A new class of coordinatively unsaturated, monomeric organoscandium compounds, Cp*2Sc-R (Cp* = (rj5-C5Me5); R = halide, hydride, alkyl, alkenyl, alkynyl, aryl), has been prepared. Cp*2Sc-Cl is obtained from reaction of ScCl3(THF)3 (THF = tetrahydrofuran) with LiCp*, and Cp*2Sc-R (R = CH3, C6H5, C6H4CH3, CH2C6H5) from treatment of Cp*2Sc-Cl with the appropriate organoalkali reagent. These organoscandium compounds react with dihydrogen rapidly to yield R-H and Cp*2Sc-H. The tetrahydrofuran adducts Cp*2ScX(THF) (X = Cl, H, CH3) are obtained upon treatment of Cp*2Sc-X with tetrahydrofuran. Rapid exchange of dihydrogen with the hydride ligands of Cp*2Sc-H and Cp*2ScH(THF) occurs even at low temperatures. Other alkyl derivatives may be conveniently prepared by treatment of Cp*2Sc-H (or Cp*2ScH(THF)) with -olefins, e.g., Cp*2ScCH2CH3 from Cp*2Sc-H and ethylene. Aliene and Cp*2Sc-H afford Cp*2Sc(7j3-C3H5). Cp*2Sc-R (R = H, CH3, aryl) reacts with pyridine to yield Cp*2Sc(C, N-j;2-C5H4N), which crystallizes in the orthorhombic space group

NASA’S Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) spacecraft recently arrived at near-Earth asteroid (101955) Bennu, a primitive body that represents the objects that may have brought prebiotic molecules and volatiles such as water to Earth [ 1 ]. Bennu is a low-albedo B-type asteroid [ 2 ] that has been linked to organic-rich hydrated carbonaceous chondrites [ 3 ]. Such meteorites are altered by ejection from their parent body and contaminated by atmospheric entry and terrestrial microbes. Thus, the primary mission objective is to return a sample of Bennu to Earth that is pristine, i.e., not affected by these processes [ 4 ]. The OSIRIS-REx spacecraft carries a sophisticated suite of instruments to characterize Bennu’s global properties; support selection of a sampling site; and document that site at sub-centimeter scales [ 5 - 11 ]. Here we consider early observations to understand how Bennu’s properties compare to pre-encounter expectations and the prospects for sample return. The bulk composition of Bennu appears to be hydrated and volatile-rich, as expected. However, in contrast to pre-encounter modeling of Bennu’s thermal inertia [ 12 ] and radar polarization ratios [ 13 ]—which indicated a generally smooth surface covered by centimeter-scale particles—resolved imaging reveals an unexpected surficial diversity. The albedo, texture, particle size, and roughness are beyond the spacecraft design specifications. On the basis of our pre-encounter knowledge, we developed a sampling strategy to target 50-m-diameter patches of loose regolith with grain sizes less than 2 cm [ 4 ]. We observe only a small number of apparently hazard-free regions, on the order of 5 to 20 meters in extent, the sampling of which poses a substantial challenge to mission success.

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In May of 2011, NASA selected the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) asteroid sample return mission as the third mission in the New Frontiers program. The other two New Frontiers missions are New Horizons, which explored Pluto during a flyby in July 2015 and is on its way for a flyby of Kuiper Belt object 2014 MU69 on Jan. 1, 2019, and Juno, an orbiting mission that is studying the origin, evolution, and internal structure of Jupiter. The spacecraft departed for near-Earth asteroid (101955) Bennu aboard an United Launch Alliance Atlas V 411 evolved expendable launch vehicle at 7:05 p.m. EDT on September 8, 2016, on a seven-year journey to return samples from Bennu. The spacecraft is on an outbound-cruise trajectory that will result in a rendezvous with Bennu in August 2018. The science instruments on the spacecraft will survey Bennu to measure its physical, geological, and chemical properties, and the team will use these data to select a site on the surface to collect at least 60 g of asteroid regolith. The team will also analyze the remote-sensing data to perform a detailed study of the sample site for context, assess Bennus resource potential, refine estimates of its impact probability with Earth, and provide ground-truth data for the extensive astronomical data set collected on this asteroid. The spacecraft will leave Bennu in 2021 and return the sample to the Utah Test and Training Range (UTTR) on September 24, 2023.Comment: 89 pages, 39 figures, submitted to Space Science Reviews - OSIRIS-REx special issu

The shapes of asteroids reflect interplay between their interior properties and the processes responsible for their formation and evolution as they journey through the Solar System. Prior to the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer) mission, Earth-based radar imaging gave an overview of (101955) Bennu’s shape. Here, we construct a high-resolution shape model from OSIRIS-REx images. We find that Bennu’s top-like shape, considerable macroporosity, and prominent surface boulders suggest that it is a rubble pile. High-standing, north-south ridges that extend from pole to pole, many long grooves, and surface mass wasting indicate some low levels of internal friction and/or cohesion. Our shape model indicates that, similar to other top-shaped asteroids, Bennu formed by reaccumulation and underwent past periods of fast spin leading to its current shape. Today, Bennu might follow a different evolutionary pathway, with interior stiffness permitting surface cracking and mass wasting.

High-resolution radar images reveal near-Earth asteroid (66391) 1999 KW4 to be a binary system. The approximately 1.5-kilometer-diameter primary (Alpha) is an unconsolidated gravitational aggregate with a spin period approximately 2.8 hours, bulk density approximately 2 grams per cubic centimeter, porosity approximately 50%, and an oblate shape dominated by an equatorial ridge at the object's potential-energy minimum. The approximately 0.5-kilometer secondary (Beta) is elongated and probably is denser than Alpha. Its average orbit about Alpha is circular with a radius approximately 2.5 kilometers and period approximately 17.4 hours, and its average rotation is synchronous with the long axis pointed toward Alpha, but librational departures from that orientation are evident. Exotic physical and dynamical properties may be common among near-Earth binaries.

The MIT Faculty has made this article openly available. Please share how this access benefits you. Your story matters. CitationHamilton, V.E., et al., "Evidence for widespread hydrated minerals on asteroid (101955) Bennu." Nature astronomy 3, 4 (2019): p.

We determine the three-dimensional shape of near-Earth asteroid (101955) Bennu based on radar images and optical lightcurves. Bennu was observed both in 1999 at its discovery apparition, and in 2005 using the 12.6-cm radar at the Arecibo Observatory and the 3.5-cm radar at the Goldstone tracking station. Data obtained in both apparitions were used to construct a shape model of this object. Observations were also obtained at many other wavelengths to characterize this object, some of which were used to further constrain the shape modeling (Clark et al., 2011;Hergenrother et al., 2013; Krugly et al., 1999). The lightcurve data, along with an initial determination of the rotation period derived from them, simplified and improved the shape modeling.Below we briefly describe the observations and shape modeling process. We discuss the shape model and the implications for the possible formation and evolution of this object. We also describe the importance and limitations of the shape model in view of the fact that this object is the target of the OSIRIS-REx spacecraft mission.