101955 Bennu

radar images in 1999 showing Bennu's rotation Bennu was discovered on 11 September 1999 during a Near-Earth asteroid survey by the Lincoln Near-Earth Asteroid Research (LINEAR). Bennu was observed extensively by the Arecibo Observatory and the Goldstone Deep Space Network using radar imaging as Bennu closely approached Earth on 23 September 1999. == Physical characteristics ==

in December 2018.|left Bennu has a roughly spheroidal shape, resembling a spinning top. Bennu's axis of rotation is tilted 178 degrees to its orbit; the direction of rotation about its axis is retrograde with respect to its orbit. The veins range from 3 to 15 centimeters wide, and can be over one meter in length, much bigger than carbonate veins seen in meteorites. The estimated mass is . Photometry and spectroscopy Photometric observations of Bennu in 2005 yielded a synodic rotation period of . It has a B-type classification, which is a sub-category of carbonaceous asteroids. Polarimetric observations show that Bennu belongs to the rare F subclass of carbonaceous asteroids, which is usually associated with cometary features. including carbonaceous-chondrite mineral magnetite. Magnetite, a spectrally prominent water product but destroyed by heat, including OSIRIS-REx staff. Water According to Dante Lauretta, OSIRIS-REx Principal Investigator, "Bennu appears to be a very water-rich target, and water is the most interesting and perhaps the most lucrative commodity that you would mine from an asteroid". Predicted beforehand, Dante Lauretta (University of Arizona) reiterates that Bennu is water-rich- already detectable while OSIRIS-REx was still technically in approach. dominated by phyllosilicates. Phyllosilicates, among others, hold water. Bennu's water spectra were detectable on approach, reviewed by outside scientists, then confirmed from orbit. A separate estimate, including other forms of water storage, is 6.2 wt%. NASA and university sample facilities are preparing to secure, study, and curate the sample, predicted to be rich in water and organic compounds. The German SAL (Sample Analysis Laboratory) is preparing to receive cosmochemical water from Ryugu, Bennu, and other airless bodies. Activity Bennu is an active asteroid, sporadically emitting plumes of particles and rocks as large as (not dust, defined as tens of micrometers). Scientists hypothesize the releases may be caused by thermal fracturing, volatile release through dehydration of phyllosilicates, pockets of subsurface water, are examples of active asteroids. If the IAU declares Bennu to be a dual-status object, its comet designation would be P/ (LINEAR). Surface features All geological features on Bennu are named after various species of birds and bird-like figures in mythology. On 6 March 2020 the IAU announced the first official names for 12 Bennu surface features, including regiones (broad geographic regions), craters, dorsa (ridges), fossae (grooves or trenches) and saxa (rocks and boulders). Analysis showed that the particles making up Bennu's exterior are loosely packed and lightly bound to each other; "The spacecraft would have sunk into Bennu had it not fired its thrusters to back away immediately after it grabbed dust and rock from the asteroid's surface." Analysis also revealed that the Sun's heat fractures rocks on Bennu in just 10,000 to 100,000 years instead of millions of years as was thought before. Candidate sample sites After a thorough analysis of Bennu's surface by the OSIRIS-REx mission team, using data from both MapCam and OVIRS, four candidate sites were selected for sample collection: Nightingale, Kingfisher, Osprey, and Sandpiper. Among these, Nightingale was ultimately chosen, as it exhibited a stronger spectral reddening compared to the rest of the surface (indicating fresher or less exposed terrain). Additionally, it successfully passed the safety assessment tests for the spacecraft's descent. On 12 December 2019, after a year of mapping Bennu's surface, a target site was announced. Named Nightingale, the area is near Bennu's north pole and lies inside a small crater within a larger crater. Osprey was selected as the backup sample site. IAU named features == Origin and evolution ==

The carbonaceous material that composes Bennu originally came from the breakup of a much larger parent body—a planetoid or a proto-planet. But like nearly all other matter in the Solar System, the origins of its minerals and atoms are to be found in dying stars such as red giants and supernovae. According to the accretion theory, this material came together 4.5 billion years ago during the formation of the Solar System. Bennu's basic mineralogy and chemical nature would have been established during the first 10 million years of the Solar System's formation, where the carbonaceous material underwent some geologic heating and chemical transformation inside a much larger planetoid or a proto-planet capable of producing the requisite pressure, heat and hydration (if need be)—into more complex minerals. Simulations suggest a 70% chance it came from the Polana family and a 30% chance it derived from the Eulalia family. Subsequently, the orbit drifted as a result of the Yarkovsky effect and mean motion resonances with the giant planets, such as Jupiter and Saturn. Various interactions with the planets in combination with the Yarkovsky effect modified the asteroid, possibly changing its spin, shape, and surface features. == Orbit ==

Bennu orbits the Sun with a period of . though another estimate is 20–30 megatons). The 2021 orbit solution extended the virtual impactors from the year 2200 to the year 2300 and slightly increased the cumulative Palermo impact hazard scale rating to −1.42. The solution included the estimated gravitational effect of 343 other asteroids, representing about 90% of the total mass of the main asteroid belt. The next two biggest risks occur in 2187 (1:14,000) and 2192 (1:26,000). There is a cumulative 1 in 1,800 chance of an Earth impact between 2178 and 2290. Long term Lauretta et al. reported in 2015 their results of a computer simulation, concluding that it is more likely that 101955 Bennu will be destroyed by some other cause: The orbit of Bennu is intrinsically dynamically unstable, as are those of all NEOs. In order to glean probabilistic insights into the future evolution and likely fate of Bennu beyond a few hundred years, we tracked 1,000 virtual "Bennus" for an interval of 300 Myr with the gravitational perturbations of the planets Mercury–Neptune included. Our results ... indicate that Bennu has a 48% chance of falling into the Sun. There is a 10% probability that Bennu will be ejected out of the inner Solar System, most likely after a close encounter with Jupiter. The highest impact probability for a planet is with Venus (26%), followed by the Earth (10%) and Mercury (3%). The odds of Bennu striking Mars are only 0.8% and there is a 0.2% chance that Bennu will eventually collide with Jupiter. Meteor shower As an active asteroid with a small minimum orbit intersection distance from Earth, Bennu may be the parent body of a weak meteor shower. Bennu particles would radiate around 25 September from the southern constellation of Sculptor. The meteors are expected to be near the naked eye visibility limit and only produce a Zenith hourly rate of less than 1. == Exploration ==

OSIRIS-REx The OSIRIS-REx mission of NASA's New Frontiers program was launched towards on 8 September 2016. On 3 December 2018, the spacecraft arrived at the asteroid Bennu after a two-year journey. One week later, at the American Geophysical Union Fall Meeting, investigators announced that OSIRIS-REx had discovered spectroscopic evidence for hydrated minerals on the surface of the asteroid, implying that liquid water was present in Bennu's parent body before it split off. On 7 April 2021, OSIRIS-REx completed its final flyover of the asteroid and began slowly drifting away from it. On 10 May 2021, the departure was completed with OSIRIS-REx still managing to contain the asteroid sample. On 13 December 2023, further studies of the returned sample were reported and revealed organic molecules as well as unknown materials which require more study to have a better idea of their composition and makeup. On 11 January 2024, NASA reported finally fully opening, after three months of trying, the recovered container with samples from the Bennu asteroid. The total weight of the recovered material weighed , over twice the mission's goal. On 15 May 2024, an overview of preliminary analytical studies on the returned samples was reported. Selection The asteroid Bennu was selected from over half a million known asteroids by the OSIRIS-REx selection committee. The primary constraint for selection was close proximity to Earth, since proximity implies low impulse (Δv) required to reach an object from Earth orbit. The elemental composition of the Bennu samples closely resembles that of CI chondrite meteorites. However, the Bennu material shows some distinct isotopic ratios. The average oxygen isotopic composition places Bennu in the same region of oxygen three-isotope space as CI and CY chondrites, as well as samples from asteroid Ryugu. The carbon content of the samples (4.5–4.7 wt%) is higher than that found in known meteorites and Ryugu samples. The presence of presolar grains in the samples indicates that some of the material has remained largely unprocessed since the formation of the solar system. Presolar silicon carbide and graphite were identified, with abundances of and respectively, similar to unheated chondrite samples. Another portion of the sample was exhibited by NASA at the International Astronautical Congress in Milan, Italy, from 14 to 18 October 2024. In January 2025, it was reported that a wide range of carbon- and nitrogen-rich organic compounds have been identified in samples returned from Bennu, including 14 of the 20 amino acids that make up proteins in terrestrial organisms, as well as all five nucleobases (adenine, thymine, cytosine, guanine, and uracil) that are the essential building blocks of DNA and RNA. == See also ==