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Most pictures of the Venus surface are synthetic, like this view of a volcanic region called Eistla, created from Magellan orbital radar data. The SAGE lander would take actual photos from ground level. (NASA/JPL)

Forbidden Planet

We’ve been to the moon. Mars is easy. But landing on Venus? That’s tough.

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Over the past 15 years, astronomers have identified about 500 planets around distant stars, and are now closing in on the ultimate prize: finding a world similar to our own, with conditions right for life. Such a discovery would be a technological triumph and a historic scientific achievement.

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But we should never have had to look so far.

Venus—the planet closest to us, and our twin in terms of size and mass—should by rights have developed in parallel to Earth. Instead it became a monstrosity, the relative we hardly mention and rarely visit. In the planet’s dense atmosphere, carbon dioxide, a greenhouse gas, somehow built up to toxic levels, now accounting for 96.5 percent of Venus’ air, as compared to 0.04 percent of Earth’s. The runaway greenhouse effect made Venus hotter than a self-cleaning oven, with atmospheric pressures equivalent to those found half a mile under Earth’s oceans. Says space physicist Larry Esposito of the University of Colorado at Boulder, “Dante’s vision of hell is real, and it is the planet next door.”

Maybe that’s why he likes studying it. Esposito began his space science career with NASA’s Pioneer Venus missions in 1978, and in 1995 he was the first to observe the planet with the Hubble Space Telescope. Landing on Venus has proven a more elusive goal, though. No one has sent a probe to the surface in 25 years, and NASA has never even tried. Since the Magellan orbiter mapped Venus with radar in the early 1990s, the U.S. space agency has focused its attention primarily on Mars and the outer planets.

Meanwhile, Esposito has pitched Venus mission proposals to NASA and the space agencies in Europe, Russia, and Japan, with mixed success. His curiosity about the planet—“particularly the comparison between Venus, Earth, and Earth-like planets”—drove him on, he says, and he never lost interest. “I’ve been busily working on [concepts] for 30-some years. I’ve always had a plan for a future mission to Venus. Every year it changes.”

Esposito’s time may finally have arrived. As greenhouse gases like CO2 build up in Earth’s atmosphere, scientific priorities are shifting, and closer attention is being given to proposals to study a neighboring planet that may be an object lesson for Earth. Last December, NASA gave Esposito $3.3 million to further develop his Surface and Atmosphere Geochemical Explorer (SAGE) concept, which would place a small probe equipped with cameras, spectrometers, and other instruments on the Venusian surface. If NASA decides to fund SAGE (next year the agency will choose between it and two other proposed missions: one to an asteroid, the other to the moon), then a spacecraft could return to Venus by 2018, becoming the first to visit there since the Soviet Union’s Vega 2 in 1985.

In the 1970s and 1980s, the Soviets practically tried to colonize Venus, sending more than a dozen landers and orbiters. One, Venera 13, which landed on March 1, 1982, lasted 127 minutes before expiring. At the height of the program, tens of thousands of people were working on the Veneras, according to Viktor Kerzhanovich, a Venera veteran and now a planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. In true cold war style, he says, the Soviet Union added as many zeroes to the Venera budget as were necessary to beat the Americans.

Given their prior successes, it’s not surprising that Russians like Kerzhanovich are eager to go back to Venus: “When the opportunity comes, I hope to be part of an American mission,” he says.

THERE’S A COMMON PERCEPTION that the Soviet Venus probes were crushed by the sheer weight of the planet’s atmosphere. That’s (mostly) false. But the truth’s not much better. Venus is the most inhospitable world in the inner solar system, boiling hot and rife with airborne acids. Developing the technologies to withstand those conditions—even for one afternoon—will take years and cost hundreds of millions of dollars. From the first brush with Venus’ atmosphere, the lander will be fighting thermodynamics, and it will lose.

The proposed SAGE lander would look, from the outside, like a giant ball bearing. But it will behave more like an insect, one of those poor bugs that lies dormant for decades, then claws out of its cocoon, sticks out arms and antennae in a frenzy of activity—and croaks. At least cicadas get weeks to romp. A Venus lander gets hours.

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