Asteroid

Bennu

The asteroid NASA's OSIRIS-REx sampled and brought to Earth in 2023, and one of the two most hazardous known asteroids.

Bennu, a mosaic of OSIRIS-REx images
Image: NASA/Goddard/University of Arizona

At a glance

Size
~490 m across
Impact risk
On NASA's impact-risk list · 1 in 1,700 chance of impact, 2178–2290
Close approaches and the impact-risk list

Missions to Bennu

From discovery to the flyby

  1. September 8, 2016
    Launches as OSIRIS-REx
    OSIRIS-APEX
  2. December 3, 2018
    Arrives at asteroid Bennu (as OSIRIS-REx)
    OSIRIS-APEX
  3. October 20, 2020
    Collects a sample from Bennu
    OSIRIS-APEX
  4. May 10, 2021
    Leaves Bennu for Earth (as OSIRIS-REx)
    OSIRIS-APEX
  5. September 24, 2023
    Delivers the Bennu sample to Earth
    OSIRIS-APEX

A small piece of Bennu is now in laboratories on Earth. NASA's OSIRIS-REx spacecraft collected rock and dust from its surface on 20 October 2020 and dropped the sample capsule in Utah on 24 September 2023.[1] The capsule held 121.6 g of material, more than twice the mission's requirement and the largest asteroid sample ever collected in space.[2]

A fragment of an older world

Bennu is about 500 m across, about a third of a mile.[3] Its rocks formed nearly 4.6 billion years ago on a larger body that was later destroyed in a giant collision, and Bennu gathered from part of the leftover rubble about 1 to 2 billion years ago.[1] It comes closest to Earth every 6 years, passing within about 299,000 km, less than the distance to the Moon.[1]

What the sample contains

Analyses of the sample found 14 of the 20 amino acids that life on Earth uses to build proteins, and all five nucleobases that life uses to store genetic information in DNA and RNA.[4] Scientists also found traces of 11 minerals that form when salty water evaporates, evidence of brines on Bennu's parent body.[4] The findings are not evidence of life, but they suggest that the conditions for life's chemistry were widespread in the early solar system.[4]

The impact risk, in numbers

Bennu is one of the two most hazardous known asteroids, along with 1950 DA.[3] Using OSIRIS-REx tracking data, NASA researchers put its total chance of hitting Earth through the year 2300 at about 1 in 1,750, or 0.057%.[3] The single most significant date is 24 September 2182, with a chance of about 1 in 2,700.[3]

Those odds depend on a close approach to Earth in 2135, when Earth's gravity will bend Bennu's path; the question is whether it passes through a small region of space, called a keyhole, that would set up a later impact.[3] Even sunlight matters: as Bennu's warmed surface cools, it gives off heat that pushes the asteroid with a force NASA compares to the weight of three grapes, enough to shift its path noticeably over long periods.[3] How such odds are worked out is explained in Impact risk.

Sources

  1. [1]NASA, 101955 Bennu — science.nasa.gov, retrieved October 26, 2026
  2. [2]NASA, OSIRIS-REx — science.nasa.gov, retrieved October 26, 2026
  3. [3]NASA, NASA Spacecraft Provides Insight into Asteroid Bennu's Future Orbit — nasa.gov, retrieved October 26, 2026
  4. [4]NASA, NASA's Asteroid Bennu Sample Reveals Mix of Life's Ingredients — nasa.gov, retrieved October 26, 2026

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