Bennu’s near-Earth lifetime of 1.75 million years inferred from craters on its boulders

Ballouz, Ronald-Louis; Walsh, K. J.; Barnouin, Olivier S.; DellaGiustina, D. N.; Asad, M. Al; Jawin, E. R.; Daly, M. G.; Bottke, W. F.; Michel, Patrick; Avdellidou, Chrysa; Delbò, M.; Daly, R. T.; Asphaug, Erik; Bennett, C. A.; Bierhaus, E. B.; Connolly, H. C.; Golish, D. R.; Molaro, J. L.; Nolan, M. C.; Pajola, M.; Rizk, B.; Schwartz, S. R.; Trang, D.; Wolner, C. W. V.; Лауретта, Д. С.

doi:10.1038/s41586-020-2846-z

Cited by 80 publications

(71 citation statements)

References 54 publications

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“…This is exemplified by the complex structures of boulders on near-Earth asteroids (101955) Bennu and (162173) Ryugu, as recently revealed by high-spatial resolution images obtained by NASA's and JAXA's sample return missions OSIRIS-REx and Hayabusa2, respectively (DellaGiustina et al 2019;Jaumann et al 2019;Lauretta et al 2019aLauretta et al , 2019bSugita et al 2019). In particular, the discovery of craters in the surfaces of Bennu's boulders revealed the effects of meteoroid impacts on this asteroid, which occurred only in the last 1.75 Myr (Ballouz et al 2020). Furthermore, recent analyses of the main asteroid belt have revealed that only a very limited number of the asteroids that we catalog today have survived intact from primordial times (Delbo et al 2017), whereas the large majority of asteroids are fragments (Dermott et al 2018) that experienced disruption of their parent bodies and reaccumulation (Michel 2001;Michel and Richardson 2013;Michel et al 2020).…”

Section: Introductionmentioning

confidence: 89%

The astrophysical context of collision processes in meteorites

Marrocchi

Delbò

Gounelle

2021

Meteorit & Planetary Scien

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Chondrites are leftover solids from the early evolution of the solar protoplanetary disk that never experienced melting since their formation. They comprise unequilibrated assemblages of low-and high-temperature components, including volatile-rich, fine-grained matrices, Fe-Ni metal, sulfides, refractory inclusions, and chondrules. Consequently, chondrites are commonly described as pristine, primitive, or primordial rocks of the solar system. However, impact-generated secondary features are abundant in chondrites, suggesting that collisions among early-formed planetesimals and their fragmentation and reassembly have been effective throughout the evolution of the solar system. In this report, we review evidence of the major role of impacts in generating the current mineralogical and petrographic characteristics of chondrites. We provide perspective to these meteoritic features by discussing recent analyses of large-scale structures of the main asteroid belt and remote-sensing observations of asteroids. Observations at various spatial scales all attest that the "primitive" materials formed during the evolution of the solar system have largely been reprocessed, confirming previous studies that primitivity is relative, not absolute. This implies that (1) chondrites (and some differentiated meteorites) should systematically be envisioned as reprocessed and heterogeneous materials and (2) brecciated meteorites should be considered the norm and unbrecciated meteorites the exception.

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Section: Introductionmentioning

confidence: 89%

The astrophysical context of collision processes in meteorites

Marrocchi

Delbò

Gounelle

2021

Meteorit & Planetary Scien

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“…They also yield insights into cratering mechanics. Cratering on Bennu occurs in a challenging‐to‐understand regime that pushes the frontiers of our understanding of impact mechanics: gravity is very small (Lauretta et al, 2019; Scheeres et al, 2019); target strength is low (Ballouz et al, 2020; Lauretta et al, 2019; Scheeres et al, 2019) but poorly known and could vary with depth (Barnouin, Daly, Palmer, et al, 2019); target porosity is high (Barnouin, Daly, Palmer, et al, 2019; Scheeres et al, 2019); and the target surface is coarse grained and boulder rich (Barnouin, Daly, Palmer, et al, 2019; DellaGiustina et al, 2019; Lauretta et al, 2019; Walsh et al, 2019).…”

Section: Introductionmentioning

confidence: 99%

“…Craters range in size from ~160 m (Walsh et al, 2019) to as small as several centimeters. These smallest craters were discovered on the faces of boulders (Ballouz et al, 2020). Impact craters have a variety of interior morphologies, which have been attributed to local variations in the preimpact boulder population and the size of the craters relative to the boulders (Bierhaus et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

The Morphometry of Impact Craters on Bennu

Daly

Bierhaus

Barnouin

et al. 2020

Geophysical Research Letters

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Bennu is an~500-m-diameter rubble-pile asteroid that is the target of detailed study by the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer (OSIRIS-REx) mission. Here we use data from the OSIRIS-REx Laser Altimeter to assess depth-to-diameter ratios (d/D) of 108 impact craters larger than 10 m in diameter. The d/D of craters on Bennu ranges from 0.02 to 0.19. The mean is 0.10 ± 0.03. The smallest craters show the broadest range in d/D, consistent with d/D measurements on other asteroids. A few craters have central mounds, which is interpreted as evidence that a more competent substrate lies a few meters beneath them. The range of d/D narrows as crater size increases, with craters larger than 80 m tending toward smaller d/D. At large scales, increases in target strength with depth, combined with target curvature, may affect crater morphometry.

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“…The differences in albedo generally correspond to two primary boulder populations that dominate Bennu's rubble-covered surface (DellaGiustina et al 2019(DellaGiustina et al , 2020. Rocks on Bennu are broken down by processes such as thermal fatigue (Molaro et al 2020) and meteoroid bombardment (Bottke et al 2020;Ballouz et al 2020).…”

Section: Introductionmentioning

confidence: 99%

In search of Bennu analogs: Hapke modeling of meteorite mixtures

Merlin

Deshapriya

Fornasier

et al. 2021

A&A

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Context. The OSIRIS-REx Visible and InfraRed Spectrometer onboard the Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer spacecraft obtained many spectra from the surface of the near-Earth asteroid (101955) Bennu, enabling the characterization of this primitive small body. Bennu is spectrally similar to the hydrated carbonaceous chondrites (CCs), but questions remain as to which CCs, or combinations thereof, offer the best analogy to its surface. Aims. We aim to understand in more detail the composition and particle size of Bennu’s surface by refining the relationship between this asteroid and various CC meteorites. Methods. We used published absorbance and reflectance data to identify new optical constants for various CC meteorites measured in the laboratory at different temperatures. We then used the Hapke model to randomly generate 1000 synthetic spectra in order to find the combinations of these potential meteoritic analogs that best reproduce the spectral features of the asteroid. Results. Our investigations suggest that the surface of Bennu, though visibly dominated by boulders and coarse rubble, is covered by small particles (tens to a few hundreds of μm) and that possibly dust or powder covers the larger rocks. We further find that the surface is best modeled using a mixture of heated CM, C2-ungrouped, and, to some extent, CI materials. Conclusions. Bennu is best approximated spectrally by a combination of CC materials and may not fall into an existing CC group.

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Bennu’s near-Earth lifetime of 1.75 million years inferred from craters on its boulders

Cited by 80 publications

References 54 publications

The astrophysical context of collision processes in meteorites

The astrophysical context of collision processes in meteorites

The Morphometry of Impact Craters on Bennu

In search of Bennu analogs: Hapke modeling of meteorite mixtures

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