Broca's Brain - Carl Sagan [86]
Going hand in hand with the improvement in the quantity of our information is the spectacular improvement in its quality. Prior to Mariner 4, the smallest feature reliably detected on the surface of Mars was several hundred kilometers across. After Mariner 9, several percent of the planet had been viewed at an effective resolution of 100 meters, an improvement in resolution of a factor of 1,000 in the last ten years, and a factor of 10,000 since Huygens’ time. Still further improvements were provided by Viking. It is only because of this improvement in resolution that we today know of vast volcanoes, polar laminae, sinuous tributaried channels, great rift valleys, dune fields, crater-associated dust streaks, and many other features, instructive and mysterious, of the Martian environment.
Both resolution and coverage are required to understand a newly explored planet. For example, even with their superior resolution, by an unlucky coincidence the Mariner 4, 6 and 7 spacecraft observed the old, cratered and relatively uninteresting part of Mars and gave no hint of the young and geologically active third of the planet revealed by Mariner 9.
LIFE ON EARTH is wholly undetectable by orbital photography until about 100-meter resolution is achieved, at which point the urban and agricultural geometrizing of our technological civilization becomes strikingly evident. Had there been a civilization on Mars of comparable extent and level of development, it would not have been detected photographically until the Mariner 9 and Viking missions. There is no reason to expect such civilizations on the nearby planets, but the comparison strikingly illustrates that we are just beginning an adequate reconnaissance of neighboring worlds.
THERE IS NO question that astonishments and delights await us as both resolution and coverage are dramatically improved in photography, and comparable improvements are secured in spectroscopic and other methods.
The largest professional organization of planetary scientists in the world is the Division for Planetary Sciences of the American Astronomical Society. The vigor of this burgeoning science is apparent in the meetings of the society. In the 1975 annual meeting, for example, there were announcements of the discovery of water vapor in the atmosphere of Jupiter, ethane on Saturn, possible hydrocarbons on the asteroid Vesta, an atmospheric pressure approaching that of the Earth on the Saturnian moon Titan, decameter-wavelength radio bursts from Saturn, the radar detection of the Jovian moon Ganymede, the elaboration of the radio emission spectrum of the Jovian moon Callisto, to say nothing of the spectacular views of Mercury and Jupiter (and their magnetospheres) presented by the Mariner 10 and Pioneer 11 experiments. Comparable advances were reported in subsequent meetings.
In all the flurry and excitement of recent discoveries, no general view of the origin and evolution of the planets has yet emerged, but the subject is now very rich in provocative hints and clever surmises. It is becoming clear that the study of any planet illuminates our knowledge of the rest, and if we are to understand Earth thoroughly, we must have a comprehensive knowledge of the other planets. For example, one now fashionable suggestion, which I first proposed in 1960, is that the high temperatures on the surface of Venus are due to a runaway greenhouse effect in which water and carbon dioxide in a planetary atmosphere impede the emission of thermal infrared radiation from the surface to space; the surface temperature then rises to achieve equilibrium between the visible sunlight arriving at the surface and the infrared radiation leaving it; this higher surface temperature results in a higher vapor pressure of the greenhouse gases, carbon dioxide and water; and so on, until all the carbon dioxide and water vapor is in the vapor phase, producing a planet with high atmospheric pressure and high surface temperature.
Now, the reason that Venus has such an atmosphere and Earth does not seems