Astronomers, thanks to ground-based telescopes and the OSIRIS-REx interplanetary station, have estimated the danger of the 500-meter near-Earth asteroid Bennu for the Earth. It turned out that the highest probability of an asteroid colliding with our planet in one chance in 2700 belongs to September 2182, which makes Bennu the most dangerous object on the Palermo scale. The article was published in the Icarus magazine.
(101955) Bennu was discovered in 1999 and classified as potentially hazardous to the Earth. It repeatedly approached our planet, which made it possible to conduct its radar observations, and in 2016 the OSIRIS-REx interplanetary station was sent to Bennu, which for 2, 5 years of work mapped the asteroid, determined its properties, found out that Bennu was active, found it on its surface is split boulders, fragments of the asteroid Vesta and organic matter, and also traced the course of its evolution. In addition, the device took soil from the northern hemisphere of the asteroid, the total mass of the collected material was 400 grams.
A group of planetary scientists led by Davide Farnocchia from NASA's Jet Propulsion Laboratory published a paper where they clarified the evolution of the asteroid's orbit and the likelihood of its collision with the Earth, using both observational data from ground-based telescopes and data obtained by OSIRIS-REx. Scientists have built a new model, in which the Yarkovsky effect plays an important role, which affects the orbital drift, and also took into account the Poynting-Robertson effect, which has so far been considered in the context of the dynamics of interplanetary dust.
It turned out that the change in the length of the semi-major axis of the orbit due to the Yarkovsky effect is ± one meter per year, as Bennu's orbit evolves due to gravitational disturbances from the planets from 1900 to 2135. At the same time, the solar wind resistance can reduce the magnitude of the semi-major axis drift to 0.16 meters per year. The probability of a collision with the Earth of Bennu before 2300 is estimated at one chance in 1750, and the highest probability of one chance in 2700 refers to September 2182, which corresponds to a value of -1.6 on the Palermo scale, making Bennu the most dangerous object. Previously, the first place belonged to the asteroid (29075) 1950 DA, which had a value of -1.4 on the Palermo scale. Bennu's future approach to Earth in 2037 will make it possible to re-refine its orbit through radar observations.
Currently, OSIRIS-REx has left Bennu and is on its way to Earth. The reentry capsule with asteroid soil is expected to land at the Utah test site on September 24, 2023.