Bennu is a carbonaceous asteroid in the Apollo group discovered by the LINEAR Project on September 11, 1999. It has a cumulative 1-in-2,700 chance of impacting Earth between 2175–2199.It is the planned target of the OSIRIS- REx mission which is intended to return samples to Earth in 2023 for further study.Physical description:Asteroid Bennu has a roughly spheroidal shape, which resembles a spinning top. The direction of rotation about its axis is retrograde with respect to its orbit. Bennu has a fairly smooth shape with one prominent 10–20 m boulder on its surface, in the southern hemisphere.There is a well-defined ridge along the equator of asteroid Bennu. The presence of this ridge suggests that fine-grained regolith particles have accumulated in this area, possibly because of its low gravity and fast rotation.Observations of this minor planet by the Spitzer space telescope in 2007 gave an effective diameter of 484±10 m, which is in line with other studies. It has a low visible geometric albedo of 0.046±0.005. The thermal inertia was measured and found to vary by ±19% during each rotational period. The data suggest that the regolith grain size is moderate, ranging from several millimeters up to a centimeter, and evenly distributed longitudinally. No emission from a potential dust coma has been detected around asteroid Bennu, which puts a limit of 106 g of dust within a radius of 4750 km.Astronomic observations between 1999 and 2013 have demonstrated that 101955 Bennu is influenced by the yarkovsky effect, causing the semi major axis to drift on average by 284±1.5 meters/year. Analysis of the gravitational and thermal effects has given a bulk density of ρ = 1260±70 kg/m3, which is only slightly denser than water. Therefore, the predicted macroporosity is 40±10%, suggesting that the interior has a rubble pile structure. The estimated mass is (7.8±0.9)×1010 kg.
Origin and evolution
carbonaceous material that composes asteroid Bennu originally came from dying stars such as red gaints and supernova. According to the accretion theory, this material came together 4.5 billion years ago during the formation of the solar system.Asteroid 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 into more complex minerals. Bennu probably began in the inner asteroid belt as a fragment from a larger body with a diameter of 100 km. 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 resonance 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.
on average, an asteroid with diameter of 500 m (1,600 ft; 0.31 mi) can be expected to impact Earth about every 130,000 years or so. A 2010 dynamical study by Andrea Milani and collaborators predicted a series of eight potential Earth impacts by Bennu between 2169 and 2199.
The cumulative probability of impact is dependent on physical properties of Bennu that were poorly known at the time, but was not found to exceed 0.071% for all eight encounters. The authors recognized that an accurate assessment of 101955 Bennu's probability of Earth impact would require a detailed shape model and additional observations (either from the ground or from spacecraft visiting the object) to determine the magnitude and direction of the Yarkovsky effect.The publication of the shape model and of astrometry based on radar observations obtained in 1999, 2005, and 2011, made possible an improved estimate of the Yarkovsky acceleration and a revised assessment of the impact probability. The current (as of 2014) best estimate of the impact probability is a cumulative probability of 0.037% in the interval 2175 to 2196. This corresponds to a cumulative score on the Palermo scale of −1.71. If an impact were to occur, the expected kinetic energy associated with the collision would be 1,200 megatons in TNT equivalent.
2060Bennu will pass 0.005 AU (750,000 km; 460,000 mi) from Earth on 23 September 2060. The close approach of 2060 causes divergence in the close approach of 2135. On 25 September 2135 the nominal approach distance is 0.002 AU (300,000 km; 190,000 mi) from Earth, but Bennu could pass as close as 0.0007 AU (100,000 km; 65,000 mi). There is no chance of an Earth impact in 2135.The 2135 approach will create many lines of variations and Bennu may pass through a gravitational keyhole during the 2135 passage which could create an impact scenario at a future encounter. The keyholes are all less than 55 km wide.On 25 September 2175 there is a 1 in 24,000 chance of an Earth impact, but the nominal 2175 approach is in February 2175 at a distance of roughly 0.1 AU (15,000,000 km; 9,300,000 mi) The most threatening virtual impactor is on 24 September 2196 when there is a 1 in 11,000 chance of an Earth impact. There is a cumulative 1 in 2,700 chance of an Earth impact between 2175–2199.
SpaceApps is a NASA incubator innovation program.