The dynamic geophysical environment of (101955) Bennu based on OSIRIS-REx measurements

The top-shaped morphology characteristic of asteroid (101955) Bennu, often found among fast-spinning asteroids and binary asteroid primaries, may have contributed substantially to binary asteroid formation. Yet a detailed geophysical analysis of this morphology for a fast-spinning asteroid has not been possible prior to the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission. Combining the measured Bennu mass and shape obtained during the Preliminary Survey phase of the OSIRIS-REx mission, we find a notable transition in Bennu’s surface slopes within its rotational Roche lobe, defined as the region where material is energetically trapped to the surface. As the intersection of the rotational Roche lobe with Bennu’s surface has been most recently migrating towards its equator (given Bennu’s increasing spin rate), we infer that Bennu’s surface slopes have been changing across its surface within the last million years. We also find evidence for substantial density heterogeneity within this body, suggesting that its interior is a mixture of voids and boulders. The presence of such heterogeneity and Bennu’s top shape are consistent with spin-induced failure at some point in its past, although the manner of its failure cannot yet be determined. Future measurements by the OSIRIS-REx spacecraft will provide insight into and may resolve questions regarding the formation and evolution of Bennu’s top-shape morphology and its link to the formation of binary asteroids

Evidence for widespread hydrated minerals on asteroid (101955) Bennu

Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the visible and near-infrared (0.4 to 2.4 µm) Bennu’s spectrum appears featureless and with a blue (negative) slope, confirming previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic chemistry to Earth

Halogens in chondritic meteorites and terrestrial accretion

Volatile element delivery and retention played a fundamental role in Earth’s formation and subsequent chemical differentiation. The heavy halogens (Cl, Br and I) are key tracers of accretionary processes due to their high volatility and incompatibility, but have low abundances in most geological and planetary materials. Noble gas proxy isotopes produced during neutron irradiation provide a high sensitivity tool for the determination of heavy halogen abundance. Here we show that Cl, Br and I abundances in carbonaceous, enstatite, Rumuruti and primitive ordinary chondrites have concentrations ~6, ~9 and between 15-37 times lower, respectively, than previously reported and most commonly accepted estimates1. This is independent of the chondrites’ oxidation state or petrological type. Bromine/Cl and I/Cl in all studied chondrites show a limited range, indistinguishable from bulk silicate Earth (BSE) estimates. Our results demonstrate that BSE depletion of halogens relative to primitive meteorites is now consistent with lithophile elements of similar volatility. The new results for carbonaceous chondrites demonstrate that late accretion, constrained to a maximum of 0.5 ± 0.2 % of Earth’s silicate mass2–5, cannot solely account for present-day terrestrial halogen inventories6,7. It is estimated that 80−90% of heavy halogens are concentrated in Earth’s surface reservoirs7,8 and have not undergone the extreme early loss observed in atmosphere-forming elements9. Therefore, in addition to late accretion of halogens and mantle degassing, which is <50% efficient over Earth history10, efficient extraction of halogen-rich fluids6 from the solid Earth during the earliest stages of Earth formation is also required. The hydrophilic nature of the halogens supports this requirement, and is consistent with a volatile/water rich late-stage terrestrial accretion</p

Evidence for widespread hydrated minerals on asteroid (101955) Bennu

Early spectral data from the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission reveal evidence for abundant hydrated minerals on the surface of near-Earth asteroid (101955) Bennu in the form of a near-infrared absorption near 2.7 µm and thermal infrared spectral features that are most similar to those of aqueously altered CM-type carbonaceous chondrites. We observe these spectral features across the surface of Bennu, and there is no evidence of substantial rotational variability at the spatial scales of tens to hundreds of metres observed to date. In the visible and near-infrared (0.4 to 2.4 µm) Bennu’s spectrum appears featureless and with a blue (negative) slope, confirming previous ground-based observations. Bennu may represent a class of objects that could have brought volatiles and organic chemistry to Earth