When NASA announced it would spend $1 billion developing two new missions to Venus—the agency's first visits in decades to Earth's hothouse twin—planetary scientists were elated, and not just because a long wait had ended. A dramatic shift in thinking about the planet over the past few years has made a visit even more enticing. Venus was once thought to have boiled off all its water almost as soon as it was born 4.5 billion years ago, turning into the parched, hostile world of today. But recent climate modeling has now suggested the planet's slow rotation would allow planet-spanning cloud decks to form, reflecting the Sun's attack and allowing Venus to host expansive oceans for billions of years—a nearly perfect setting for life. The two spacecraft, both selected as part of NASA's Discovery line of competed missions, will arrive later this decade, scouring the surface and atmosphere for signs of past water and plate tectonics—and clues to why Venus ultimately declined into an inferno.

当 NASA 宣布将斥资 10 亿美元开发两项新的金星任务——该机构几十年来首次访问地球的温室双胞胎——行星科学家们兴高采烈，不仅仅是因为漫长的等待已经结束。过去几年，人们对地球的看法发生了巨大转变，这让这次访问变得更加诱人。人们曾一度认为，金星几乎在 45 亿年前诞生之时就已经蒸发掉了所有的水，变成了今天炎热、充满敌意的世界。但最近的气候模型现在表明，这颗行星的缓慢自转将允许形成跨越行星的云层，反映太阳的攻击，并允许金星在数十亿年内拥有广阔的海洋——这是一个近乎完美的生命环境。这两艘航天器均被选为 NASA 发现系列竞争任务的一部分，