Properties of Rubble-Pile Asteroid (101955) Bennu from OSIRIS-REx Imaging and Thermal Analysis

Establishing the abundance and physical properties of regolith and boulders on asteroids is crucial for understanding the formation and degradation mechanisms at work on their surfaces. Using images and thermal data from NASA's Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show that asteroid (101955) Bennu's surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given Bennu's moderate thermal inertia, suggesting that simple models linking thermal inertia to particle size do not adequately capture the complexity relating these properties. At the same time, we find evidence for a wide range of particle sizes with distinct albedo characteristics. Our findings imply that ages of Bennu's surface particles span from the disruption of the asteroid's parent body (boulders) to recent in situ production (micrometre-scale particles)

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

Evaluation of the data base from high power and low power small break LOCA counterpart tests performed in LOBI, SPES, BETHSY and LSTF facilities

An experimental data base relevant to scaling in nuclear thermal-hydraulics was created and discussed in this report. The Integral Test Facilities (ITF) considered are LOBI, BETHSY, SPES and LSTF. The same Small Break Loss of Coolant Accident (SBLOCA) accident scenario was measured in the four facilities. However six experiments were performed because in each of LOBI and SPES ITF two test were carried out. The former (in each case) was the ‘low’ initial power consistent with the power in the two ITF, the latter (in each case) was the ‘high’ initial power exploiting the capabilities of both SPES and LOBI (in terms of maximum scaled power available). The gathered database includes three main parts: • Geometrical and material configuration of ITF • Boundary and initial conditions for the 6 experiments • Selected time trends (about 50) during the experiments The database constitutes a milestone achievement for the demonstration of thermal-hydraulic system code capabilities addressing the scaling issue. The database outlined in the above abstract is updated and qualified by a new activity as discussed in the present document

Application of the Cathare 2 v1.3U code to the analysis of the Pactel GDE-34 experiment relevant to the innovative reactors EU Meeting, London (UK), June 2-3, 1997

Following (and based on) the demonstration of adequate capabilities of Relap5 code in predicting situations which are relevant for the prediction of transient performance advanced reactors, the same activity was planned in relation to the CATHARE code. CATHARE is the French code developed by CEA in Grenoble in cooperation with FRAMATOME and EdF governmental French Companies. UNIPI also contributed to the development of the code (e.g. by sending junior researchers to the CENG Center in Grenoble). The present activity deals with the application of the code to the experiment GDE-34 performed in the Finnish Integral Test Facility (ITF) PACTEL which was modified with the introduction of passive systems, namely Core Make-up Tank (CMT)