of energetic particles expelled from the solar surface are all amenable to investigation by means of satellite-borne and space-probe-borne instruments.

The first Orbiting Solar Observatory, OSO I, was launched on March 7, 1962. In the first 8 months of its operation, this Observatory provided the scientist with thousands of times more ultraviolet and X-ray data than had been obtainable hitherto using sounding rockets. Even today, OSO I continues to operate, although in limited fashion, returning usable scientific data to the scientist on the ground. These detailed studies of the sun are important in developing an understanding of solar flares and other solar activities that discharge particles and magnetic fields into the interplanetary medium.

The interplanetary medium (see fig. 3) must be understood before we commit men to long trips out to the moon or planets. This medium consists normally of 5 to 15 particles per cubic centimeter at our distance from the sun. It is through this interplanetary medium that the sun dispatches solar cosmic rays toward the

earth, which are hazardous and may even be lethal to crews and components of spacecraft.

The interplanetary medium is the region through which the sun exerts its influence on the earth, giving rise to our weather, creating the ionosphere and the auroras, stirring up the radiation belts and causing magnetic storms, and at times completely disrupting radio communications on the surface of the earth.

Because of Explorer satellites, Pioneers, especially Pioneer V, and Mariner II, the interplanetary medium is no longer the complete mystery that it once was. Nevertheless, there is much yet to be learned about it, and the NASA program includes a vigorous plan of attack on the problems of understanding interplanetary space and the role it plays in transmitting solar influences to the earth. To the scientist, this interplanetary space appears as a gigantic laboratory affording the opportunity to investigate matter and magnetic fields under conditions of low density that are absolutely unobtainable in the laboratory.

MOON AND PLANETS

The moon offers all kinds of scientific and engineering opportunities (see fig. 4). As the target of our manned lunar landing program, it brings to focus an engineering effort that exceeds in scope and daring all previous engineering ventures of mankind.

In the field of science, the moon is of particular interest because it may furnish one of the most significant clues to the question of how the earth and other planets of the solar system originated. The lunar surface is likely to have preserved the record of past events going back billions of years, perhaps nearly to the time of its origin 42 billion years ago. This record has remained unmarred by the erosion of atmospheres and oceans, and from the appearance of the moon as seen through telescopes, has been unchanged by mountain-building processes. On the earth, and probably also on Mars and Venus, the surface record is lost because of

these atmospheric and mountain-building processes.

Mariner has opened up the field of planetary sciences for the United States, as Lunik has already done for the U.S.S.R. in lunar investigations. The opportunities that lie ahead will be of interest to many disciplines in addition to astronomy, but should be especially attractive to the geophysicist. Most of the techniques that will be required to observe and make measurements on these bodies will be those of the geophysicist. Most of the instruments will be adaptations of geophysical instruments, and the scientists who press forward with these lunar and planetary investigations will be, in effect, geophysicists whether or not they call themselves such.

These forthcoming opportunities not only extend the range of the geophysicist's investigations to other planets, but also broaden the perspective in which he can view the earth.

Comparative investigations of earth, moon, and planets will contribute greatly to the understanding of each one; and also to the understanding of the whole solar system.

STARS AND GALAXIES

As the oldest of the sciences, astronomy has had an illustrious history. From ground-based observations that have been limited to the very narrow range of wavelengths in the visible portion of the spectrum, plus small extensions into the ultraviolet and the infrared, the astronomer has put together a truly remarkable body of astronomical knowledge and theory. More recently the huge radio telescope has permitted observations in the radio wavelength portion of the spectrum.

Nevertheless, astronomical theory itself indicates that the limitation of observation to the visible and part of the radio portions of the spectrum is a very serious limitation indeed.

According to theory the most fundamental processes in the birth of stars can be observed only in the infrared, while the most exciting portions of the evolution of the star are observable only in the ultraviolet. For this reason, the satellite orbiting above the earth's atmosphere opens up exciting new opportunities to the astronomer.

One of the most important programs in NASA involves the Orbiting Astronomical Observatory, designed to exploit these new opportunities in astronomy. Carrying instruments and telescopes above the earth's atmosphere, OAO will permit observations in all parts of the spectrum. The importance of being able to do this is illustrated in some measure by the inset in the lower right corner of figure 5. Here the same object, the Crab Nebula, is shown photographed in blue, yellow, red, and infrared wavelengths. The differences are quite apparent, but actually are much less marked than differences to be observed when observa

tions are made in the ultraviolet and X-ray wavelengths.

An additional new opportunity available to the astronomer is that of observing bodies of the solar system at close range. The lunar and planetary probes provide this opportunity for the planets of the solar system. In the course of time, probes directed to the vicinity of the sun itself will permit extremely valuable closeat-hand observations of our nearest star.

Still a third opportunity open to the astronomer and cosmologist is that of being able to perform experiments on a scale utterly unobtainable on the surface of the earth. By using spacecraft in satellite orbits about the earth or on escape trajectories from the earth, controlled or semicontrolled experiments can be performed on relativity, gravity, celestial mechanics, galactic cosmic rays (the origin of

which is still unexplained) and other topics which will add grist to the cosmologist's and cosmogonist's mill.

LIFE IN SPACE

Certainly one of the most exciting possibilities in space exploration is that indigenous life may be found outside the earth. The most likely candidate is Mars, where balloon observations in the infrared have detected emissions characteristic of the carbon-hydrogen bonds. While this does not prove the existence of life on Mars, it is most certainly highly provocative. For this reason, preparations are going forward with various types of instruments to search for living forms on the Red Planet. These will be carried in fly-bys and landers as soon as the necessary transportation is available.

All data available at present would indicate that there is little likelihood of life on Venus. Various radio astronomical observations of the planet indicate that the surface temperatures are in the vicinity of 700° K, well over the boiling point of water. These temperatures have been confirmed by the recent results from Mariner II. Taken in conjunction with the probably very high pressures existing on Venus, exceeding 20 atmospheres at the surface, such temperatures indicate that the entire planetary surface must be bathed in a searing atmosphere and that there is no chance of life there. The biologists insist, however, that there may yet be life on Venus, existing in the cooler upper atmosphere. Balloon samplings are being made of the earth's upper atmosphere to search for organisms that might be living there. Results from these investigations have already shown that there are such organisms living in the earth's upper atmosphere. These investigations may shed additional light on how much of a point the biologists have in connection with Venus.

It does not appear likely that there are living forms on the surface of the moon, because of the lack of an atmosphere, the lack of any observable water, the extreme temperature ranges to which the lunar surface is subjected, and the constant bombardment of the surface by highly energetic electromagnetic and particle radiations. Some scientists believe, however, that there might be living forms existing at some distance below the hostile lunar surface.

At any rate, it is clear that we must be very careful about what we do in the case of Mars. It is NASA policy, in the investigation of Mars, to protect by all possible means the opportunity that Mars may present to study nonterrestrial life forms. This includes sterilizing any space probes that are sent to Mars so as to prevent infection and contamination of the planet with terrestrial life forms and materials.

If the planet Mars is to be maintained as an ecological preserve, this can be done only by international cooperation. At the present time, this means specifically cooperation between the U.S. and the U.S.S.R.

In the case of the moon, we shall take advantage of the hostility of the lunar surface

to assist us in protecting the biological opportunities that may exist there. Lunar spacecraft, although not absolutely sterile, will be maintained at operating-room cleanliness. Whatever organisms remaining on the spacecraft do land on the moon will then be prevented by nature itself from spreading. Thus, the hostility of the lunar surface will then be relied on to prevent any spread of infection, and, indeed, to sterilize the landed object in the course of time.

It may well be that there is no extraterrestrial life to be discovered in the solar system. Nevertheless, that does not end our interest in life in space, because we, ourselves, are certainly going to put life out there. Indeed, we have already begun to do this in our Mercury program, as the Russians have in their Vostok program. Thus, one very important aspect of life in space concerns the influence of the space environment and space flight environment on terrestrial organisms.

In satellites and space probes, there will be the opportunity to study the effects of weightlessness, radiation, new periodicities, and other conditions strange to terrestrial life. Man himself will be one of the major objects of study

THE ENVIRONMENT OF SPACE

The scientific investigation of space, the effort to develop practical applications of space knowledge and technology, and the program to develop the ability of man to fly through space all direct attention to the environment of space as one of the most important of space phenomena. There are at least two aspects of our investigations of space environment: first, the scientist's desire to get the whole picture; and, second, the engineer's need to know what men and equipment are encountering when they go out into space.

Although their motivations may be different, the scientist and the engineer need to know the same things. Solar wind, plasmas in space, cosmic rays, the interplanetary magnetic field, solar fields, solar flares and particle eruptions, and planetary fields must be known to the scientist in detail in order that he can work out a theory of what is happening. The same quantities must be known to the engineer who is con