The Case for Mars (6 page)

This insight was a shock to the medieval mind, but why was it necessary to kill to try to stop it? Why was Bruno’s younger contemporary Galileo threatened with death and then held under house arrest for decades? Why was astronomy, a science which concerns matters of apparently little practical value, such a torturous subject during the Renaissance? Why, in short, were the stakes so high?

The stakes were so very high because the science of astronomy placed the entire intellectual framework of Western civilization, of knowledge and therefore power, at risk. From the time of Babylon through Bruno’s day, the heavens, with their innumerable stars and five wandering planets, were considered divine and unknowable by all save a select few: astrologers and priests in Babylonian times, the Church in Bruno’s times. Listen to the second century
A.D
. librarian of Alexandria Claudius Ptolemy as he defended an astronomy that placed Earth at the center of the universe with the Sun and five known planets traveling along “epicycles,” small circular orbits whose centers move at a constant rate along the path of a greater circle centered around the Earth. Answering objections to the irrational nature of the epicycle scheme (additional epicycles were continually being added to the model to make it match observation), Ptolemy replied, “It is impermissible to consider our human conditions equal to those of the immortal gods and to treat sacred things from the standpoint of others that are entirely dissimilar to them. . . . Thus we must form our judgment about celestial events not on the basis of occurrences on Earth, but rather on the basis of their own inner essence and the immutable course of all heavenly motions.” For Ptolemy, the laws of the heavens were completely different from those governing the Earth. The universe was unknowable, unchangeable, and uncontrollable by man. With the divine plan
something beyond comprehension, only a ruling priesthood, with its unique access to the mystical and supernatural, could tell the people what was right and what to do.

So it stood for centuries, until the time came when a few thinkers challenged the notion that the universe would forever lie beyond humanity’s intellectual grasp. The action started with the work of Nicholas Copernicus, who between 1510 and 1514 redeveloped a long-forgotten heliocentric (Sun-centered) theory of the universe first posited by the third century B
.C
. Greek thinker Aristarchus of Samos. Under the heliocentric system, the planets traveled about the Sun in circular orbits. This concept was revolutionary, heretical even, and could not precisely match the observed planetary motions, yet some scholars of the time saw beauty in the fundamental simplicity of Copernicus’ system. Chief among them was Johannes Kepler.

Born in 1571, Kepler grew to be a devout Lutheran, yet also a diehard Platonist with a passion for seeking the true nature of the universe in the rational laws of geometry. He would write, “Geometry is one and eternal, a reflection out of the mind of God. That mankind shares in it is one of the reasons to call man an image of God.”

This quote is the key to the whole affair. If the human mind can understand the universe, it means that the human mind is fundamentally of the same order as the divine mind. If the human mind is of the same order as the divine mind,then everything that appeared rational to God as he constructed the universe, its “geometry,” can also be made to appear rational to the human understanding, and so
if we search and think hard enough, we can find a rational explanation and underpinning for everything
. This is the fundamental proposition of science. It is this proposition that Bruno died for. It is this proposition that Kepler set out to prove, and by so doing, to lift the darkness off the soul of Western civilization. And that he did, with a significant piece of help from the planet Mars.

In February 1600, the same month as Bruno’s execution, Kepler went to work for Tycho Brahe, without question the greatest observational astronomer of his time. Brahe had his own theory of the universe, and entrusted the twenty-eight-year-old Kepler with the task of determining Mars’ orbit, all for the glory of Brahe’s own theories, of course. When Brahe died in October 1601, the Holy Roman Emperor Rudolph II ordered that Kepler be put in charge of the treasure trove of Brahe’s observati
ons and that he succeed Brahe as Imperial Mathematician. Kepler now had the ammunition needed to undertake his assault on Mars in earnest.

Since the time of Aristotle, astronomers had simply assumed that the planets moved in uniform circular orbits because, as Aristotle himself argued, the circle was a perfect form, and only circular motions could come back on themselves and ensure an eternal motion. Try as he might, though, Kepler simply could not get any sort of circular orbit to match Brahe’s observations. True, he could have invoked epicycles, but this Kepler refused to do. Ad-hoc systems of epicycles were irrational—and there had to be a rational answer. But if not circular orbits, what could it be? It took eight years of intense intellectual effort for Kepler to discover what Tycho’s observations of Mars revealed: Mars traveled in an elliptical orbit, with the Sun as one focus of the ellipse. We now know that Mars’ orbit is the most elliptical of all the planets, except Pluto, which was not discovered till the twentieth century, and therefore presented the acid test for any astronomical theory. Indeed, if Mars’ orbit had been circular, the Aristarchus/Copernicus theory would probably have passed muster without anyone looking much deeper.

Kepler published the results of his labors in 1609 in a work entitled, in full,
A New Astronomy Based on Causations or a Celestial Physics Derived from Investigations of the Motions of Mars Founded on the Observations of the Noble Tycho Brahe.
Unlike many previous astronomers and philosophers, Kepler declared that this new astronomy was not simply a mathematical construct that reproduced the motions of the heavens. It was, instead, a treatise on the “true reality” of the heavens, an epic work that overthrew two thousand years of dogma and replaced it with an astronomy based on causes. In it he laid out what are now known as Kepler’s first two Laws of Planetary Motion; that the planets move in elliptical orbits with the Sun at one focus, and that the radius vector from the Sun to the planet sweeps out equal areas in equal times. These laws are correct and are found today in all textbooks on astrodynamics. Equally important, however, was what strictly speaking can be called Kepler’s
incorrect
hypothesis: that the planets were pulled by a “magnetic” force emanating from the Sun, spreading out from it “in the manner of sunlight.” When his opponents accused him of mixing physics with astronomy, Kepler replied, “I believe that both sciences are so closely bound that
neither can achieve perfection without the other.” In other words, Kepler did not describe a model of the universe whose geometry was merely appealing— heas investigating a universe whose causal relationships could be understood in terms of nature knowable to man. In so doing, Kepler catapulted the status of humanity in the universe. Though no longer residing at the center of the cosmos, humanity, Kepler showed, could comprehend it. Therefore, as Kepler wrote to Galileo in the quote that leads this chapter, not only was the universe within man’s intellectual reach, it was, in principle, within physical reach as well.

Ten years of further study followed, until Kepler was able to publish his masterpiece,
The Harmony of the World.
Here he laid out his final great discovery, the Third Law of Planetary Motion; that the square of the periods of revolution of the planets is proportional to the cube of their distances from the Sun. Once you have this law, it is a relatively simple matter to derive mathematically what is now known as Newton’s Law of Universal Gravitation. Newton’s laws are the basis of what is known as classical physics, the powerful new body of scientific knowledge that made possible the Industrial Revolution in the eighteenth and nineteenth centuries. With Kepler’s study of the planet Mars, the Dark Ages came to an end, and the scientific and industrial revolutions began—humanity’s first encounter with Mars had paid off handsomely.

VOYAGES BY TELESCOPE

Kepler had used Mars to prove that the Earth was a planet. By implication, therefore, the planets, those little moving lights in the sky, were really vast worlds like the Earth. But how to explore these incredible new bodies? A tool was soon at hand. Barely a year after Kepler published his New
Astronomy
, Galileo turned a new instrument toward the heavens—a telescope. His discovery of mountains on the Moon and “three little stars” dancing about Jupiter over the course of several weeks of observing gave additional credence to the Keplerian view of the universe. Soon enough, other telescopes were trained on Mars.

The Italian astronomer Francisco Fontana produced in 1636 the first drawing of Mars through the telescope, though viewed today it reveals no recognizable fea
tures. In 1659 the Dutch astronomer Christiaan Huygens produced the first drawing that shows a known Martian feature, a roughly triangular dark blotch that appears on the planet’s face, today known as Syrtis Major. By carefully observing Syrtis and similar features, early astronomers determined that the Martian day, or sol, was close to Earth’s. In 1666, the Italian Giovanni Cassini measured the Martian day at 24 hours, 40 minutes, about two and one-half minutes longer than today’s accepted measure of 24 hours, 37 minutes, 22 seconds. Although Cassini was also apparently the first to note one of Mars’ polar caps, Huygens in 1672 produced the first sketch of one of the caps. Utilizing observations made between 1777 and 1783, William Herschel, discoverer of Uranus, noted that Mars should have seasons, as its polar axis was tilted about 30° (24° is the modern value) to its orbital plane.

Observations of Mars continued through the decades, especially around “oppositions,” those times when Mars (technically, any planet outside Earth’s orbit) lies on the opposite side of the Earth from the Sun. At these times, Mars is at its closest to Earth and thus shines most brightly in the sky. By the early nineteenth century, astronomers had collected a basketful of basic Mars statistics: its orbital period; the length of its day; the planet’s mass and density; distance from the Sun, and surface gravity. But what truly intrigued observers was the changing face of Mars. Through the years the telescope’s eyepiece revealed that Mars’ face was mottled with ar darkpatches that came and went with time. Likewise, the bright white spots observers noted at the poles appeared to vary with the Martian seasons, expanding and contracting over the course of a Martian year. And Mars apparently hosted an atmosphere, as some observers spied vague indications of clouds above the Martian surface.

The opposition of 1877 proved especially fruitful for observers and for Martian studies. Asaph Hall of the U.S. Naval Observatory discovered two small moons of Mars and promptly named them Phobos and Deimos—fear and terror, an appropriate entourage for the planet of war. But in hindsight, 1877 is perhaps best remembered for a series of observations that launched a turbulent episode in the history of Mars observations and one of the strangest chapters in the history of astronomy.

Among those who turned a telescopic eye toward Mars in 1877 was the Italian astronomer Giovanni Schiaparelli, director of the Brera Observatory in Milan. Sch
iaparelli’s reports of his observations noted the location of more than sixty features on the Martian surface. But, along with many standard features, he reported sighting linear markings crisscrossing the face of Mars. He named these features after terrestrial rivers—Indus, Ganges—but referred to them in his writings as “canali,” the Italian plural for channels or grooves. While not the first to note these strange markings, he was the first to identify an extensive system of “canali.” More than a decade later, the enthusiasms of Percival Lowell would catapult Mars and its “canali” to headline status throughout the world.

Born into an illustrious New England family of poets, educators, statesmen, and industrialists (the great poet Amy Lowell was his sister, his brother Abott was president of Harvard), Lowell while in his late thirties became intrigued with Mars, especially with Schiaparelli’s observations. For Lowell there could be only one interpretation—for “canali” Lowell read not channels, but canals. Canals reflect the work of minds in collaboration, of life. For reasons that remain unclear, Lowell decided that Mars demanded his attention and devote his attention to Mars he did, with a passion and pocketbook few could match.

The tool Lowell built for his investigations—the Lowell Observatory in Flagstaff, Arizona—saw first light in April 1894, just a few weeks before Mars reached its biennial opposition with Earth. Lowell and his staff atop Mars Hill spent more than a decade studying and mapping the face of Mars. Lowell and his assistants mapped hundreds of canals. In their number and organization, Percival Lowell saw the history of an alien race trying to survive on an arid, dying world plainly writ.

Lowell captured the popular imagination with his sympathetic picture of an intelligent race of Martians trying to forestall its inevitable doom. The effect of his writings was amplified further by adventure writers such as Edgar Rice Burroughs, who used the Lowellian Mars as the setting for an extraordinary romantic Martian civilization that called its home planet “Barsoom.” Burroughs’s Mars novels featured swashbuckling heroes rescuing daring and beautiful princesses endangered by monsters, savages, and power-mad Martian tyrants, all set against a rich tapestry of life on Barsoom. In its Barsoomian incarnation, Lowell’s Mars enchanted millions of readers.

Over the years though, ne
ither Lowell’s eloquence as a writer and speaker nor his energy and enthusiasm could defend his theories against the barbs of the astronomical community. The tide of opinion slowly turned against Lowell as other observers that remag more powerful telescopes found no evidence whatsoever of canals. We now know that Lowell was absolutely wrong in his investigations of Mars, but he did leave an important legacy behind: he fired the imaginations of people to make them see a world on Mars. True, that world turned out to be wildly inaccurate, but its envisionment led to a massive uplifting of at least a segment of the popular mind, which three centuries after Kepler was and still is largely addicted to the ancient geocentric view of the Earth as the only world, orbited by tiny lights in the sky. Lowell made Mars habitable in the imagination only, but it is from imagination that reality is created. It was Lowell’s works that inspired the pioneers of rocketry, including Robert Goddard and Herman Oberth, to begin their quest to develop the tools that would soon make the solar system accessible, not only to the eye, but to the hand of man. It was the spirit of Lowell that touched the rocky surface of Mars as
Viking
landed.