101955 Bennu

Asteroid· orbits the Sun

Bennu is a small, dark, carbon-rich near-Earth asteroid — a loosely bound rubble pile sampled by NASA's OSIRIS-REx in 2020, whose material was returned to Earth in 2023.

Open in 3D viewSee 101955 Bennu in the live, interactive 3D map

Key facts

Radius

0.245 km

Distance from Sun

1.13 AU

Orbital period

436.4 days

Eccentricity

0.2037

Rotation

4.30 hours

Science

Physical

Mean radius: 0.245 km
Mass: 7.33 × 10¹⁰ kg · 0.000000000000998 Moon masses
Density: 1,189 kg/m³ · 1.2× water; Computed from mass and radius
Rotation period: 4.30 hours

Orbital

Semi-major axis: 1.13 AU; From catalogued orbital elements (MPC)
Eccentricity: 0.2037; From catalogued orbital elements (MPC)
Inclination: 6.03 °; From catalogued orbital elements (MPC)
Orbital period: 436.4 days; From catalogued orbital elements (MPC)
Perihelion: 0.897 AU; Computed from the orbital elements
Aphelion: 1.36 AU; Computed from the orbital elements
Mean orbital velocity: 28.1 km/s; Computed from the orbital elements

Discovery

Discovered: September 11, 1999
Discoverer: the LINEAR survey

Composition

Make-up: A B-type rubble pile of hydrated clay minerals, carbonates and organic molecules — primitive material from the early Solar System.

Radiation & temperature

Insolation: 0.789 S⊕ · 79% of the sunlight Earth receives; Computed from the distance to the Sun (inverse-square; Earth's sunlight = 1), before any atmosphere.
Geometric albedo: 0.04; Geometric albedo ≈ 0.044 — a very dark surface (OSIRIS-REx).
Equilibrium temperature: 259 K (-14 °C); Computed from albedo + distance from the Sun (airless black body); uses the geometric albedo as an estimate

Discovery & history

Discovered: September 11, 1999
By: the LINEAR survey
Method: Photographic plates
Name: The ancient Egyptian Bennu bird (linked to creation and rebirth) — chosen by a nine-year-old in a naming contest.

Bennu is a small, dark, carbon-rich near-Earth asteroid found in 1999. As a potentially hazardous object and a pristine relic of the early Solar System, it was chosen as the target of OSIRIS-REx, which collected a sample in 2020 and delivered it to Earth in 2023.