Broca's Brain (27 page)

Mariner 9 observations imply that the winds on Mars at least occasionally exceed half the local speed of sound. Are the winds ever much larger? What is the nature of a transonic meteorology? There are pyramids on Mars about 3 kilometers across at the base and 1 kilometer high. They are unlikely to have been constructed by Martian pharaohs. The rate of sandblasting by wind-transported grains on Mars is at least 10,000 times that on Earth because of the greater speeds necessary to move particles in the thinner Martian atmosphere. Could the facets of the Martian pyramids have been eroded by millions of years of such sandblasting from more than one prevailing wind direction?

The moons in the outer solar system are almost certainly not replicas of our own, rather dull satellite. Many of them have such low densities that they must be composed largely of methane, ammonia or water ices. What will their surfaces look like close up? How will impact craters erode on an icy surface? Might there be volcanoes of solid ammonia with a lava of liquid NH
₃
trickling down the sides? Why is Io, the innermost large satellite of Jupiter, enveloped in a cloud of gaseous sodium? How does Io help to modulate the synchrotron
emission from the Jovian radiation belt in which it lives? Why is one side of Iapetus, a moon of Saturn, six times brighter than the other? Because of a particlesize difference? A chemical difference? How did such differences become established? Why on Iapetus and nowhere else in the solar system in so symmetrical a way?

The gravity of the solar system’s largest moon, Titan, is so low and the temperature of its upper atmosphere sufficiently high that hydrogen should escape into space extremely rapidly in a process known as blow-off. But the spectroscopic evidence suggests that there is a substantial quantity of hydrogen on Titan. The atmosphere of Titan is a mystery. And if we go beyond the Saturnian system, we approach a region in the solar system about which we know almost nothing. Our feeble telescopes have not even reliably determined the periods of rotation of Uranus, Neptune and Pluto, much less the character of their clouds and atmospheres, and the nature of their satellite systems. The poet Diane Ackerman of Cornell University writes: “Neptune/is/elusive as a dappled horse in fog. Pulpy?/Belted? Vapory? Frost-bitten? What we know/wouldn’t/fill/a lemur’s fist.”

One of the most tantalizing issues that we are just beginning to approach seriously is the question of organic chemistry and biology elsewhere in the solar system. The Martian environment is by no means so hostile as to exclude life, nor do we know enough about the origin and evolution of life to guarantee its presence there or anywhere else. The question of organisms both large and small on Mars is entirely open, even after the Viking missions.

The hydrogen-rich atmospheres of places such as Jupiter, Saturn, Uranus and Titan are in significant respects similar to the atmosphere of the early Earth at the time of the origin of life. From laboratory simulation experiments we know that organic molecules are produced in high yield under such conditions. In the atmospheres of Jupiter and Saturn the molecules will be convected to pyrolytic depths. But even there the
steady-state concentration of organic molecules can be significant. In all simulation experiments the application of energy to such atmospheres produces a brownish polymeric material, which in many significant respects resembles the brownish coloring material in their clouds. Titan may be completely covered with a brownish, organic material. It is possible that the next few years will witness major and unexpected discoveries in the infant science of exobiology.

The principal means for the continued exploration of the solar system over the next decade or two will surely be unmanned planetary missions. Scientific space vehicles have now been launched successfully to all the planets known to the ancients. There is a range of unapproved proposed missions that have been studied in some detail. (See
Chapter 16
.) If most of these missions are actually implemented, it is clear that the present age of planetary exploration will continue brilliantly. But it is by no means clear that these splendid voyages of discovery will be continued, at least by the United States. Only one major planetary mission, the Galileo project to Jupiter, has been approved in the last seven years—and even it is in jeopardy.

Even a preliminary reconnaissance of the entire solar system out to Pluto and a more detailed exploration of a few planets by, for example, Mars rovers and Jupiter entry probes will not solve the fundamental problem of solar system origins; what we need is the discovery of other solar systems. Advances in ground-based and spaceborne techniques in the next two decades might be capable of detecting dozens of planetary systems orbiting nearby single stars. Recent observational studies of multiple-star systems by Helmut Abt and Saul Levy, both of Kitt Peak National Observatory, suggest that as many as one-third of the stars in the sky may have planetary companions. We do not know whether such other planetary systems will be like ours or built on very different principles.

We have entered, almost without noticing, an age of exploration and discovery unparalleled since the Renaissance. It seems to me that the practical benefits of
comparative planetology for Earthbound sciences; the sense of adventure imparted by the exploration of other worlds to a society that has almost lost the opportunity for adventure; the philosophical implications of the search for a cosmic perspective—these are what will in the long run mark our time. Centuries hence, when our very real political and social problems may be as remote as the very real problems of the War of the Austrian Succession seem to us, our time may be remembered chiefly for one fact: this was the age when the inhabitants of the Earth first made contact with the cosmos around them.

THERE IS ON
the Moon a small impact crater called Galilei. It is about 9 miles across, roughly the size of the Elizabeth, New Jersey, greater metropolitan area, and is so small that a fair-sized telescope is required to see it at all. Near the center of that side of the Moon which is perpetually turned toward the Earth is a splendid ancient battered ruin of a crater, 115 miles across, called Ptolemaeus; it is easily seen with an inexpensive set of field glasses and can even be made out, by persons of keen eyesight, with the naked eye.

Ptolemy (second century
A.D.
) was the principal advocate of the view that our planet is immovable and at the center of the universe; he imagined that the Sun and the planets circled the Earth once daily, imbedded in swift crystalline spheres. Galileo (1564–1642), on the other hand, was a leading supporter of the Copernican view that it is the Sun which is at the center of the solar system and that the Earth is one of many planets revolving around it. Moreover, it was Galileo who, by observing the crescent phase of Venus, provided the first convincing observational evidence in favor of the Copernican view. It was Galileo who first called attention to the existence of craters on our natural satellite. Why, then, is crater Ptolemaeus so much more prominent on the Moon than crater Galileo?

The convention of naming lunar craters was established by Johannes Höwelcke, known by his Latinized name of Hevelius. A brewer and town politician in Danzig, Hevelius devoted a great deal of time to lunar cartography, publishing a famous book,
Selenographia
, in 1647. Having hand-etched the copper plates used for printing his maps of the telescopic appearance of the Moon, Hevelius was faced with the question of what to name the features depicted. Some proposed naming them after Biblical personages; others advocated philosophers and scientists. Hevelius felt that there was no logical connection between the features on the Moon and the patriarchs and prophets of thousands of years earlier, and he was also concerned that there might be substantial controversy about which philosophers and scientists—particularly if they were still alive—to honor. Taking a more prudent course, he named the prominent lunar mountains and valleys after comparable terrestrial features: as a result we have lunar Apennines, Pyrenees, Caucasus, Juras and Atlas mountains and even an Alpine valley. These names are still in use.

Galileo’s impression was that the dark, flat areas on the moon were seas, real watery oceans, and that the bright and rougher regions densely studded with craters were continents. These maria (Latin for “seas”) were named primarily after states of mind or conditions of
nature: Mare Frigoris (the Sea of Cold), Lacus Somniorum (the Lake of Dreams), Mare Crisium (the Sea of Crises), Sinus Iridum (the Bay of Rainbows), Mare Serenitatis (the Sea of Serenity), Oceanus Procellarum (the Ocean of Storms), Mare Nubium (the Sea of Clouds), Mare Fecunditatis (the Sea of Fertility), Sinus Aestuum (the Bay of Billows), Mare Imbrium (the Sea of Rains) and Mare Tranquillitatis (the Sea of Tranquillity)—a poetic and evocative collection of place names, particularly for so inhospitable an environment as the Moon. Unfortunately, the lunar maria are bone-dry, and samples returned from them by the U.S. Apollo and Soviet Luna missions imply that never in their past were they filled with water. There never were seas, bays, lakes or rainbows on the Moon. These names have survived to the present. The first spacecraft to return data from the surface of the Moon, Luna 2, touched down in Mare Imbrium; and the first human beings to make landfall on our natural satellite, the astronauts of Apollo 11, did so, ten years later, in Mare Tranquillitatis. I think Galileo would have been surprised and pleased.

Despite Hevelius’ misgivings, the lunar craters were named after scientists and philosophers by Giovanni Battista Riccioli in a 1651 publication,
Almagestum Novum.
The title of the book means “The New Almagest,” the old Almagest having been the life’s work of Ptolemy. (“Almagest,” a modest title, means “The Greatest” in Arabic.) Riccioli simply published a map on which he placed his personal preferences for crater names, and the precedent and many of his choices have been followed without question ever since. Riccioli’s book came out nine years after the death of Galileo, and there has certainly been adequate opportunity to rename craters later. Nevertheless, astronomers have retained this embarrassingly ungenerous recognition of Galileo. Twice as large as crater Galileo is one called Hell after the Jesuit father Maximilian Hell.

One of the most striking of the lunar craters is Clavius, 142 miles in diameter and the site of a fictional lunar base in the movie
2001: A Space Odyssey.
Clavius
is the Latinized name of Christoffel Schlüssel (= “key” in German = Clavius), another member of the Jesuit order, and a supporter of Ptolemy. Galileo engaged in a protracted controversy on the priority of discovery and the nature of sunspots with yet another Jesuit priest, Christopher Scheiner, which developed into a bitter personal antagonism and which is thought by many historians of science to have contributed to the house arrest of Galileo, the proscription of his books, and his confession, extracted under threat of torture by the Inquisition, that his previous Copernican writings were heretical and that Earth did not move. Scheiner is commemorated by a lunar crater 70 miles across. And Hevelius, who objected altogether to the naming of lunar features after people, has a handsome crater named after himself.

Riccioli gave the names Tycho, Kepler and, interestingly, Copernicus to three of the most prominent craters on the Moon. Riccioli himself and his student Grimaldi received large craters at the limb, or edge, of the moon, Riccioli’s being 106 miles across. Another prominent crater is named Alphonsus after Alphonso X of Castile, a thirteenth-century Spanish monarch who had commented, after witnessing the complexity of the Ptolemaic system, that had he been present at the Creation, he could have given God some useful suggestions on ordering the universe. (It is amusing to imagine Alphonso X’s response were he to learn that seven hundred years later a nation across the Western ocean would send an engine called Ranger 9 to the Moon, automatically producing images of the lunar surface as it descended, until finally it crashed in a pre-existing depression named, after His Castilian Majesty, Alphonsus.) A somewhat less prominent crater is named after Fabricius, the Latinized name of David Goldschmidt, who in 1596 discovered that the star Mira varied periodically in brightness, striking another blow against the view championed by Aristotle and supported by the Church that the heavens were unchanging.