Enlarge / An Electron rocket launches in August 2019 from New Zealand. (credit: Sam Toms/Rocket Lab) At the beginning of this year, a group of NASA scientists agonized over which robotic missions they should choose to explore our Solar System. Researchers from around the United States had submitted more than 20 intriguing ideas, such as whizzing by asteroids, diving into lava tubes on the Moon, and hovering in the Venusian atmosphere. Ultimately, NASA selected four of these Discovery-class missions for further study.