Asteroid (101955) Bennu’s weak boulders and thermally anomalous equator

Abstract

Thermal inertia and surface roughness are proxies for the physical characteristics of planetary surfaces. Global maps of these two properties distinguish the boulder population on near-Earth asteroid (NEA) (101955) Bennu into two types that differ in strength, and both have lower thermal inertia than expected for boulders and meteorites. Neither has strongly temperature-dependent thermal properties. The weaker boulder type probably would not survive atmospheric entry and thus may not be represented in the meteorite collection. The maps also show a high–thermal inertia band at Bennu’s equator, which might be explained by processes such as compaction or strength sorting during mass movement, but these explanations are not wholly consistent with other data. Our findings imply that other C-complex NEAs likely have boulders similar to those on Bennu rather than finer-particulate regoliths. A tentative correlation between albedo and thermal inertia of C-complex NEAs may be due to relative abundances of boulder types.

Spectral effects of varying texture and composition in two‐component “mudpie” simulations: Insights for asteroid (101955) Bennu

“…This interpretation is consistent with results from thermal analysis presented by Rozitis et al. (2020), showing that an areal dust layer <50 µm thick covering 5–10% of the surface could be consistent with their observations. In addition, Hamilton et al.…”

In search of Bennu analogs: Hapke modeling of meteorite mixtures

“…Considering that the surface of Bennu is dominated by boulders with little apparent fine-grained regolith (Lauretta et al 2019;DellaGiustina et al 2019), these small particle sizes suggest a coating of fine particulates on top of the boulder surface, supporting other findings from OSIRIS-REx data: Independent analyses of OTES observations (Hamilton et al 2020) suggest that the spectral differences observed over Bennu's global surface could be attributable to the presence of a thin layer of fine particulates (<65-100 µm). The sizes retrieved by their models are consistent with thermal inertia results that limit any dust coating on Bennu's boulder-covered surface to <50 µm (Rozitis et al 2020a).…”

Particle Size-Frequency Distributions of the OSIRIS-REx Candidate Sample Sites on Asteroid (101955) Bennu

“…In early observations of Bennu, DellaGiustina and Emery et al [24] found evidence of a multimodal particle population having distinct normal albedo ranges and PSFDs. Recent work has confirmed the presence of at least two distinct particle populations on the basis of spectral, geomorphologic [58], and thermal [62] analyses: (i) a high-reflectance, high-thermal-inertia population of smooth, angular particles, all of which are smaller than~20 m, and (ii) a more common low-reflectance, low-thermal-inertia population of rough, hummocky particles that spans the full-size range of measured objects (up to~100 m). Both are present within the candidate sample sites (Figure 11) [63] suggesting that Bennu's heterogeneity [58] extends to small scales (<1 m).…”