ObserveTheSky › Everything in the sky › Bennu
asteroid · near-Earth asteroid (C-type, carbon-rich)

Bennu compared to Earth

Rubble-pile near-Earth asteroid sampled by OSIRIS-REx; surface so loose that the sampler sank straight into it.

Can you see it?

No small telescope will show you this one; it is here to be understood, not spotted.

How big is Bennu compared to Mount Etna?

Bennu is roughly 1/72 as wide as Mount Etna.

How far away is Bennu from the Sun compared to Earth?

Bennu orbits on average about one and a quarter times as far from the Sun as Earth does.

How long is a year on Bennu compared to Earth?

Bennu takes about 14 months to go once round the Sun.

How long is a day on Bennu compared to Earth?

Bennu turns round once in about 4.3 hours; Earth takes about 24 hours. And Bennu spins backwards.

Worth knowing about Bennu

Why it stands out
Gravity is so weak — less than a hundred-thousandth of Earth’s — that you could not really walk, only drift and gently push off. When OSIRIS-REx touched down in 2020, its sampling arm actually sank right in, as if the ground were a pit of loose fluff rather than solid rock, and the spacecraft had to fire its thrusters immediately to back away. The 2023 returned sample contained carbon, nitrogen and organic compounds — some of the basic ingredients for life — plus salty mineral crusts suggesting Bennu’s parent body once had liquid water, maybe even a small ancient ocean.
Its geology
A loose “rubble pile” of rocks held together by gravity, not solid rock.
The machines we sent
NASA’s OSIRIS-REx sampled Bennu and returned material to Earth in 2023, the first US asteroid sample return.
A near-Earth asteroid
Its orbit stays close to Earth’s own — which is what makes it reachable enough to visit at all, and also why it is worth keeping track of. Bennu comes back past us every six years, and its path is charted centuries ahead.
Bennu — A model of its measured shape, seen from the Earth and lit by the Sun: not a photograph, and not what a telescope shows.
The numbers
Mean diameter489.4 m
Distance from the Sun1.126 AU on average, from 0.897 to 1.356 AU · sunlight takes 9 minutes 22 seconds at its average distance
Once round its orbit1.195 Earth years
Sunrise to sunrise4.294 hours — and it turns the other way, so the Sun there rises in the west

How anyone knows this

Games it appears in

Show Bennu in the model☀️ Everything the Sun holds🌙 Plan an evening outside