ANOTHER STAMP has just been added to the album of objects in the solar system visited by space probes. Bennu, pictured, is an asteroid that orbits the sun at approximately the same distance as Earth. This proximity, plus spectral analysis of its chemical composition (carbon-rich), radar analysis of its surface (smooth) and telescopic analysis of its spin rate (slow), made it the target of choice for a sample-return mission. That mission, OSIRIS-Rex, arrived on December 3rd. After an extensive inspection from an altitude of a few kilometres, OSIRIS-Rex will, in July 2020, swoop down and grab about 60 grams of material from the surface. It will leave Bennu in March 2021 and deliver the sample to Earth, in a special landing capsule, in September 2023.