Ellen Stofan, who two weeks ago stepped down as the chief scientist of NASA, says that the study of exoplanets brings Venus into the life-oriented NASA mission. “We’re in [a] phase of looking at these extrasolar planets and saying: Now wait a minute—Venus has something really important to tell us about why the Earth is habitable and why is Venus not.”

Early in Venus’s history, she explains, that planet had an ocean on its surface. Did life evolve in that interval? Earth has been habitable for about 3.9 billion years. Mars was habitable for maybe 500 million years. Europa might be inhabited today. “This is the question we're really struggling with now,” says Stofan. “It's not just: Are you a potentially habitable planet, but: How long did that period of habitability last? Did life take hold? Did it persist?” Venus helps answer those questions.

“If you only focus on Mars, if you only focus on Europa, you're not going to understand this. We need a broader program,” she says.

NASA cannot afford to add another multi-billion-dollar mission to its portfolio. The Venus community has therefore focused on tight Discovery-class missions in the $450 million range. The odds were in their favor in the most recent Discovery selection process. Scores of concepts were narrowed down to a final five, and two of those finalists were Venus missions. When NASA announced that it would then fund two Discovery missions, well it just seemed like Venus was set to see our return. Worst case scenario, one Venus mission would get approved, but after 28 years of nothing, that would be enough.

When NASA announced the selection of the two missions to asteroids and zero missions to Venus. Stofan, a Venus scientist who had recused herself from the process, says she was honestly surprised by the results, though describes the asteroid missions as “really great” with excellent principal investigators. She worries going forward is that NASA will soon find itself devoid of anyone with expertise in Venus missions, and the world with no one who has ever actually operated on the Venusian surface. “My huge concern is that the expertise is still there but it's going away. If we have no Venus missions it will definitely be gone. We will have lost something. We will have lost this capability and it's really unfortunate.”

Planetary exploration is a perishable skill at an institutional level. NASA is good at landing spacecraft on Mars because its engineers have been doing it for a long time. The engineering spoils of success, the lessons learned from failures, and the “We didn’t do that last time because…” conversations over coffee and in meetings are as important to exploration capabilities as saved AutoCAD drawings.

In the case of Venus, the chief problem facing engineers is the planet’s merciless thermal environment. When Venus scientists formulate new landing mission proposals, they reach out to the people who worked on NASA’s Pioneer-Venus, which sent probes to the surface of Venus in 1978. They speak with the Russians who landed the Venera and Vega probes. They talk, in other words, with the people who’ve actually done the job. But veterans of the Venus surface are diminishing in number.