Bennu

A spacecraft went to Bennu to grab a handful of it, and nearly sank in — the surface turned out to be loose rubble, not solid rock! The whole asteroid is about as wide as a tall building is high.

🚀 Travel there

What it is

Rubble-pile near-Earth asteroid sampled by OSIRIS-REx; surface acted like loose fluff.

Asteroid: Rock or metal left over from building the planets. Every kind of thing there is →

Can you see it?

No. No telescope on Earth will show you this one; it is here to be understood, not seen. It is here because it is worth knowing about — and because leaving it out would make the sky look emptier than it is.

Worth knowing about Bennu

Bennu is about as wide as five football pitches laid end to end. In weight, about the mass of 13 Great Pyramids of Giza stacked together. A little farther out than Earth on average — a 'near-Earth asteroid'. Sunlight takes 9 minutes to reach Bennu — on average, because that distance changes as it goes round. Its year: just a little longer than one Earth year. Its day: 4.3 hours.

Its surface: 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.
What makes it worth knowing: Gravity is so weak — about 1/80,000th of Earth's — that you couldn't 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.

How did anyone measure the Earth in the first place?

The numbers

Across	0 km
Distance from the Sun, on average	1.13 AU ~169 million km · sunlight takes 9 minutes
Once round its orbit	1.2 Earth years
One day there	4.3 hours

What it belongs to

☀️ Everything the Sun holds, in one place 📖 How the solar system fits together

Then go outside

Not this one. But the sky over your head is full of ones you can see, and the Planetarium knows which.

🌙 Plan an evening outside 🌌 Everything else in the sky