Venus Express, for instance, has been seeking signs of active volcanism on the planet. "It's been looking for volcanically generated gases, volcanic plumes in the lower atmosphere," says Wilson, adding that the craft's findings have import beyond the present state of the cloudy, scorching planet. "We can start to understand the wider [question] of how Venus and Mars and the Earth evolved over their lifetimes. They were all created at the same time out of the same material, so how is it that these initially similar planets have evolved so differently?"
Unfortunately, sending another lander to Venus to build on the Venera tradition would be pricey. "The main concept that's been on the drawing table for a long-lived lander is you have to take an air conditioner to keep your electronics cool," Wilson says. "And you don't have all that much sunlight, so then you take a nuclear power source to run your cooler." A cheaper way to answer some big questions, he says, would be to deploy a balloon in Venus's clouds, as was done during the Vega missions of the 1980s. At the right altitude temperatures would be a balmy 20 degrees Celsius. "Not too hot, not too cold, and atmospheric pressure of half of one Earth atmosphere." A hypothetical astronaut, Wilson ventures, "could probably get away without even wearing a pressure suit. It's comfortable—except you're surrounded by poisonous sulfuric clouds."
Studying the surface from a perch in the clouds would be challenging, Wilson acknowledges, but a balloon mission could at least investigate how Venus's cloud chemistry works and taste the atmosphere to directly determine its composition. Perhaps by the next transit of Venus, in 2117, planetary scientists will have the answers to these questions and more.