101955 Bennu

Discovering and Naming 101955 Bennu

Bennu, the ancient Egyptian mythological bird associated with the Sun, creation, and rebirth, was discovered on September 11, 1999. This asteroid, officially designated as 101955 (provisional designation 1999 RQ36), is a carbonaceous asteroid in the Apollo group. It’s not just any space rock; it’s a potentially hazardous object with a cumulative 1-in-1,750 chance of impacting Earth between 2178 and 2290.

Physical Characteristics

Bennu has a mean diameter of 490 meters. Its surface is rougher than initially thought, with over 200 boulders larger than 10 meters on its surface. The rotation period decreases by about one second every 100 years due to the Yarkovsky-O’Keefe-Radzievskii-Paddack effect. This means that Bennu is an active asteroid, sporadically emitting plumes of particles and rocks as large as 10 centimeters.

Orbital Dynamics

Bennu orbits the Sun every 1.19 years, getting as close as 480,000 kilometers from Earth’s orbit. It is expected to impact Earth about every 130,000 years, with predicted impacts between 2169 and 2199. The asteroid’s orbit has been perturbed due to interactions with the planets, potentially changing its spin, shape, and surface features.

Sample Return Mission

The OSIRIS-REx mission successfully returned samples to Earth in September 2023. These samples are predominantly very dark, with reflectance values consistent with observations of Bennu’s surface. The sample contains black dust and debris, as well as organic molecules and unknown materials that require further study.

Scientific Discoveries

The recovered sample is rich in hydrated minerals, particularly Mg-rich phyllosilicates, magnetite, sulfides, carbonates, and organic compounds. An unexpected discovery was the presence of phosphate minerals in some samples, including Mg, Na-rich phosphates found as veins and crusts in some particles.

Orbital Stability and Impact Risk

The long-term stability of Bennu’s orbit is uncertain due to its dynamically unstable nature. Computer simulations suggest that it may be destroyed by other causes before becoming a threat to Earth. Bennu has a 48% chance of falling into the Sun, a 10% probability that it will be ejected out of the inner Solar System, and the highest impact probabilities are with Venus (26%), Earth (10%), Mercury (3%). The odds of Bennu striking Mars are 0.8%, while Jupiter is at a 0.2% chance.

Conclusion

Bennu, this ancient space bird, holds secrets from the early days of our solar system. Its journey through time and space offers us a glimpse into the origins of life on Earth. As we continue to study Bennu, we uncover not just rocks but pieces of history itself.