Some Breakthrough Discuss sessions felt almost like pitches, as scientists outlined compelling reasons to look for life at their destinations of choice. Carolyn Porco, who led the imaging science team for NASA's Cassini mission to Saturn, gave an overview of findings from the moon Enceladus. Enceladus has plumes that spray material from a subsurface ocean out into space; a lot of that material snows back down onto the moon's surface. The ocean has a salinity comparable to Earth, and Porco said "some of us now regard Enceladus as the most promising place in the solar system to search for life."

She wants to go back, preferably with a lander that would collect plume material falling back to the surface. If that's too ambitious, she suggests either an orbiter or slow flyby probe, so long as the spacecraft goes slow enough not to smush potential microorganisms like bugs on a car windshield. She believes any Enceladus mission should include a microscope that can capture images or video of potential life.

David Grinspoon, a senior scientist for the Planetary Science Institute, represented Team Venus, which lost out yet again this year in NASA's most recent competitively selected mission call. Venus may have once been habitable; current research puts liquid water on the surface about 2 billion years ago.

Grinspoon talked about the intriguing possibility that microbial life could exist in Venus's clouds. Before Grinspoon's talk, David Smith, an astrobiologist at NASA's Ames Research Center, talked about microbial matter that gets swept from Earth's surface up into the clouds. Smith is part of a team trying to figure out what those tiny lifeforms do up there: Do they propagate before fluttering back to Earth? Or are they ripped apart by ultraviolet radiation?

Smith's research is relevant because something similar could be happening at Venus. Since we don't expect to find life as we know it on Venus' surface, any cloud life there would have to be self-sustaining. Fortunately, unlike on Earth, there may be places in Venus's clouds where heat welling up from the surface keeps particles aloft indefinitely. More intriguingly, something in Venus' atmosphere is absorbing more than half the solar energy hitting the planet. Could it be a biological process? The idea has been floated—ha!—but Grinspoon warned there are other explanations, too. What we really need are some samples. Venus is underexplored," he said.

One of the destinations that beat out Venus in the above-mentioned mission selection round was Titan. Morgan Cable is part of the NASA team working on the proposed Dragonfly mission, which would explore Saturn's haze-covered moon using a dual-quadcopter that could fly hundreds of kilometers during a 2-year mission. Life as we know it needs three things, Cable said: energy, organics, and solvents (liquids, basically). Titan offers a two-for-one on solvents because it has methane lakes and a subsurface ocean.

The idea of sending a drone to Titan may seem far-out, but the dense air and low gravity there make flying easy. Even a human with makeshift wings might be able to fly on Titan. "I want to remind people that NASA dares mighty things," said Cable.