BENNU SAMPLE PHYSICAL PROPERTIES FROM MULTI-SCALE MEASUREMENTS OF STRENGTH
AND INDENTATION HARDNESS. C. G. Hoover
1
, K. J. Jardine
1
, A. J. Ryan
2
, P. Sánchez
3
, J. Biele
4
, R-L.
Ballouz
5
, R. J. Macke
6
, Z. A. Landsman
7
, J. M. Long-Fox
7
, H. C. Connolly Jr.
2,8,9
, D. S. Lauretta
2
.
1
Arizona State
University, Tempe, AZ, USA (Christian.Hoo[email protected]),
2
Lunar and Planetary Laboratory, University of Arizona,
Tucson, AZ, USA,
3
University of Colorado Boulder, Boulder, CO, USA,
4
German Aerospace Center (DLR), Köln,
Germany,
5
Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA,
6
Vatican Observatory, Vatican
City State,
7
Department of Physics, University of Central Florida, Orlando, FL, USA,
8
Department of Geology, Rowan
University, Glassboro, NJ, USA,
9
Department of Earth and Planetary Science, American Museum of Natural History,
New York, NY, USA.
Introduction: NASA’s OSIRIS-REx mission to
Bennu [1], a carbonaceous asteroid, returned samples to
Earth on September 24, 2023. A series of tests will be
performed to determine the physical and thermal
properties and the effects of nano-sized inclusions on
the micro-scale properties of the returned sample [2].
These collected data will test a subset of mission
hypotheses related to the formation, geological
evolution, and fundamental nature of Bennu and its
parent body (see chapter 3 in [2]), formulated through
analysis of remote sensing data. Strength results will
help us understand the evolution of Bennu’s surface in
response to impacts, thermal fracturing, and mass
wasting [2]. Strength and energy absorption values will
help determine if the energetic events (sample collection
and return) possibly influenced the sample [3].
Elasticity and strength results will help inform asteroid
deflection strategies, such as the recent DART mission,
by providing quantities needed to calculate momentum
and energy transfer during collisions. The following
overview focuses on a subset of these tests: the nano-
and micro-scale mechanical tests, with preliminary
results from tests with analog materials.
Nano- and Micro-scale Testing Program: We
plan to perform (i) nano- and micro-scale indentation,
(ii) compression testing, and (iii) cohesion testing [4].
Here, we present an overview of the indentation and
compression testing. As part of preparations for sample
return, we performed tests on carbonaceous chondrite
materials, which can act as analogs to Bennu material
based on infrared remote sensing data analysis [5,6,7].
Two practice materials were indented: a 30-μm section,
prepared at NASA’s Johnson Space Center (JSC) of the
Lonewolf Nunataks 94102 (LON 94102) meteorite
(Fig. 1, a-c), and a 50-µm section, also prepared at JSC,
of a Bennu-like CM terrestrial simulant, similar to [8]
but with a higher total porosity of ~54%. Compression
tests were performed on the CM simulant.
Preliminary results of indentation testing:
Instrumented nanoindentation, consists of pushing a
diamond Berkovich tip into the surface of a material and
recording the force vs. displacement response, allows
for the properties of the returned rocks (on a scale down
to ~5–10 nm) to be elucidated thanks to phase
separability [9]. Micro-indentation is the same style of
test with larger forces and penetration depths, yielding
a more homogenized response. The modulus (M) and
hardness (H) of the indented material(s) are determined
using the Oliver and Pharr model [10].
Nano-scale indentation tests were performed on
LON 94102, using a force-controlled testing protocol
with a max force of 8 mN. A collection of measurements
on and around a stiff particle (Fig. 1c) resulted in the
force vs. displacement curves (Fig. 1d). Most of the
indents on the particle had shallow footprints around
150 nm deep, giving an M and H of 183.2 ± 44 GPa and
12.5 ± 3.56 GPa, respectively. Indents on the clay
matrix (Fig. 1e) were deeper, for the same maximum
force, due to the compliant behavior of the clay,
resulting in wider footprints and an M and H of 46.7 ±
7.3 GPa and 2.67 ± 0.61 GPa, respectively.
Micro-indentation was performed on the CM
simulant. These indents reached depths of ~2.9 µm at 8
gram-force, yielding an M of 18.22 ± 5.93 GPa and H
of 0.49 ± 0.14 GPa. Our results are consistent with
findings from other heterogeneous materials including
cements and organic-rich source rocks [9,11,12].
Preliminary results of compression. Compressing a
particle between two rigid metallic platens is a common
technique for quantitative determination of particle-
scale strength [13]. The scale of this test will be on the
order of a few hundred μm to mm, depending on the size
distribution of particles in the allocated aggregate. The
micro-indenter will compress the sample with a “flat
punch” probe with controlled displacement up to a max
depth. The output of each test is a force vs. displacement
curve (Fig. 2a). XCT scans will show if there are large
pre-existing flaws within the particles that could
concentrate stresses as singularities and nucleate cracks.
In our test with the CM simulant, the average particle
diameter in Fig. 2b was 0.95 mm and the max force (Fig.
2a) was 186 mN, yielding a splitting tensile strength of
184 kPa. The test resulted in fragmentation of the main
specimen into several smaller pieces (Fig. 2c), all of
which were recoverable for future analysis.
Outlook for Bennu sample analysis: Preliminary
examination of the returned rocks has confirmed the
carbonaceous nature of Bennu and revealed the samples
to be heterogeneous in nature [14]; therefore, the
response to any excitation on larger scales of the sample
is a combination of the effects across multiple material
phases on smaller scales.
2480.pdf55th LPSC (2024)
Acknowledgments: This material is based upon
work supported by NASA under Contract
NNM10AA11C issued through the New Frontiers
Program. We are grateful to the entire OSIRIS-REx
Team for making the return of samples from Bennu
possible.
References: [1] Lauretta, D.S. et al. (2021) in
Sample Return Missions, ed. A. Longobardo (Elsevier):
163-194. [2] Lauretta D.S. et al. (2023)
arXiv:2308.11794. [3] Ballouz R.-L. et al. (2024) this
conf.
[4] Jardine et al. (2024) This Conference [4]
Hamilton V.E. et al. (2019) Nat. Astron., 3, 332-340. [5]
Kaplan H.H. et al. (2020) MAPS, 55, 744-765. [6]
Lauretta D.S. et al. (2022) Science, 377, 285-291. [7]
Avdellidou C. et al. (2020) Icarus, 341, 113648.
[8] Ulm F. J. et al. (2010) Cem. Concr. Compos., 32, 92-
99. [9] Oliver W.C. & Pharr G.M. (2004) J. Mater.
Res., 19, 3-20. [10] Hoover C.G. & Ulm F.J. (2015)
Cem. Concr. Res., 75, 42-52. [11] Abedi S. et al. (2016)
Acta Geotech., 11, 559-572. [12] Huang Q. et al. (2020)
Geosci. Front., 11, 401-411. [13] Zhao R. et al. (2023)
J. Rock Mech. Geo. Eng., 15, 2280-2290. [14] Lauretta,
D.S., et al. (2023) ACG Shoemaker Lecture
Fig. 1:
(a-c) Progressively magnified view of LON 94102
meteorite thin section with 405 indents performed on
embedded stiff particle (c), resulting in (d) collection of force
vs. displacement curves. (e) 400 indents in the fine-grained
clay matrix.
Fig. 2:
(a) Force vs. displacement curve from compression
of simulant sample. (b) Simulant sample inside of
compression testing machine, outlined by red circle. (c)
Smaller fragments of simulant sample formed during
compression tests, outlined by red circles.
2480.pdf55th LPSC (2024)
