In the 1960s, intent on demonstrating the superiority of our military-industrial complex to the Soviet Union, we funded the space program to reach the moon. In the 1970s and 1980s, we began to justify space expenditures by touting Teflon pans, super metal alloys, and miniaturized ro-botics. Now a new rationale for planetary exploration has emerged-environmentalism. The more we know about other worlds, say space enthusiasts, the better we can tackle the environmental dilemmas that beset our own planet.

So argues planetary scientist David Harry Grinspoon of the University of Colorado at Boulder, in Venus Re-vealed: A New Look Below the Clouds of Our Mysterious Twin Planet, the first book to explain the findings of the Magellan mission. Expertly guiding the reader beneath the clouds that have long hidden Venus from earthbound eyes, Grinspoon celebrates Magellan and other spacecraft voyages that have increased our understanding of our sister planet’s geology, climate, and atmosphere. At the same time, he acknowledges that these insights may not play well with a taxpaying public facing declining schools, disintegrating inner cities, overpopulation, and many other social ills. So throughout the book, Grinspoon emphasizes how missions like Magellan may lead to practical solutions to problems here on earth, such as ozone depletion, global warming, and acid rain.

What’s striking about Venus Re-vealed, besides some captivating Magellan photos of the Venusian landscape, is the author’s informal style. It immediately comes across in the introduction, where he describes an exhilarating drive up California’s Pacific Coast Highway to catch views of Voyager 2’s Neptune encounter at the Jet Propulsion Laboratory in 1989. This journey sets the tone for the rest of the book, which Grinspoon delivers like a smart, irreverent travel companion on a long-awaited road trip.

And there’s no excuse to drift off. If Grinspoon thinks you may be losing it during a discussion of a complex topic such as the relative motion of planets, he will pull the car to the side of the road, and bring you up to speed with an ex-planation section en-titled “Who Cares?” or a sports an-alogy (on the solar system track, “Venus is a runner on the inside lane”). At other times, he’ll lighten the load with an amusing footnote or quirky subtitle.

Taking the reader on a fascinating historical tour of Venus as seen from the imagination, telescopes, and spacecraft, the author gradually brings the planet into focus. Before the invention of the telescope, stargazers noticed how Venus stood out in the night sky. It was not only the brightest object, but also a quixotic companion to the sun, putting in rotating nine-month appearances as evening or morning star. The eye-catching planet inspired reverence in many ancient cultures, becoming a symbol of birth, death, and resurrection, a beacon of fertility (with its appearances matching the human gestation period), and a goddess of love.

Starting in the 1600s, astronomers viewed Venus through the telescope, initially discovering its moonlike phases, and later detecting an atmosphere, leading to speculation that Venus was a “swamp world,” with oceans, vegetation, and rain. But swathed in a global blanket of clouds, Venus refused to reveal its secrets through optical telescopes. To penetrate the cloud cover, twentieth century scientists turned to other instruments, such as ultraviolet detectors and radar.

From 1962 to 1994, an armada of 24 Soviet and American spacecraft missions radically altered our view of Venus. Their observations revealed a dimly lit planet largely devoid of water, with a 900 degrees Fah-renheit surface temperature, a 97 percent carbon dioxide atmosphere, and sulfuric acid clouds. By 1990, topographic maps, which were produced by radar pulses, and ground-based radar images yielded a fuzzy, incomplete picture of the surface.

Then came Magellan. Launched in 1989 and operating until 1994, Magellan “more than all the other spacecraft combined,” transformed Venus into a place, writes Grinspoon. The orbiter, carrying an onboard radio telescope that could resolve surface features as small as a football field, generated the radar equivalent of an Above Venus photo book.

According to an effusive Grinspoon, “It was like finally, after decades of squinting, getting the right prescription for your glasses and seeing the world in focus.” What Magellan “saw” was a well-preserved assortment of volcanic features (including pancake domes, meandering “river beds” apparently carved out by molten fluid, and basalt plains), tectonic scars (folds, fractures, and faults), prominent highlands, and highly reflective mountaintops. The surface, averaging only 500-600 million years old (“What’s a hundred million years among friends?” quips Grinspoon in a footnote), displayed only about 900 craters, prompting scientific speculation that a catastrophic event induced a “planetary makeover” about half a billion years ago.

In Grinspoon’s view, the findings of Magellan and other spacecraft have shown Venus to be our planet’s “fraternal twin.” While differing severely in many characteristics, Venus closely matches earth in others-size, mass, and distance from the sun, a geologically active and volcanic surface and an evolving atmosphere with complex chemical cycles.

Indeed, Venus’s atmosphere and clouds display processes with strong analogies to environmental problems on earth, compelling Grinspoon to include a section entitled “A Case of Venus Envy?” The atmosphere contains greenhouse gases (principally carbon dioxide), which trap heat beneath the clouds, globally warming the planet’s surface in a process similar to what happens on earth. Atop Venus’s clouds, ultraviolet light rips apart fluorine and chlorine compounds, yielding chemical compounds that deplete ozone-a discovery that contributed to scientists’ investigations of a similar phenomenon on our planet. And Venus’s sulfur dioxide clouds produce acid rain, a form of precipitation that continues to threaten earth’s lakes and forests.

These similarities-especially the green-house effect-have led many scientists to support missions to Venus, touting our sister planet as a model of what earth might become unless we significantly reduce our fossil-fuel consumption. But Grinspoon convincingly argues that “the lesson we can learn from the Venusian climate is not Don’t let this happen to your planet,’ but rather Here is another nearby planet with a complex, evolving climate system; study it and you will achieve a more mature, less provincial understanding of planetary climate.’ And that could save our hides.”

While Grinspoon clearly supports robotic space exploration for curiosity’s sake (“Beauty and mystery are reason enough to explore”), and argues that the United States could fly five advanced geoscience and climatology missions to Venus for the $1 billion cost of a Stealth bomber, he stresses that such projects are “ultimately vital to maintaining and enhancing the planetary perspective that may save us from ourselves.” Grinspoon deftly shores up this argument by pointing out how Apollo photos of earth “forever changed the self-image of earth’s inhabitants, helping to awaken our latent planetary identity.” The first indication of this was the inaugural Earth Day (1970). Moreover, the Apollo mission led scientists to sound the alarm about the potential harm of chemical reactions associated with CFCs to earth’s ozone layer. After several scientific papers, research programs, and global conferences, international agreements were forged to phase out CFC use.

Despite these success stories, funding space exploration remains a gamble, since there’s never a guarantee that learning about the unknown will pay off in more than intellectual terms. Although Grinspoon makes an interesting case for the practical potential of Venus exploration in addressing earth’s environmental problems, he fails to adequately explore the relative cost-effectiveness of more direct approaches, such as targeted economic and technical programs. A case in point is NASA’s up-coming Mission to Planet Earth project, which aims to systematically study our planet with remote-sensing satellites.

In a final chapter about the possibility of life on Venus, Grinspoon’s literary journey begins to veer onto dirt roads. He speculates on prospects for finding or introducing life on Venus and the significant challenges of manned planetary missions. While these side trips are intriguing, they ultimately distract the reader from the book’s central theme-the excitement and practical value of planetary exploration.

On the whole, however, Grinspoon’s joyride to Venus and back is truly consciousness-expanding, transforming our nearest planetary neighbor into much more than a bright dot in the sky. If you read Venus Revealed inside, you may find it difficult to suppress the urge to lay it down, go outside, and catch a glimpse of our spellbinding celestial twin.