Overview | 101955 Bennu – Solar System Exploration: NASA Science

During the mission’s approach phase, between mid-August and early December, the spacecraft traveled 1.4 million miles (2.2 million km) on its journey from Earth to arrive at a location 12 miles (19 km) from Bennu on Dec. 3. During this time, the science team on Earth aimed three of the spacecraft’s instruments towards Bennu and began making the mission’s first scientific observations of the asteroid. OSIRIS-REx is NASA’s first asteroid sample return mission.

Data obtained from the spacecraft’s two spectrometers, the OSIRIS-REx Visible and Infrared Spectrometer (OVIRS) and the OSIRIS-REx Thermal Emission Spectrometer (OTES), reveal the presence of molecules that contain oxygen and hydrogen atoms bonded together, known as “hydroxyls.” The team suspects that these hydroxyl groups exist globally across the asteroid in water-bearing clay minerals, meaning that at some point, Bennu’s rocky material interacted with water. While Bennu itself is too small to have ever hosted liquid water, the finding does indicate that liquid water was present at some time on Bennu’s parent body, a much larger asteroid.

An ancient relic of our solar system’s early days, Bennu has seen more than 4.5 billion years of history. Scientists think that within 10 million years of our solar system’s formation, Bennu’s present-day composition was already established. Bennu likely broke off from a much larger carbon-rich asteroid about 700 million to 2 billion years ago. It likely formed in the Main Asteroid Belt between Mars and Jupiter, and has drifted much closer to Earth since then. Because its materials are so old, Bennu may contain organic molecules similar to those that could have been involved with the start of life on Earth.

Ten Things to Know About 101995 Bennu

10 Things to Know About 101955 Bennu

Found in 1999

The asteroid was discovered by the Lincoln Near-Earth Asteroid Research (LINEAR) survey on September 11, 1999.

Named by 9-year-old

Bennu’s original designation was 1999 RQ36. In 2013, a third-grade student named Michael Puzio won a contest to name the asteroid.

Far from home

Bennu has drifted into near-Earth space because of gravitational interactions with giant planets and the gentle push of heating from the Sun.

Low density

Bennu's density is only about 30 percent more than water. This suggests the asteroid is probably a loose collection of rocks, like a pile of rubble.

Wave every 6 years

Bennu has a close approach to Earth every six years.

Potentially hazardous

Scientists estimate Bennu has a 1‐in‐2,700 chance of impacting the Earth during one of its close approaches to the Earth in the late 22nd century.

burn up or bolt?

Bennu may burn up in the Sun. Over millions of years, of all of the planets, Bennu is most likely to hit Venus

A lone boulder

As of 2018, Bennu seems to have a smooth shape, except for one boulder that’s 33 to 66 feet (10 to 20 meters) in diameter, visible in radar images.

Moonless

Although some asteroids have moons, Bennu does not.

More to come soon

NASA’s OSIRIS-REx mission will reveal Bennu in unprecedented detail. It will collect a sample and return it to Earth in 2023.

Did You Know?

The name Bennu comes from an Egyptian deity related to the Sun, often depicted as a gray heron. Michael Puzio, who came up with the name for the asteroid at age 9, said he chose it because he imagined that the OSIRIS-REx solar panels and sample-collecting arm look like Bennu’s neck and wings.

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