INTRODUCTION the Recent Discovery of Extra-Solar Planets Has Created A
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INTRODUCTION First, know that heaven and earth and the liquid fields, the moon’s bright sphere and Titan’s star, a spirit within sustains; in every limb mind moves the mass and mingles with the mighty frame.1 ―Virgil, Aeneid 6: 724−727 The recent discovery of extra-solar planets has created a wave of revolu- tionary changes in the earth and planetary sciences. In the wake of these changes, the boundaries between ‘earth scientist’ and ‘planetary scientist’ have been blurred by a surge of new studies that suggest their intersection. Yet blurred boundaries are nothing new to science. Astronomers may point to Johannes Kepler (1571–1630) as a pioneer of this interplanetary vision. In his Dream (1634), an imaginary voyage to the moon, Kepler applied his knowledge of natural philosophy to describe what life might look like on the lunar surface. By projecting the laws of perspective, Kepler also explained why a lunarian observer might reasonably conclude that the moon stood motionless at the center of the world. The analogy was clear. “Everyone declares that the motion of the heavenly bodies around the earth [is] evident to the eyes,” Kepler wrote, “but to the eyes of the lunar- ians, it is evident that our earth rotates while their moon is motionless.”2 To press the imagination further, Kepler suggested that some of the lunar beings who enjoyed this view roamed the moon nomadically, either on foot, by air, or “on boats, following the receding waters.”3 Known as an early form of science fiction, Kepler’s Dream prompts readers to marvel at the idea of alien beings crossing the lunar surface “in large hordes” and diving to “the far depths of the sea” to avoid the heat of the sun.4 At the heart of this imaginative tale, however, is a seri- ous attempt to understand the physical reality of a faraway body. Today, astronomers and marine biologists cross similar lines when they contem- plate life beneath the surface of Europa and Jupiter’s other icy satellites. This cognitive leap has been elaborated by Stephen Hawking, who claims 1 Virgil portrays this spirit as similar in nature to fire and the universal source of life. 2 JKGW, 11,2, 354.23–25. Cf. Rosen, 1967, p. 106. 3 JKGW, 11,2, 330.19–20. Cf. Rosen, 1967, p. 27. 4 JKGW, 11,2, 330.23–26. Cf. Rosen, 1967, p. 28. 2 introduction that life on the ocean floor could hold clues for alien ecosystems similar to our own.5 It has even been introduced to the general public by James Cameron in his documentary, “Aliens of the Deep,” where we encounter a new world of life inhabiting the volcanic vents. While Kepler could never have imagined such a world, he plumbed the analogical depths of the earth to similar effect. Thus, the biblical account of creation in the earth’s waters served to illuminate the origin of comets in the celestial ether. In the same way that “great whales” had been born in the sea, Kepler claimed, the ether gave rise to comets “in every corner” of the heavens.6 Kepler would later turn to human anatomy to explain the complemen- tary roles of the sun and the planets in the body of the cosmos. If the sun was “a sort of heart,” the earth was “the liver or spleen.”7 Kepler blurred disciplinary boundaries because he believed the stars were subject to change in some of the same ways as the sublunar sphere. “Copernicus granted the right of citizenship in the heavens to the earth,” he declared,8 and with it came a new way of knowing the world of mutability beyond the moon. How did Kepler account for change according to the heliocentric hypothesis? The answer reveals a forgotten feature of his world view and a critical part of the new cosmology. Kepler envisioned a world of change beyond the perennial motion of the planets. Comets and new stars cried out for explanation in his “far-reaching philosophy of the heavens.”9 The constant cycle of decay and renewal that he imagined beyond the earth echoed the ancient principle of perfection that involved continual change. According to Aristotle, God had “fulfilled the perfection of the universe by making coming-to-be [on earth] uninterrupted.”10 This constancy of cre- ation and corruption secured a state of perpetual being that allowed the world thus to participate in perfection. Kepler saw no reason to limit this principle to any part of his world picture. The new planetary status of the earth suggested the same form of physical explanation extending to the fixed stars. While Kepler continued to study closely the light conveyed by 5 In his television series, “Into the Universe,” Hawking suggests that underwater aliens on Europa “would probably swim in a similar way to our own ocean life, since liquid water is the same stuff everywhere.” 6 JKGW, 4, 59.1–10. Cf. Genesis 1: 20–22. 7 JKGW, 6, 416.31–32. 8 JKGW, 1, 246.23–24. 9 Westman, 2011, p. 317. 10 Martin, 2011, p. 42..