Venus, Near Neighbor of the Sun
Asimov traces cosmic sleuthing from ancient beliefs to modern knowledge, revealing the surprising, harsh realities of Venus, Mercury, and objects near the Sun.
The story begins, as many great human tales do, with the stars, those shining diamonds set against the velvet dark. Yet, among the fixed points of light, there were wanderers, or planetes. None commanded attention quite like the most brilliant of these wanderers, an object known in antiquity by two distinct names: the Evening Star, Hesperos, and the Morning Star, Phosphoros. For a long time, these were considered separate entities, beautiful twin celestial bodies taking turns in the sky. But careful, persistent observation, stretching back possibly to the Sumerians, revealed a profound truth that launched the central intellectual narrative of this account: Hesperos and Phosphoros were one and the same planet, orbiting the Sun in such a way that it could never stray too far from our great central star. The ancient Romans wisely named this singular, dazzling object Venus, after their goddess of love and beauty.
The initial stages of the story, then, concern establishing this planet’s true context within the cosmos. The introduction of the telescope by Galileo brought a pivotal turning point, much like the arrival of a crucial witness in a complex legal case. Galileo’s discovery that Venus exhibited phases, much like our own Moon, dealt a “final blow” to the older, Earth-centered models of the universe. This confirmed, logically and irrevocably, the Copernican view: Venus, Earth, and all the visible planets revolved about the Sun. The simple and elegant motions observed—the changes in phase and the enormous, corresponding shifts in apparent size as Venus moved from its nearest point (inferior conjunction) to its farthest (superior conjunction)—supported this new celestial framework perfectly. Venus, therefore, was not merely a shining object; it was Earth’s nearest, great neighbor.
However, the main plot of the story is the long, arduous struggle to peel back the layers of the planet itself, a mystery concealed by nature’s own defense mechanism. The brilliance of Venus, far outshining even the brightest stars and the next brightest planet, Jupiter, was itself a clue. It was due to an unbroken layer of cloud that never lifted, reflecting an immense fraction of the incoming sunlight, giving Venus an extraordinary albedo. This dense, perpetual veil ensured that for centuries, the planet’s true nature remained agonizingly obscure.
The story enters a speculative phase, reminiscent of the best scientific brainstorming. Since Venus was roughly Earth’s size, density, and chemical makeup, resembling a ‘twin sister,’ the popular expectation arose that beneath those bright clouds lay a world of mild, tropical warmth, perhaps a world of marshes or even an unbroken planetary ocean. Indeed, one might imagine it to be a younger version of Earth, where life was still developing, a view reinforced by earlier, though later superseded, theories of solar system formation. This hopeful narrative of a wet, temperate Venus was deeply ingrained in the popular imagination.
But science, unlike fiction, demands evidence. The cosmic sleuthing continued. The first counter-clue arrived through spectroscopic analysis, which confirmed the presence of large quantities of carbon dioxide in the atmosphere. Carbon dioxide, if present densely enough, could create a powerful warming trend, the so-called “greenhouse effect”. This dramatically changed the internal theory of the plot: if the greenhouse effect was runaway, that temperate ocean could have long ago boiled away, leaving Venus not a paradise, but a world of oppressive heat. This intellectual conflict between the traditional ‘wet’ Venus and the emerging ‘hot, dry’ Venus became the central tension of the story’s second half.
The climax of this grand narrative arrived with the advent of the Space Age. Unmanned probes, employing long-wavelength microwave radiation that could penetrate the thick cloud layer to measure the surface directly, finally resolved the centuries-old puzzle. The new knowledge revealed that the reality was far more extreme than most had dared imagine, characterized by hellish temperatures and crushing atmospheric pressure.
But the revelations did not stop there. The "story" of Venus concludes with further, strange complexities. Radar reflections used for accurate astronomical measurement simultaneously determined that Venus had an incredibly slow rotation period—longer even than its period of revolution around the Sun—and, stranger still, rotated in the retrograde (backward) direction. This unique state, combined with the lack of a detectable magnetic field, cemented Venus’s status as a world radically different from its twin, Earth. The narrative then broadens its scope, showing how the investigative techniques perfected on Venus were turned to its neighbor, Mercury, revealing that tiny planet's own surprising, yet related, rotational oddities.
The enduring strength of this intellectual journey is its absolute clarity and logical flow. It excels as a review of human progress, demonstrating how centuries of increasingly precise observation—from the geometry of celestial motion to modern radar pulses piercing clouds—systematically dismantled comforting myths about our closest planetary neighbor. The scientific process outlined here, akin to Asimov's own masterful storytelling, prioritizes truth above expectation, leading the reader from the mystery of the “Evening Star” to the unexpected reality of a hostile world, all while reinforcing the powerful, logical tools developed by humanity to understand its home in the solar system. The ultimate message is clear: even as one planetary mystery is solved, the findings spawn new, deeper questions about the origin and fate of planetary systems, hinting at the necessity of continuing space exploration.
