplinary research projects.
Also, because the subject matter of this field cuts across both the physi-
cal and the biological sciences, specific training in this area is not normally
available to students as they prepare for their scientific careers, and young
people entering into the pool of scientific talent are less apt to seek careers
in chemical evolution and planetary biology. To surmount this deficiency,
NASA should develop a program of specific postdoctoral fellowships in the
field by which candidates would be able to pursue advanced studies either
at NASA in-house laboratories or with university specialists.
Representative terms from entire chapter:
biogenic elements
