As an ancient, carbon-rich asteroid, Ryugu is thought to be a time capsule of solar system history. To read that history, Hayabusa2 explored Ryugu from June 2018 to November 2019, and grabbed two samples from the asteroid to bring back to Earth (SN: 7/11/19). Hayabusa2 observed how the asteroid’s surface retained and released heat, a clue to its composition and structure. Dense rocks take in heat slowly and hold that heat for longer; more porous rocks change temperature quickly, like sand on a beach. Ryugu’s heat map shows that it’s about 50 percent porous, meaning half of it is holes,...
