scientific knowledge, but numerous practical satellite services not for this country alone, but for the whole world. It is in this same spirit of providing a focal point for international cooperation and support that we feel the U.S. can and should take the initiative in SETI.

The material, technological and intellectual resources of the U.S. are such that a large-scale SETI program could be carried on indefinitely by this country alone without appreciable drain on the economy. There are good reasons for believing the net effect on the economy could be positive. Even if international cooperation and support were slow to materialize, we believe SETI remains a feasible and worthwhile U.S. endeavor.

The psychology of and mechanisms for international cooperation suggest that an international SETI effort is unlikely until one big nation, such as the U.S., seizes the initiative and invites serious participation by others. It is in this sense of initiative and not in the pursuit of narrow national advantage that we recommend a leading role for the U.S. in SETI.

Initiating the SETI Effort

To carry on a significant United States SETI effort, public funds must be committed explicitly, with the approval of both the legislative and executive branches of the Federal Government. The evolution of an appropriate federal program lies with Congress and the President, but can only follow much preparatory work supported by one or more existing agencies.

We recognize that successful administration of the SETI program will require leadership by an agency with:

a.

b.

C.

a mandate to carry out scientific research and exploration, possibly requiring operations in space;

large scale project management experience;

the ability to successfully involve the U.S. and foreign scientific community in a large scale enterprise;

d.

in-house expertise in the relevant fields of technology; and

e.

long range goals compatible with SETI.

Since NASA clearly meets these criteria it is particularly appropriate for NASA to take the lead in the early activities of a SETI program. SETI is an exploration of the Cosmos, clearly within the intent of legislation that established NASA in 1958. SETI overlaps and is synergistic with long term NASA programs in space astronomy, exobiology, deep space communications and planetary science. NASA is qualified technically, administratively, and practically to develop a national SETI strategy based on thoughtful interaction both with the scientific community and beyond to broader constituencies.

SECTION II: COLLOQUIES

(These colloquies are general discussions on matters of central importance to SETI. Much of the discussion has been abstracted from the minutes of the meetings of the Science Workshops.)

1. COSMIC EVOLUTION

Through the centuries, man has continually searched the sky for clues to his destiny. His imagination has been captivated by the stars, his mind challenged by the mystery of their origin and extent, and his spirit imbued with a thirst for some understanding of his role in the cosmos.

Scientific discoveries in fields as diverse as astronomy and molecular biology have brought us, in the course of only the last 15 years, closer to solving three timeless riddles which many cultures have attempted to explain: How did the Universe begin and develop? How did life originate and evolve? What is our place and destiny in the Universe?

This burst of interdisciplinary discoveries has given rise to new concepts of the origin of life from inanimate material on the primitive Earth, of the formation of planets and stars, of the synthesis of fundamental particles of matter, and of the beginnings of the Universe itself: all seem to be founded on the same basic laws of chemistry and physics. The conclusion that the origin and evolution of life is inextricably interwoven with the origin and evolution of the cosmos seems inescapable. Taken in its totality, this pathway, from fundamental particles to advanced civilizations, forms the essence of the concept of cosmic evolution.

To be sure, the sequence from primordial fireball to matter to stars to planets to prebiotic chemistry to life and to intelligence, is incomplete and even controversial in some of its details. However, a broad picture is emerging, a picture that is both imaginative and illuminating.

The Universe appears to have begun as an awesome primordial fireball of pure radiation, commonly referred to as the "big bang," some 15 billion years ago. The totality of matter in the. Universe, probably in the form of the most fundamental particles in nature, namely electrons, protons and neutrons, was flung apart with tremendous speed. As the fireball expanded and cooled, thermonuclear reactions produced helium nuclei. Still further expansion dropped the temperature. to the point where hydrogen and helium atoms formed by combination of the electrons with the protons and helium nuclei, but elements heavier than helium were not produced in appreciable quantities. During later phases of the expansion, gravitational forces probably acted to enhance any nonuniformities of density that may have existed, and thus began the hierarchy of condensations that resulted in galaxies, stars, and, ultimately, planets.

Galaxies apparently had their origin in roughly spherical, slowly rotating, pregalactic clouds of hydrogen and helium which collapsed under their own gravity. When the contraction had proceeded sufficiently, stars began to form, and their rate of formation increased rapidly. The observed distribution of stellar populations agrees qualitatively with this general picture of contraction of the evolving galactic gas cloud.

Stars, like living organisms, are not immutable. They are born, evolve, and die. A star begins as a globular fraction of a larger gas cloud. The globule contracts under its own gravity, compressing and heating the gas to incandescence. The luminosity steadily increases as gravitational potential energy is converted into heat. When the internal temperature becomes high enough

to initiate nuclear reactions, the contraction stops: the star has entered the main sequence. When all its fuel is burned the star dies as a white dwarf or explodes as a supernova, depending on its

mass.

Although hydrogen and helium were created in the big bang, the rest of the elements were formed inside stars and in stellar explosions. Thus, every one of the heavier atoms in our bodies, including the oxygen that we breathe, the carbon and nitrogen in our tissues, the calcium in our bones, and the iron in our blood, was formed through the fusion of lighter atoms either at the center of a star or during the explosion of a star.

Stars spend 99 percent of their active lives burning hydrogen. When the hydrogen in the core is converted to helium, contraction begins. Core contraction releases enough energy to ignite helium which then burns to carbon. While all stars may eventually contribute to the production of carbon, nitrogen, and oxygen, and other elements up to and including iron, the heavier elements are probably made by neutron capture and beta decay inside massive stars during their final stages of evolution or when these stars explode as supernovae. Supernovae, then, may be the primary means by which the elements which are created in stars are recycled back into the interstellar medium. Out of the material sprayed around the galaxy by these explosions, somewhere else a new star with rocky planets can form.

The Milky Way galaxy is one of some 10 billion galaxies in the presently observable Universe, and our Sun is one of some 300 billion stars in the galaxy. The striking fact is that our galaxy and our Sun, to which we owe our very existence, are not unusual in any fundamental way compared with other galaxies and stars. Astronomical data indicate no peculiarities in origin, location, mass, luminosity, age, or other characteristics. Our Sun, therefore, is a relatively common type G dwarf star situated in a typical part of the disk of a rather typical spiral galaxy.

Discoveries made during the last 30 years have resulted in increased support for the nebular theory of the formation of planetary systems. According to this theory, development of the solar nebula was the result of the collapse of a large, rotating interstellar cloud whose inner portion was then heated by absorption of infrared radiation emanating from the proto-sun. At this stage, the cloud would be greatly flattened by its rotation and would consist of a disk with a denser, rapidly rotating, hot central region. Irregular density distributions in the disk are believed to have produced nucleation centers for the accretion of material into planets. In the outer regions of the disk most of the primordial gases of the disk probably went into forming the dense atmospheres of Jupiter-type planets. In the inner part of the disk, terrestrial-type planets may have formed early atmospheres which were then dissipated by the central star and replaced by outgassing from the planetary interiors; or they may have formed without atmospheres, the hydrogen and helium having been blown out of the inner solar nebula by the young Sun.

This renewed scientific support for the nebular theory of planetary formation has rekindled interest in the existence of extraterrestrial life because it predicts that stars with planetary systems should be the rule rather than the exception. In contrast to other theories, which attribute planetary formation to catastrophic events like star explosions or collisions, the nebular theory

suggests that formation of planets will usually accompany the formation of a star. This implies that the galaxy and Universe should be replete with potentially life-supporting planetary sites.

Planets around other stars have never been observed directly with telescopes because of the great brightness difference between the star and planet, and the proximity of their images. Indirect evidence for the existence of another planetary system has been obtained by observation of the motion of Barnard's star over a 30-year period, but is inconclusive. The oscillation in its movement which, if real, could be accounted for by the presence of a planet of roughly Jupiter's size may be only instrumental error. At the present time, techniques are being developed which, in the near future, may allow direct observation of extra-solar planets (see Section II-3).

If the planets did condense from the proto-solar disk, their initial composition might be expected to reflect that of the Sun. The atomic abundances of some of the elements found in the Sun are, in order: hydrogen (87.0 percent), helium (12.9 percent), oxygen (0.025 percent), and nitrogen (0.02 percent). It should be noted that, with the exception of helium, these are the very elements which constitute 99 percent of living matter.

The giant planets appear to have a similar composition; that is, less than 1 percent heavy elements and the remainder hydrogen and helium. Furthermore, Jupiter contains methane, water, and ammonia, the reduced forms of carbon, and oxygen and nitrogen, as would be expected based on thermodynamic properties of these elements in the presence of a large excess of hydrogen. Hence, the present Jovian atmosphere may be in fact its primitive atmosphere, retained for billions of years because of the planet's mass. The inner planets, on the other hand, are composed almost entirely of heavy elements. With their present masses, these planets cannot prevent hydrogen or helium from escaping. Hence, the Earth's primitive atmosphere may have been transitory, with a more stable atmosphere arising as a result of outgassing of the crust by volcanic action. Volcanos discharge large quantities of water vapor and carbon dioxide, some nitrogen, and other gases. The carbon dioxide and water could be reduced to hydrogen and methane by free iron present in the early crust, and hydrogen and nitrogen could combine to form ammonia. Therefore, the Earth's early atmosphere may have consisted mainly of hydrogen, nitrogen, methane, ammonia, water, and carbon dioxide, with small amounts of other gases. It is believed that chemical evolution leading to life on Earth began in such an environment some 4.5 billion years ago.

The theory of chemical evolution was contemplated by Darwin, conceptualized by Oparin and Haldane, and tested experimentally by Miller and Urey. Simply put, the theory proposes that release of energy in the Earth's primitive atmosphere by various mechanisms resulted in the synthesis of simple organic molecules, which in turn were converted into molecules of greater complexity. New chemical reactions gradually came into being as a result of the increasing complexity, and new chemical order was imposed on the more simple organic chemical relations. At some point in this process, the first self-reproducing molecules appeared.

The energy sources available for the synthesis of organic compounds under prebiotic conditions were ultraviolet light from the Sun, electric discharges, ionizing radiation, and heat. Most of these have now been used in laboratory simulations to produce a wide variety of organic molecules from the presumed primitive atmosphere of methane, ammonia, water, and hydrogen.