Modern Space Exploration: Asteroids and Comets

Scientists chose Bennu as the target of the OSIRIS-REx mission because of its composition, size, and proximity to Earth. Bennu is a rare B-type asteroid (primitive and carbon-rich), which is expected to have organic compounds and water-bearing minerals like clays.

OSIRIS-REx traveled to near-Earth asteroid Bennu and is bringing a small sample back to Earth for study. The mission launched Sept. 8, 2016, from Cape Canaveral Air Force Station. The spacecraft reached Bennu in 2018 and will return a sample to Earth in 2023.

The OSIRIS-REx spacecraft is traveling to Bennu, a carbonaceous asteroid whose regolith may record the earliest history of our solar system. Bennu may contain the molecular precursors to the origin of life and the Earth’s oceans. Bennu is also one of the most potentially hazardous asteroids, as it has a relatively high probability of impacting the Earth late in the 22nd century.

One of the most intriguing targets in the main asteroid belt, 16 Psyche is a giant metal asteroid, about three times farther away from the Sun than is the Earth. Its average diameter is about 140 miles (226 kilometers) – about one-sixteenth the diameter of Earth’s Moon or about the distance between Los Angeles and San Diego. Unlike most other asteroids that are rocky or icy bodies, scientists think the M-type (metallic) asteroid 16 Psyche is comprised mostly of metallic iron and nickel similar to Earth’s core.

Space.com - 4/18/2021