What Is Asteroid Bennu? One of the Most Hazardous Space Rocks We Know


NASA has given newly revised figures about the threat posed by the asteroid 101955 Bennu.

In a study released on Wednesday, NASA researchers said the chance of Bennu hitting Earth through the year 2300 is about 1 in 1,750. They also found that September 24, 2182, was “the most significant single date” for impact risk, with a probability of 1 in 2,700, according to the statement from the space agency.

Bennu has been the subject of scientific investigation for years, particularly since the OSIRIS-REx probe arrived at the vast space rock in December 2018.

NASA describes the asteroid as one of the two most hazardous in the solar system, even though the impact risk is still very low.

Impact threats aside, Bennu is of scientific importance for a number of reasons. For one thing, the asteroid’s average orbital distance from the sun is around 105 million miles, which is relatively close to that of the Earth at 93 million miles.

What’s more, it is a rare type of asteroid known as a B-type. That means it’s both very old—scientists think it formed over 4.5 billion years ago—and rich in carbon and might contain organic compounds.

On and beneath its pitch black surface, Bennu may contain chemicals and rocks from the birth of the solar system.

Plus, at 510 meters (1,673 feet) from pole to pole, Bennu is suitably large for an investigatory mission.

Sample From the Surface

For these reasons Bennu was selected as the target for OSIRIS-REx, and from late 2018 until earlier this year a probe had been circling the space rock to gather as much data as it could on its orbital path, size and shape, mass, composition and spin. Crucially, it also grabbed a surface sample.

The OSIRIS-REx probe began slowly drifting away from Bennu in April this year and set off on a two-year cruise back to Earth around a month later.

The probe is expected to return its Bennu surface sample, described by NASA as “pristine and precious cargo,” to Earth on September 24, 2023.

Bennu comes close to Earth once every six years, and orbits at an average speed of around 63,000 miles per hour. It takes about 1.2 years to fully orbit the sun and rotates once every 4.3 hours.

Scientists expect to further improve the assessment of Bennu’s Earth impact risk in 2037, when the asteroid will make a close approach to Earth and allow them to collect radar data.

A computer-generated image of the OSIRIS-REx probe collecting a sample from the surface of the asteroid Bennu. The spacecraft is due to return to Earth with the sample in 2023.
NASA’s Goddard Space Flight Center