Early morning on Sunday, Sept. 24, the OSIRIS-REx spacecraft's sample capsule will come face-to-face with Earth's atmosphere for the first time since the mission's 2016 launch. On board are an estimated 8.8 ounces, or 250 grams, of rocky material collected from the surface of Bennu in 2020—NASA's first asteroid sample and the largest ever collected in space.

When it approaches Earth, the OSIRIS-REx spacecraft won't slow down as it makes its sample drop-off. Instead, when it reaches 63,000 miles (or 102,000 kilometers) above Earth's surface—about one-third the distance from Earth to the moon—a message from operators on the ground will trigger the capsule's release and the capsule will be sent spinning toward the atmosphere below.