A silent spacecraft carrying a microchip with more than 360,000 names is still circling an icy dwarf planet today. To get there, it did something long considered impossible: enter orbit around one world, map it for a year, then break away and orbit another. This deep dive covers NASA’s Dawn mission, launched in 2007 after repeated cancellations that were reversed only when Orbital Sciences offered to finish building it at cost.

The episode explains the xenon ion propulsion that produced thrust equal to a sheet of paper yet ran for 5.9 years and delivered 11.5 kilometers per second of velocity change. It then explores Vesta, a differentiated protoplanet with an iron-nickel core melted by aluminum-26 and the source of about 5 percent of meteorites found on Earth, and Ceres, a water-rich world whose bright spots in Occator Crater turned out to be sodium carbonate salts pointing to a briny subsurface ocean, ammonia antifreeze, cryovolcanism and organic molecules.

• Why Jupiter’s gravity left Vesta and Ceres as frozen building blocks of the early solar system
• The grain-of-sand analogy for ion thrust and why four days to reach 60 mph still wins in a vacuum
• HED meteorites and the Rheasilvia basin impact that scattered Vesta across the inner solar system
• How JPL engineers rewrote the flight software to steer with two reaction wheels and puffs of hydrazine after a cosmic ray hit
• The October 31, 2018 end of mission and the planetary protection orbit that keeps Dawn off the surface of Ceres