9 research outputs found
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 Bennuâs 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 Bennuâs surface has been most recently migrating towards its equator (given Bennuâs increasing spin rate), we infer that Bennuâs 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 Bennuâs 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 Bennuâs 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 2.7â”m 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 2.4â”m) Bennuâs 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
Momentum transfer from the DART mission kinetic impact on asteroid dimorphos
The NASA Double Asteroid Redirection Test (DART) mission performed a kinetic impact on asteroid Dimorphos, the satellite of the binary asteroid (65803) Didymos, at 23:14 UTC on September 26, 2022 as a planetary defense test1. DART was the first hypervelocity impact experiment on an asteroid at size and velocity scales relevant to planetary defense, intended to validate kinetic impact as a means of asteroid deflection. Here we report the first determination of the momentum transferred to an asteroid by kinetic impact. Based on the change in the binary orbit period2, we find an instantaneous reduction in Dimorphos's along-track orbital velocity component of 2.70 ± 0.10 mm s-1, indicating enhanced momentum transfer due to recoil from ejecta streams produced by the impact3,4. For a Dimorphos bulk density range of 1,500 to 3,300 kg m-3, we find that the expected value of the momentum enhancement factor, [Formula: see text], ranges between 2.2 and 4.9, depending on the mass of Dimorphos. If Dimorphos and Didymos are assumed to have equal densities of 2,400 kg m-3, [Formula: see text]. These [Formula: see text] values indicate that significantly more momentum was transferred to Dimorphos from the escaping impact ejecta than was incident with DART. Therefore, the DART kinetic impact was highly effective in deflecting the asteroid Dimorphos
Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface
Small, kilometre-sized near-Earth asteroids are expected to have young and frequently refreshed surfaces for two reasons: collisional disruptions are frequent in the main asteroid belt where they originate, and thermal or tidal processes act on them once they become near-Earth asteroids. Here we present early measurements of numerous large candidate impact craters on near-Earth asteroid (101955) Bennu by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) mission, which indicate a surface that is between 100 million and 1 billion years old, predating Bennuâs expected duration as a near-Earth asteroid. We also observe many fractured boulders, the morphology of which suggests an influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface. However, the surface also shows signs of more recent mass movement: clusters of boulders at topographic lows, a deficiency of small craters and infill of large craters. The oldest features likely record events from Bennuâs time in the main asteroid belt
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 ”m 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 ”m) Bennuâs 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
Craters, boulders and regolith of (101955) Bennu indicative of an old and dynamic surface
Small, kilometre-sized near-Earth asteroids are expected to have young and frequently refreshed surfaces for two reasons: collisional disruptions are frequent in the main asteroid belt where they originate, and thermal or tidal processes act on them once they become near-Earth asteroids. Here we present early measurements of numerous large candidate impact craters on near-Earth asteroid (101955) Bennu by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) mission, which indicate a surface that is between 100 million and 1 billion years old, predating Bennuâs expected duration as a near-Earth asteroid. We also observe many fractured boulders, the morphology of which suggests an influence of impact or thermal processes over a considerable amount of time since the boulders were exposed at the surface. However, the surface also shows signs of more recent mass movement: clusters of boulders at topographic lows, a deficiency of small craters and infill of large craters. The oldest features likely record events from Bennuâs time in the main asteroid belt
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 NASAâs Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show that asteroid (101955) Bennuâs surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given Bennuâs 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 Bennuâs surface particles span from the disruption of the asteroidâs 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 Bennuâs 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 Bennuâs surface has been most recently migrating towards its equator (given Bennuâs increasing spin rate), we infer that Bennuâs 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 Bennuâs 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 Bennuâs top-shape morphology and its link to the formation of binary asteroids
Properties of rubble-pile asteroid (101955) Bennu from OSIRIS-REx imaging and thermal analysis
International audienceEstablishing 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 NASAâs Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) spacecraft, we show that asteroid (101955) Bennuâs surface is globally rough, dense with boulders, and low in albedo. The number of boulders is surprising given Bennuâs 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 Bennuâs surface particles span from the disruption of the asteroidâs parent body (boulders) to recent in situ production (micrometre-scale particles)