“Some of those answers lie on Earth, but some of them lie on Venus,” Dr. Wilson said.

EnVision will study those mysteries with a suite of advanced scientific instruments. Its radar systems will peer through Venus’s thick atmosphere, mapping both the surface and the rocky layers up to 3,300 feet below the surface. An array of spectrometers seeing in ultraviolet and infrared light will analyze the atmosphere’s chemical composition, and differentiate between types of rock on the ground. A radio science experiment will be able to use slight changes in the planet’s gravity to parse the layer cake structure of Venus’s geologic guts.

All of these instruments will help answer another major query. “Is Venus alive or dead, geologically?” Dr. Wilson said. Venus, a world dominated by volcanoes and eruptive graffiti, clearly had a geologically hyperactive past. Although most scientists suspect that Venus is still erupting today, the thick cloud cover has prevented confirmation of that idea, just as it had prevented the search for the telltale earth-shattering movement of faults.

By conducting surgical scientific surveys on specific parts of the planet, EnVision will be able to comprehensively clear away this uncertainty. It can detect the thermal signatures of active volcanoes, sniff out the gaseous plumes from any erupting volcanoes and look for evidence of ongoing tectonic to-and-froing.

The spacecraft will also be able to peer into Venus’s past, looking for the scar tissue left behind by ancient plate tectonics and the relics of its epic, primordial volcanic activity — the sort that some suspect may have triggered the runaway greenhouse effect that dried up the planet. It will also investigate the tesserae, curious plateaus that rise above plains of younger lava. Some think these may turn out to be deformed layers of continent-like rock. If so, that means they formed in the presence of liquid water — yet more evidence that Venus was once an ocean world.

As capable as these three missions are, they won’t solve all of Venus’s mysteries, like whether phosphine, a gas potentially present in the planet’s clouds, is being manufactured by microbial life.

But the hope is that this is the beginning of a second Venusian renaissance. “It’s setting the stage for sustained Venus exploration,” Dr. Byrne said, and only a prolonged series of missions to Venus — from more orbiters and probes to atmospheric balloons and landers — will let us discover why it became Earth’s evil twin.