Forever playing second fiddle

Every 10 years, the planetary science community prioritizes all the questions they want to answer during the next decade, laying them out in a long report called the Decadal Survey.

There are three types of planetary missions: Flagship, New Frontiers, and Discovery. Flagship missions are planned at the agency level, while New Frontiers and Discovery missions are competitively selected. New Frontiers missions are cost-capped at around a billion dollars, and Discovery missions go for about a half-billion.

NASA hasn't been willing to spring for a Flagship mission to Venus since Magellan, but the past two Decadal Surveys, in 2003 and 2013, have listed Venus as a potential destination for a Discovery or New Frontiers-class mission.

Last year, when NASA picked its latest Discovery mission, there were five finalists. Two were Venus proposals, but the agency instead picked two asteroid missions called Lucy and Psyche. This stung not just Venus scientists, but others within the larger space science community.

"Plenty of my colleagues outside the Venus community were aghast when a Venus mission was not selected in the last Discovery round," Gilmore says. "I think there is a sense in the planetary community as a whole, not just the Venus community, that Venus is quite overdue."

The scientists behind both of the losing Venus missions have re-tooled their proposals for a larger, New Frontiers budget. But more money is no guarantee of success; the last winning New Frontiers mission, OSIRIS-REx, also beat out a Venus finalist. That losing Venus mission is also trying again, giving NASA a total of three Venus missions to choose from when it makes the next New Frontiers selection this month.

But why does Venus keep losing out in the first place?

One theory, says Van Kane, who writes about future planetary exploration missions, is that there's virtually no chance to find life on Venus.

"NASA's planetary program has an emphasis on the search for life or the conditions that could lead to life," he says. "That puts Venus missions in competition with every other mission that isn't focused on life. That's a long list."

I asked everyone I interviewed for this story why NASA keeps passing over Venus, and almost everyone responded with some variation of "because it's hard." But "hard" may not be the right word.

"No planetary mission is easy," says Gilmore. "One could robustly argue that it is easier to put something in orbit or on the surface of Venus (the latter the Soviets did in 1970) than it is to land on Europa or rove on Mars," she said.

A more accurate explanation might be that Venus hides its secrets better than other destinations, meaning missions to places like Mars tend to get more science bang for the buck.

Take, for instance, the context camera aboard the Mars Reconnaissance Orbiter, Kane says. That same camera could conduct relatively inexpensive, global composition mapping of Venus—except that it wouldn't work there, because Venus's atmosphere makes that approach useless.

Similarly, a short-lived Venus lander only able to analyze its immediate vicinity might actually cost the same as a clone of the Mars Opportunity rover. But we can't send Opportunity to Venus because of the planet's hellish environment.