# Simulated asteroid materials based on carbonaceous chondrite mineralogies

Daniel T. Britt, Kevin M. Cannon, Kerri Donaldson Hanna, Joanna

Hogancamp, Olivier Poch, Pierre Beck, Dayl Martin, Jolantha Eschrig, Lydie

Bonal, Philip T. Metzger

► To cite this version:

Daniel T. Britt, Kevin M. Cannon, Kerri Donaldson Hanna, Joanna Hogancamp, Olivier Poch, et al. Simulated asteroid materials based on carbonaceous chondrite mineralogies. Meteoritics and Planetary Science, 2019, 54, pp.2067-2082. 10.1111/maps.13345. insu-03703556

HAL Id: insu-03703556

https://insu.hal.science/insu-03703556v1

Submitted on 20 Aug 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Simulated asteroid materials based on carbonaceous chondrite mineralogies

Daniel T. BRITT<fnref n="1" />, Kevin M. CANNON ID<fnref n="1" />*, Kerri DONALDSON HANNA<fnref n="1" />,<fnref n="2" />,
Joanna HOGANCAMP<fnref n="3" />, Olivier POCH<fnref n="4" />, Pierre BECK<fnref n="4" />, Dayl MARTIN<fnref n="5" />, Jolantha ESCRIG<fnref n="4" />,
Lydie BONAL<fnref n="4" />, and Philip T. METZGER<fnref n="1" />,<fnref n="6" />

*(Received 14 March 2019; revision accepted 30 May 2019)*

**Abstract**—A set of high-fidelity simulated asteroid materials, or simulants, was developed based on the mineralogy of carbonaceous chondrite meteorites. Three varieties of simulant were developed based on CI1 chondrites (typified by Orgueil), CM2 chondrites (typified by Murchison), and CR2/3 chondrites (multiple samples). The simulants were designed to replicate the mineralogy and physical properties of the corresponding meteorites and anticipated asteroid surface materials as closely as is reasonably possible for bulk amounts. The simulants can be made in different physical forms ranging from larger cobbles to fine-grained regolith. We analyzed simulant prototypes using scanning electron microscopy, X-ray fluorescence, reflectance spectroscopy at ambient conditions and in vacuum, thermal emission spectroscopy in a simulated asteroid environment chamber, and combined thermogravimetry and evolved gas analysis. Most measured properties compare favorably to the reference meteorites and therefore to predicted volatile-rich asteroid surface materials, including boulders, cobbles, and fine-grained soils. However, there were also discrepancies, and mistakes were made in the original mineral formulations that will be updated in the future. The asteroid simulants are available to the community from the nonprofit Exolith Lab at UCF, and the mineral recipes are freely published for other groups to reproduce and modify as they see fit.

## INTRODUCTION

Only a handful of spacecraft have come close enough to directly interact with the surface material of an asteroid, but this will be changing in the near future. Both the Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) and Hayabusa2 missions are attempting to sample material from the surfaces of C-complex asteroids (Tsuda et al. 2013; Lauretta et al. 2019), the Asteroid Impact and Deflection Assessment mission will use a kinetic impactor to deflect a near-Earth asteroid (NEA; Cheng et al. 2015), and a burgeoning group of commercial companies has plans to extract resources

from NEAs and use these resources to support a space-based economy (Metzger et al. 2013; Graps et al. 2017). There are compelling science reasons to study asteroid regoliths. Their compositions and physical properties provide valuable information about the nebular environment and planetary building blocks, and about diverse processes including impact cratering (e.g., Miyamoto et al. 2007), space weathering (e.g., Clark et al. 2002), Yarkovsky and YORP effects (e.g., Vokrouhlický et al. 2015), aqueous alteration and thermal heating (e.g., Keil 2000), and regolith formation itself (e.g., Delbo et al. 2014). For practical applications, many C-complex asteroids contain abundant mineral-bound OH and H₂O (Rivkin 2012) that can be used to

<footnote n="1">¹Department of Physics, University of Central Florida, Orlando, Florida 32816, USA</footnote>

<footnote n="2">²Atmospheric, Oceanic and Planetary Physics, Oxford University, Oxford OX1 4BH, UK</footnote>

<footnote n="3">³Geocontrols Systems, Jacobs JETS Contract at NASA Johnson Space Center, Houston, Texas 77058, USA</footnote>

<footnote n="4">⁴Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France</footnote>

<footnote n="5">⁵European Space Agency, ECSAT, Fermi Avenue, Harwell Campus, Oxfordshire OX11 0FD, UK</footnote>

<footnote n="6">⁶Florida Space Institute, Orlando, Florida 32826, USA</footnote>

<footnote>*Corresponding author. E-mail: cannon@ucf.edu</footnote>
produce propellants (Lewis 1996), and regolith of any
composition can be used as radiation shielding (Pohl
and Britt 2017) or as a construction material for
structures in space (Mueller et al. 2016). However,
currently there is no bulk asteroid material available to
support scientific experiments or technology maturation
for asteroid missions. The original Hayabusa mission
returned ~1500 grains from the asteroid Itokawa's
surface: these were invaluable for linking the petrology
of ordinary chondrites to S-complex asteroids (Nakamura
et al. 2011), but material from sample return missions is
too precious for bulk regolith studies and for developing
and testing hardware for future missions. Additionally,
regoliths on S-complex asteroids likely differ substantially
from the more volatile-rich (i.e., ≥1 wt% equivalent
H₂O) surfaces of C-complex asteroids that are currently
a focus for many current and future missions. The
objective of this work is to develop and characterize
simulated C-complex asteroid materials, or simulants,
based on the mineralogy and physical properties of
well-characterized carbonaceous chondrite meteorites.

In the past, many regolith simulants with well-
known acronyms have been produced for the Moon
(e.g., JSC-1; McKay et al. 1994, NU-LHT; Stoeser
et al. 2010) and Mars (e.g., JSC Mars-1; Allen et al.
1998, MGS-1; Cannon et al. 2019); a listing is maintained
at http://sciences.ucf.edu/class/planetary-simulant-database/.
Asteroid simulants have been developed in a more ad hoc
way, and no standardized simulants currently exist.
Metzger et al. (2019) provided a detailed list of past efforts
to simulate asteroid surface materials: in many cases, these
are low-fidelity substitutes such as glass beads, lunar
simulant, and bread flour, among others. In the first effort
to systematically create high-fidelity asteroid simulants, the
University of Central Florida (UCF) and Deep Space
Industries (DSI; now part of Bradford Space) developed a
series of prototypes with physical forms including solid
cobbles and regolith. Originally, these simulants were sold
for profit by DSI; however, after closing their Orlando
facility, the simulant production and distribution have been
absorbed by the Center for Lunar & Asteroid Surface
Science (CLASS) at UCF and transitioned to a nonprofit
distribution model. The goal of the rebranded Exolith Lab
(https://sciences.ucf.edu/class/exolithlab/) is to produce and
distribute a line of standardized simulants for asteroids, the
Moon, and Mars (Cannon et al. 2019). In addition, we
maintain a library of raw minerals to rapidly prototype
customized versions for specific cases. In this contribution,
three asteroid simulants are described (Fig. 1) based on (1)
highly volatile-rich CI carbonaceous chondrites (CI
Asteroid Simulant), (2) moderately volatile-rich CM
carbonaceous chondrites (CM Asteroid Simulant), and (3)
less volatile-rich CR carbonaceous chondrites (CR
Asteroid Simulant).

<figure><img src="image_2.png" /><figcaption>Fig. 1. Photographs of the asteroid simulants created in this work, in regolith form. a) CI simulant based on the Orgueil meteorite. b) CM simulant based on the Murchison meteorite. c) CR simulant based on an average of five CR chondrites. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

SIMULANT DESIGN PHILOSOPHY

Composition and physical property measurements
of carbonaceous chondrites provide a reference model
from which to develop simulated C-complex asteroid
materials, keeping in mind that some asteroids or
portions thereof may not be represented in the known
meteorite collection. Current thinking links carbonaceous
chondrites to the C-complex asteroids as parent bodies
(e.g., Johnson and Fanale 1973; Rivkin 2012). These
meteorite samples—particularly the CIs, CMs, and
many CRs—currently provide the best source of
information on the anticipated mineralogy and physical
properties of volatile-rich asteroid surface material.
Remote sensing of low-albedo asteroids provides
somewhat limited compositional information, especially
<table><caption>Table 1. Quantitative mineralogy of reference meteorites determined by PSD-XRD.</caption><thead><tr><th>Phase</th><th>Orgueil (CI1)<sup>a</sup></th><th>Murchison (CM2)<sup>a</sup></th><th>Murchison (CM2)<sup>b</sup></th><th>PCA 91082 (CR2)<sup>c</sup></th><th>GRA 95229 (CR2)<sup>c</sup></th><th>LAP 02342 (CR2)<sup>c</sup></th><th>QUE 99177 (CR3)<sup>c</sup></th><th>GRA 06100 (CR2)<sup>c</sup></th></tr></thead><tbody><tr><td>Saponite-serpentine</td><td>64.2</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Magnetite</td><td>9.7</td><td>0.4</td><td>1.1</td><td></td><td></td><td></td><td>0.9</td><td>0.2</td></tr><tr><td>Mg-rich serpentine</td><td>7.3</td><td>22.8</td><td>22.2</td><td>15.3</td><td>8.8</td><td>7.1</td><td>1.5</td><td>11.4</td></tr><tr><td>Olivine</td><td>7.2</td><td>11.6</td><td>15.1</td><td>26.5</td><td>37.6</td><td>43.7</td><td>36.7</td><td>40.1</td></tr><tr><td>Ferrihydrite</td><td>5.0</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Fe-sulfide</td><td>6.6</td><td>3.4</td><td>1.9</td><td>4.7</td><td>3.2</td><td>3.4</td><td>5.3</td><td>7.1</td></tr><tr><td>Fe-rich serpentine</td><td></td><td>58.5</td><td>50.3</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Pyroxene</td><td></td><td>2.2</td><td>8.3</td><td>31.6</td><td>36.8</td><td>28.3</td><td>35.9</td><td>33.0</td></tr><tr><td>Calcite</td><td></td><td>0.1</td><td>1.2</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>Fe,Ni metal</td><td></td><td></td><td></td><td>3.6</td><td>6.2</td><td>7.1</td><td>5.6</td><td>2.7</td></tr><tr><td>X-ray amorphous Fe-rich</td><td></td><td></td><td></td><td>18.5</td><td>7.8</td><td>10.8</td><td>14.1</td><td>5.8</td></tr><tr><td>Oxide (magnetite + rust)</td><td></td><td></td><td></td><td>2.0</td><td>7.0</td><td>4.0</td><td>3.0</td><td>6.0</td></tr></tbody></table>

mineral-based approach, and these issues and future remedies are described in more detail below.

## Physical Properties

The physical properties of asteroid surface materials are controlling factors for developing spacecraft hardware that will interact with these bodies: grapple, anchor, land, rove, and excavate. Physical properties, therefore, must be considered for realistic simulants. Asteroids are covered in an unconsolidated regolith with polymineralic grains ranging in size from microns to massive boulders. There appears to be a distinct trend of decreasing average grain size with increasing mass, or gravity field of the asteroid (Gundlach and Blum 2013), such that smaller asteroids are blockier while larger bodies retain more fines and may closely resemble the lunar surface in terms of regolith texture. Initial imagery from the Hayabusa2 and OSIRIS-REx missions suggests smaller C-complex asteroid surfaces are indeed strewn with large cobbles and boulders (Fig. 2d).

Our asteroid simulants are not simply a mixed powder of the minerals in Table 2, but have been developed to broadly replicate different forms of asteroid surface materials including larger cobbles (Fig. 2c) and finer grained regolith (Fig. 1). The physical properties of carbonaceous meteorites offer clues about the nature of coherent, lithified C-complex asteroid materials. These meteorites have been characterized extensively in terms of

density and porosity (Britt and Consolmagno 2003; Consolmagno et al. 2008; Macke et al. 2011) and thermophysical properties (Opeil et al. 2010). Grain densities for CIs, CMs, and CRs vary between 2.20–2.38, 2.57–2.87, and 2.92–3.47 g cm⁻³, respectively; average porosities for these three types are 11.3%, 23.0%, and 6.4% (Britt and Consolmagno 2003). The grain densities are much lower than other chondrite types, and thermal conductivities are significantly lower as well (Opeil et al. 2010). Literature for compressive and tensile strengths of carbonaceous chondrites is severely limited. The available data (Pohl and Britt Forthcoming) suggest that they are much weaker than ordinary chondrites and iron meteorites, as might be expected. Strength varies among different carbonaceous chondrite types, with a general trend of CM > CI > Tagish Lake identified by Tsuchiyama et al. (2009). Compressive strengths cited for CIs are typically several MPa (similar to Styrofoam), while CMs can reach 50–100 MPa, stronger than concrete (Pohl and Britt Forthcoming). There are currently no strength data available for CRs.

## DEVELOPING PROTOTYPE SIMULANTS

To develop asteroid simulant prototypes, we (1) sourced the raw materials (Table 2; Fig. 2a) in as pure a form as possible from terrestrial mines and chemical suppliers; (2) comminuted, sieved, and analyzed the raw materials; (3) mixed the minerals for a given simulant

<footnote><sup>a</sup>From Bland et al. (2004), given as wt%.</footnote>

<footnote><sup>b</sup>From Howard et al. (2009), given as vol%.</footnote>

<footnote><sup>c</sup>From Howard et al. (2015), given as vol%.</footnote>
<table><caption>Table 2. Initial simulant recipes used to create prototypes, and suggested updates to the recipes based on analyses of these prototypes. All values in wt%.</caption><thead><tr><th>Mineral</th><th>CI prototype</th><th>CI future update</th><th>CM prototype</th><th>CM future update</th><th>CR prototype</th><th>CR future update</th></tr></thead><tbody><tr><td>Mg-serpentine</td><td>48.0</td><td>51.3</td><td>72.5</td><td>73.8</td><td>9.2</td><td>6.8</td></tr><tr><td>Epsomite</td><td>6.0</td><td>—</td><td>—</td><td>—</td><td>—</td><td>—</td></tr><tr><td>Magnetite</td><td>13.5</td><td>10.0</td><td>10.4</td><td>5.0</td><td>14.3</td><td>2.5</td></tr><tr><td>Palygorskite</td><td>5.0</td><td>5.3</td><td>—</td><td>—</td><td>—</td><td>—</td></tr><tr><td>Olivine</td><td>7.0</td><td>7.0</td><td>7.8</td><td>11.2</td><td>33.7</td><td>33.1</td></tr><tr><td>Pyrite</td><td>6.5</td><td>7.0</td><td>2.6</td><td>3.3</td><td>4.1</td><td>5.8</td></tr><tr><td>Vermiculite</td><td>9.0</td><td>9.6</td><td>—</td><td>—</td><td>—</td><td>—</td></tr><tr><td>Coal</td><td>5.0</td><td>5.0</td><td>3.6</td><td>3.6</td><td>2.0</td><td>2.0</td></tr><tr><td>Pyroxene</td><td>—</td><td>—</td><td>2.1</td><td>2.1</td><td>31.6</td><td>29.6</td></tr><tr><td>Siderite</td><td>—</td><td>—</td><td>1.0</td><td>1.0</td><td>—</td><td>—</td></tr><tr><td>Iron metal</td><td>—</td><td>—</td><td>—</td><td>—</td><td>4.6</td><td>10.6</td></tr><tr><td>Nickel metal</td><td>—</td><td>—</td><td>—</td><td>—</td><td>0.5</td><td>—</td></tr><tr><td>Ferrihydrite</td><td>—</td><td>4.8</td><td>—</td><td>—</td><td>—</td><td>—</td></tr><tr><td>Amorphous silicate</td><td>—</td><td>—</td><td>—</td><td>—</td><td>—</td><td>9.6</td></tr></tbody></table>

according to the recipes in Table 2 to form a dry mixture (Fig. 2a); (4) bound the minerals with water and in some cases a binder to form a malleable paste (Fig. 2b); (5) dried or cured the paste and crushed the resulting material to create cobbles and finer regolith (Figs. 1 and 2c). These steps are described in more detail below.

## Sourcing Raw Materials

Many of the minerals in Table 2 are available from terrestrial mine sources or chemical suppliers. In some cases, the pure minerals are sold commercially under obscure trade names, for example, palygorskite as the product MIN-U-GEL®. In other cases, the minerals are being quarried for aggregate, or they make up the host rock of precious metal deposits and are available as waste. Table S1 in supporting information lists the sourcing information for all the materials in our asteroid simulants; however, these specific sources are not an inherent property of the simulants and mineralogically appropriate alternatives can be used to re-create similar products.

## Preparing and Analyzing Raw Materials

The raw minerals (Fig. 2a; Tables 2 and S1) came from suppliers in a variety of physical forms (powders, flakes, rocks) and were processed and analyzed prior to combining them to create the prototype simulants. We used a variety of equipment including rock crushers, ball mills, and sieves to comminute and then separate the raw materials into fine-grained powders. Materials such as the serpentine and palygorskite came as micron-sized powders, approximating chondrite matrices and requiring no further processing. For the other minerals, the average grain sizes of our processed

raw materials are in the tens of micron range: this is larger than carbonaceous chondrite matrix, but this was deemed to be an acceptable trade given the difficulty in colloidal grinding for bulk quantities. We analyzed each raw ingredient using XRD, X-ray fluorescence (XRF), and VNIR reflectance spectroscopy to verify the mineralogy, quantitatively measure the chemistry, and identify any contaminants present. Minor contaminants were identified in many of the naturally sourced minerals and are listed in Table S1. In theory, it would be possible to synthesize pure versions of some of these phases from raw oxides, but this is not practical for large-scale production. The crystal chemistry of some natural terrestrial minerals also differs from minerals found in meteorites, with higher concentrations of Mg and Al, and lower amounts of Fe. Again, these discrepancies were judged to be reasonable given the trades involved in using a cost-effective approach to produce large amounts of simulant.

## Creating Dry Mixtures

After the raw source materials were processed, they were mixed together in the appropriate weight ratios (Table 2), resulting in homogeneous medium to dark gray powders (Fig. 2a). Mixing can be done using stirring tools or by hand at small scales; for larger scales, a concrete mixer is appropriate. The resulting dry mixtures can be stored in a sealed environment indefinitely and later processed into different physical forms as desired. For the prototypes described here, mixing was performed in a Kushlan Products 600 DD concrete mixer for 6–12 h at 28 rpm. Powders were added all at once sequentially. We did not make specific efforts to mitigate against humidity during mixing, but final products were stored in sealed watertight buckets.
<figure><img src="image_3.png" /><figcaption>Fig. 2. Production methods for the CI Asteroid Simulant. a) Dry mixture of the powdered raw mineral inputs. b) Paste made from combining the dry mixture with water. c) Dried and crushed cobbles of the CI simulant. d) Image of Ryugu's surface from the Hayabusa2 mission (contrast enhanced, scale bar 1 m); image credit: JAXA. (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

## Binding

In order to create cobbles and regolith grains with coherent strength, we needed to bind the dry mixtures together somehow. We originally experimented with a wide variety of methods. We found adding water to the dry mixtures of CI simulant (~1:4 ratio of water:mix by weight) resulted in a malleable paste (Fig. 2b). After air drying, the paste lost all added water and formed a solid material (Fig. 2c) with several MPa in unconfined compressive strength, matching measurements from CI chondrites (Metzger et al. 2019; Pohl and Britt Forthcoming). The clay species appear to be responsible for most of this strength, because we found mixtures with less clay were much less coherent upon drying. A modified procedure was needed for the CM and CR simulants, because their respective meteorite types are considerably stronger than CIs. To increase the strength of these two simulant types, we used sodium metasilicate to create an alkali-activated material (also known as a geopolymers). This involved dissolving solid

sodium metasilicate pentahydrate in water, mixing this solution with the dry mixture (in a similar 1:4 ratio), and curing at an elevated temperature (at least 75°C). The final strength of the cured blocks is a function of the concentration of sodium metasilicate used: 2–5% of the dry mixture mass results in blocks with tens of MPa compressive strength, although more work is ongoing to refine this relationship and compare these materials to actual CMs and CRs. At a 5 wt% level, the sodium metasilicate pentahydrate increases the SiO₂ content of the simulants by 1.46 wt% and the Na₂O content by 1.42 wt%, while the majority of the added water is lost (outgassed) during curing and polymerization.

## Forming Cobbles and Regolith

Once solid blocks were formed, they were crushed either with hand tools or mechanized crushing equipment. Crushing generally results in a power law particle size distribution (Turcotte 1986), and the minimum, mean, and maximum particle size can easily
be adjusted by sieving and by changing the duration/ intensity of crushing. We created two classes of physical forms for the asteroid simulants: cobbles (Fig. 2c) that are likely to be prevalent on smaller asteroids, and fine-grained regolith or soil (Figs. 1 and 3) that should dominate the surfaces of larger asteroids (Gundlach and Blum 2013). Cobbles for this work were created by comminution with a mallet, and fine-grained regolith was produced in a 14" flail-type rock crusher. Metzger et al. (2019) performed an in-depth analysis of the particle size distribution of the CI Asteroid Simulant in regolith form and compared it to available constraints from meteorite and asteroid observations.

## SIMULANT CHARACTERIZATION

We characterized the asteroid simulant prototypes using a variety of instrumental techniques relevant to remote sensing and future missions including resource extraction. A companion paper (Metzger et al. 2019) describes a rigorous effort to quantitatively assess the fidelity of the CI simulant using a modified version of the “Figure-of-Merit” approach developed by NASA for lunar simulants. That paper focused more on physical properties, while the analyses below address microscopic textures, bulk chemistry, VNIR reflectance spectra, thermal emission spectra, and volatile release properties for all three simulant varieties.

### Scanning Electron Microscopy

All three simulant prototypes were imaged using a LEO 1530 VP scanning electron microscope (SEM) at the European Space Agency's Advanced Manufacturing Laboratory to visualize the textures present in the polymineralic composite particles. The samples were prepared for imaging using carbon adhesive pads attached to SEM sample stubs. Two methods of preparation were used, resulting in a “heavily pressed” stub and a “sprinkled” sample stub for each simulant. The pressed stub was made by pressing the stub into bulk material and then gently tapping the stub to remove any excess material. The sprinkled stub was made by gently dropping the sample from a height of ~2 cm, with the stub held at a high angle relative to the infalling material. Preparing the samples using these different methods allows a qualitative assessment of some of the sample's physical properties, such as cohesiveness. Figure 3 shows two different views of the fine fraction (<1 mm) of the CI Asteroid Simulant: the sprinkled stub (Fig. 3a) and a magnified view of specific particles of the pressed stub (Fig. 3b). Particle shapes in this simulant are subrounded to highly angular, with

smaller particles and individual minerals being angular and larger particles being subrounded to subangular. Many of the larger particles (>50 µm) are agglomerates of smaller particles, and the finest particles (<10 µm) adhere to the surfaces of larger particles (Figs. 3a and 3b). The CM asteroid simulant has a similar distribution of particle shapes, but with many agglomerate particles in the <10 µm range. Individual minerals tend to be highly angular or platy, with agglomerate particles being more subrounded to subangular. On the sprinkled sample stub, the CM simulant fines (<5 µm) adhere together to form longer “chains” or more angular agglomerations than at larger grain sizes (Fig. 3c). The CR asteroid simulant has the greatest abundance of fines (<5 µm), which mostly adhere to larger particles and appear brighter in SEM images than most other particles (Fig. 3d). Many of the smallest particles (<0.5 µm) are spherical and strongly adhere to each other and to larger particles. There are fewer agglomerate particles <50 µm than the CI and CM simulants, but the shape of these larger particles remains comparable (i.e., subrounded to subangular).

### Bulk Chemistry

The bulk elemental chemistry of the prototype simulants was measured using crushed powders with a PANalytical Epsilon XRF spectrometer at UCF, operating in oxides mode. Expressing compositions of chondrites as oxides (SiO₂, MgO, etc.) instead of metals (Si, Mg) is common practice because these materials are dominated by oxygen-complexed cations. Because the simulants are not meant to reproduce the trace element or isotopic compositions of the reference meteorites, these were not measured. Table 3 reports the major element chemistry of the three prototypes. All three are chemically dominated by subequal amounts of SiO₂, MgO, and FeO_T, as is true of carbonaceous chondrites in general (Jarosewich 1990). Compared to carbonaceous chondrites, the simulants have significantly higher Na₂O and K₂O concentrations, a consequence of using terrestrial minerals as feedstocks as well as the sodium metasilicate used as a binder in the CM and CR simulants. Even though the simulants were not created as chemical analogs, their bulk chemistry is fairly accurate. However, the CR prototype is a notable exception: its unrealistically high magnetite content resulted in a bulk chemistry that is strongly enriched in FeO_T and depleted in SiO₂ relative to CR chondrites. As discussed below, this issue will be remedied by making changes to the mineral recipe. We did not measure the speciation of Fe (Fe⁰, Fe²⁺, Fe³⁺) in the simulants, but this will be done in the future with Mössbauer spectroscopy.
<figure><img src="image_4.png" /><figcaption>Fig. 3. Scanning electron micrographs showing composite polymineralic grains that make up the asteroid simulants in regolith form. a) Diversity of particle morphologies and sizes in the CI Asteroid Simulant. b) Zoom in of a CI composite particle. c) Fine-grained agglomerates in the CM Asteroid Simulant. d) Bright (i.e., heavy) fines coating the surface of a larger grain in the CR Asteroid Simulant. Scale bar is 200 µm in (a), 50 µm in (b), and 20 µm in (c) and (d).</figcaption></figure>

VNIR Reflectance Spectroscopy

Reflectance spectra of the prototype simulants were acquired at the Institut de Planétologie et d'Astrophysique de Grenoble using the spectrophotometer with variable incidence and emergence (SHINE) spectro-gonio radiometer. Spectra were acquired between 0.4 and 4.2 µm with an incidence angle of 0° and an emergence angle of 30°. For ambient condition measurements, samples were prepared by sieving the original simulant powder to <100 µm, then depositing the sieved powder on a 1-mm thick sample holder, and flattening the sample surface with a spatula. For vacuum conditions, the simulants were unsieved. Spectral measurements were performed in ambient conditions and in vacuum, which is important for reducing the effects of adsorbed atmospheric water that can strongly affect the 3-µm region in particular.

The resulting spectra are shown in Fig. 4, which offsets them for clarity but also presents the absolute reflectance at 1.25 µm, outside the region of any major absorption. All three simulant varieties have low reflectance values (<0.1) at all wavelengths. The spectra are generally flat, with distinct peaks near 0.8 µm attributed to maghemite contamination in the magnetite, and complex hydration absorptions associated with -OH stretching and H₂O bending in hydrated silicates between 2.7 and 3.6 µm. The CI simulant has a broad

and wide 3 µm absorption with a minimum at 2.9 µm, attributed to the combination of serpentine and smectite clays in the mineral recipe. By contrast, the CM simulant (dominated by serpentine) shows a much sharper absorption with a minimum at 2.74 µm, similar to the spectral properties of pure serpentines (Beck et al. 2018). The CR simulant, with minimal clay content, shows a small but noticeable shoulder at 2.7 µm. Neither the CM nor CR spectra have noticeable 0.7 µm absorptions as is seen in the corresponding meteorites (Beck et al. 2018), but this may be because of the Fe-rich nature of asteroidal serpentine that are not accurately replicated in the simulants. Additional absorptions are observed around 3.48 µm in the simulants and are attributed to aliphatic organic species present in the coal component (Kaplan and Milliken 2016). The CI simulant is the only one that shows significant changes between ambient and vacuum conditions (Fig. 4). In vacuum, the 3 µm absorption becomes sharper and more asymmetric, attributed to less absorbed atmospheric water. The vacuum measurement more faithfully captures the inherent spectral properties of the clay mixture in the CI simulant, and is better for comparing to remote spectra from asteroids.

There are broad similarities between the prototype simulant spectra and reflectance spectra acquired from the corresponding carbonaceous chondrite samples, but
<table><caption>Table 3. Simulant prototype major element bulk chemistry, as measured by XRF.</caption><thead><tr><th>Oxide</th><th>CI Simulant (wt%)</th><th>CM Simulant (wt%)</th><th>CR Simulant (wt%)</th></tr></thead><tbody><tr><td>SiO<sub>2</sub></td><td>25.0</td><td>32.5</td><td>19.3</td></tr><tr><td>TiO<sub>2</sub></td><td>0.5</td><td>0.3</td><td>0.4</td></tr><tr><td>Al<sub>2</sub>O<sub>3</sub></td><td>3.1</td><td>3.1</td><td>1.2</td></tr><tr><td>FeO<sub>T</sub></td><td>25.8</td><td>20.2</td><td>42.9</td></tr><tr><td>MnO</td><td>0.3</td><td>0.2</td><td>0.3</td></tr><tr><td>MgO</td><td>30.2</td><td>32.1</td><td>30.1</td></tr><tr><td>CaO</td><td>3.0</td><td>3.1</td><td>0.8</td></tr><tr><td>Na<sub>2</sub>O</td><td>6.4</td><td>6.2</td><td>3.3</td></tr><tr><td>K<sub>2</sub>O</td><td>0.4</td><td>0.2</td><td>0.1</td></tr><tr><td>P<sub>2</sub>O<sub>5</sub></td><td>0.4</td><td>0.4</td><td>0.4</td></tr><tr><td>Cr<sub>2</sub>O<sub>3</sub></td><td>0.2</td><td>0.2</td><td>0.1</td></tr><tr><td>SO<sub>3</sub></td><td>4.9</td><td>1.5</td><td>0.9</td></tr><tr><td>Total</td><td>100.0</td><td>100.0</td><td>100.0</td></tr></tbody></table>

important differences as well. Carbonaceous chondrite reflectance spectra are also dark and flat, and have complex absorptions in the 3-µm region attributed to hydrated silicates (Cloutis et al. 2011a, 2011b; Beck et al. 2018). However, there are mismatches between the absolute reflectance values of the simulants and the meteorites. The inset in Fig. 4 compares the ambient simulant measurements to multiple spectra of each chondrite type taken from the RELAB database, filtered to those that were measured from similar size splits (0–75, 0–100, or 0–125 µm) as the simulant samples (0–100 µm). The CM simulant falls within the range of meteorite measurements, but the CI simulant and particularly the CR simulant are darker than their corresponding reference meteorites. This is mostly due to the large amount of magnetite in the prototype recipes (Table 2) that is unrealistic and deviated from the original meteorite mineralogies (Table 1). As discussed further below, the excess of magnetite is an important issue to address in the future. It is also responsible for the distinct peaks in the spectra near 0.8 µm because of the concomitant maghemite contamination (Fig. 4); such peaks are not observed in meteorite spectra. As well, the detailed shapes of the 3-µm region absorptions differ between simulants and meteorites. This is likely due to differences in crystal chemistry of clay species and the specific ratios of saponite-like phases and serpentine-like phases in CIs, for example.

## Thermal Infrared Emission Spectroscopy

We acquired thermal infrared (TIR) emissivity measurements under ambient (“Earth-like”) and simulated asteroid environment (SAE) conditions using the planetary analogue surface chamber for asteroid and

lunar environment (PASCALE) chamber within the Planetary Spectroscopy Facility at the University of Oxford. The experimental setup and calibration are similar to that of the simulated lunar environment chamber (SLEC), which has been described previously by Thomas et al. (2012, 2014) and Donaldson Hanna et al. (2019). The environment chamber is mounted to the emission port of a Bruker VERTEX 70v Fourier transform infrared (FTIR) spectrometer using a cesium iodide (CsI) window. We measured thermal infrared spectra at a resolution of 4 $cm^{-1}$ from ~2400 to 200 $cm^{-1}$ (~5 to 50 µm) using a wide-range TIR beam splitter and a deuterated, L-alanine doped triglycine sulfate (DLaTGS) detector. We made three spectral measurements of each sample with each one including 250 scans, which produces a spectrum with sufficient signal-to-noise ratio such that we can uniquely identify features of 2% contrast from the noise. The final TIR spectrum for each sample is an average that has been calibrated using published methods (e.g., Ruff et al. 1997) and spectral measurements of a blackbody painted with Nextel high emissivity black paint at 340 and 360 K (e.g., Thomas et al. 2012, 2014).

Near-surface conditions experienced in the regolith of planetary bodies are simulated in PASCALE by controlling the atmospheric pressure and temperature inside the environmental chamber and the way in which we heat the samples. Previous laboratory studies have shown the environmental conditions under which samples

<figure><img src="image_5.png" /><figcaption>Fig. 4. Visible/near-infrared reflectance spectra of the asteroid simulants measured on the SHINE instrument. Spectra have been offset for clarity; solid lines show ambient condition spectra, while dashed lines show vacuum condition. The inset shows absolute reflectance at 1.25 µm for the simulants at ambient conditions (squares) compared to meteorite data from the RELAB database (circles = mean, bars = min/max). (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>
are measured impart observable spectral changes (e.g., Logan et al. 1973; Henderson and Jakosky 1994; Donaldson Hanna et al. 2012a, 2012b, 2017, 2019; Thomas et al. 2012). We simulated the Earth's nearly isothermal near-surface conditions by backfilling PASCALE with dry nitrogen gas ($N_2$) to an atmospheric pressure ~1000 mbar, maintaining an ambient temperature inside the chamber (~300 K), and heating the sample from below to 353 K. These laboratory conditions are most comparable to emissivity measurements available in other spectral libraries including those in the Arizona State University spectral library (e.g., Christensen et al. 2000). We simulated a thermal gradient similar to that experienced in an asteroid near surface environment by evacuating the chamber to vacuum pressures (<10⁻⁴ mbar), by cooling the interior of the chamber to <125 K using liquid nitrogen ($LN_2$), and by heating the samples from above to a maximum brightness temperature of ~350 K and below to 353 K.

We crushed and sieved each asteroid simulant to particle sizes <75 µm to measure the thermal emission spectra (Fig. 5) of the fine particulate regolith-like simulant. We prepared each of the samples in a repeatable manner to limit the observed spectral differences to the composition and physical properties of the samples. Our techniques are similar to those used in other laboratory facilities to make our measurements comparable to literature values (e.g., Donaldson Hanna et al. 2017, 2019). We poured each sample into the cup and leveled the material using a flat edge across the top. This technique creates a nearly flat surface without compressing the uppermost portion of the sample. The power of the lamp was held constant to ensure that all of the samples were measured under similar thermal environments.

The ambient and SAE spectra of the simulants (Fig. 5a) highlight the complex nature of the mixtures and the spectrally dominant particle size in the simulants. The spectra of the CI Asteroid Simulant (Figs. 5a and 5b) are dominated by diagnostic spectral features indicative of phyllosilicates including the Christiansen feature (CF; an emissivity maximum that is a good indicator of bulk composition; Conel 1969) and both sets of vibration bands (also known as the reststrahlen bands or RB). Both the CF and vibration bands are consistent with ambient measurements of Orgueil. In the 1800–1200 cm⁻¹ spectral range, we also observe similarities between the CI simulant spectra and Orgueil including absorptions indicative of H₂O (e.g., Aines and Rossman 1984; Salisbury et al. 1991) and organics.

Similar to the CI Asteroid Simulant, the spectra of the CM Asteroid Simulant (Fig. 5b) are dominated by diagnostic spectral features indicative of phyllosilicates. These features are consistent with ambient measurements of Murchison and ALH 831000 (both CM chondrites;

<figure><img src="image_6.png" /></figure>

<figure><img src="image_7.png" /><figcaption>Fig. 5. Thermal emission spectra of the asteroid simulants. a) Comparison between the CI Asteroid Simulant measured at ambient conditions (dashed line) and in the simulated asteroid environment (SAE; solid line). b) Comparisons between CI, CM, and CR simulant spectra all acquired under SAE with particle sizes <75 µm. (Color figure can be viewed at wile.yonlinelibrary.com.)</figcaption></figure>

Donaldson Hanna et al. 2019). In the 1800–1200 cm⁻¹ spectral range, there are similarities between the CM simulant spectra and the CM meteorites, although these features are at slightly different frequencies in the meteorite spectra. The largest spectral differences between the CI simulant spectra and the CM simulant spectra are the 1800–1200 cm⁻¹ spectral range, where the CM simulant spectra have more subdued features.
The spectra of the CR simulant (Fig. 5b) seem to represent a more complex mixture of hydrated and anhydrous phases. The diagnostic features in the vibration band regions are similar to those in the CI and CM simulant spectra, but the shapes are wider and more subdued. The CF position is consistent with phyllosilicates, but the drop-off in emissivity at higher frequencies is less than what is observed in the CM and CI simulants. The differences in the spectral slopes in this region are likely due to the CR simulant being of coarser particle size fractions (because it contains fewer clay minerals). In the 1800–1200 cm⁻¹ spectral range, we do not observe spectral features indicative of mineral-bound H₂O and organics. In general, the CR simulant spectra are similar to MIL 090001 (CR meteorite; Donaldson Hanna et al. 2019), but the most differences are observed between the CR simulant and a CR meteorite. This is most likely due to the range of compositions observed in CR meteorites.

## Thermogravimetry and Evolved Gas Analysis

Combined thermogravimetry (TG) and evolved gas analysis (EGA) were performed at NASA Johnson Space Center Astromaterials Research and Exploration Science (ARES) laboratories to determine the volatile release patterns of the three prototype simulants. Samples were measured using a Labsys EVO differential scanning calorimeter/thermal gravimeter connected to a ThermoStar quadrupole mass spectrometer. Measurements were made under a 30-mbar helium atmosphere; this provides a neutral low-pressure environment, albeit not a high vacuum as might be present in future asteroid mining operations. Samples were heated from ambient to 1000°C at a ramp rate of 35°C min⁻¹ and a flow rate of 10 sccm He. Evolved volatile species of particular interest included H₂O (m/z = 18), C₃H₃ (m/z = 39), CO₂ (m/z = 44), and SO₂ (m/z = 64). These species are predicted to be evolved from thermal decomposition reactions of the phases in Table 2. The results—mostly the TG—can also be compared to previous TG measurements of carbonaceous chondrites (King et al. 2015), but we do not have data for all three chondrite types (CI, CM, CR) acquired with a similar instrument setup as in this work.

The TG/EGA results show that volatile release is dominated by H₂O at both high and low temperatures due to thermal decomposition reactions. Volatile release patterns for the three prototypes are shown in Fig. 6: Fig. 6a shows TG curves and integrated mass loss for all three simulant varieties (inset), while Figs. 6b–d show EGA data for key mass fragments (m/z 18 = H₂O, m/z 39 = C₃H₃, m/z 44 = CO₂, m/z 64 = SO₂). H₂O is

anticipated to be present as a physiadsorbed phase (released at low temperatures), and/or as interlayer and structural water and hydroxyl groups (released at moderate to high temperatures). High temperature H₂O release is a characteristic of dehydroxylation in phyllosilicates. C₃H₃ is a good indicator of benzene rings, tracking the thermal breakdown of the organic molecules present in the coal, analogous to meteorite IOM. CO₂ is also an anticipated decomposition product of organics, as well as a breakdown product of the siderite in the CR simulant. SO₂ may be evolved by the thermal breakdown of epomite and organics, as well as oxidation of sulfide phases. The TG curves (Fig. 6a) all show modest mass loss from ambient to ~600°C, followed by more rapid losses from 600 to 1000°C attributed to H₂O loss from dehydroxylation of phyllosilicates and decomposition of other phases. The total integrated mass loss was CI (14.3 wt%) > CM (11.2%) > CR (3.2%), which matches both the relative trends observed in the respective meteorite types, as well as the range of absolute values for these meteorites (Jarosewich 1990; Garenne et al. 2014). Previous studies using TG alone reported values >25 wt% H₂O in Orgueil (King et al. 2015); however, without supporting EGA data, it is not clear that attributing 100% of that mass loss to H₂O is reasonable. In the simulants, distinct H₂O releases are observed at both low and high temperatures (Figs. 6b–d), related to the presence of water bound in different ways as described above. A single sharp spike in the m/z 39 channel (C₃H₃) was observed around 530°C in all the simulants, attributed to the breakdown of complex organic molecules present in the coal component. The release of CO₂ showed complex patterns in all the simulants, with multiple overlapping releases between 500 and 850°C, a rise toward 1000°C, and a minor release around 400°C in the CR simulant attributed to siderite. SO₂ showed only minor releases from 450 to 900°C, with a more complex release pattern in the CI simulant which had significant epomite in the prototype recipe.

## DISCUSSION

### Mistakes and Future Updates

Mistakes were made along the development path of the asteroid simulants, and in most cases, these represented deviations from the original philosophy of sticking as closely to the meteorite mineralogy as possible. The effects of these errors became apparent in the instrumental results described above. Table 2 lists both the original mineral recipes used for the prototypes described in this work, and suggested updates for future production that more closely match the original
<figure><img src="image_8.png" /><figcaption>Fig. 6. Thermogravimetry (TG) and evolved gas analysis (EGA) from the asteroid simulants. a) TG for all three simulants; inset shows total mass loss from 0 to 1000°C. b–d) EGA for the CI, CM, and CR simulants, respectively, showing temperature-dependent release of key volatile species (same vertical scale). (Color figure can be viewed at wileyonlinelibrary.com.)</figcaption></figure>

meteorite mineralogies (Table 1). In the original mineral recipes (Table 2), the CR data from Howard et al. (2015) were interpreted as wt% when they are instead given in vol%. This resulted in modest underabundances of the dense minerals (metals, sulfides, etc.) and overabundances of the less dense minerals. We addressed this issue in the updated recipes (Table 2). Additionally, the amount of magnetite crept up during the iterative development stage to large and unreasonable concentrations. This was done in an attempt to both darken the simulants and make up for perceived Fe deficiencies, but it strayed from the original goal to make mineral-based simulants. We found that chemically produced magnetite is significantly darker than natural magnetite from mine sources, and switching the supply to chemical magnetite can help maintain low albedos typical of carbonaceous chondrites at reasonable magnetite concentrations. The updated recipes (Table 2) have significantly less magnetite, particularly in the CR simulant that was the least chemically and spectrally realistic (Table 3; Fig. 4). Another issue involved epsomite in the original CI recipe dissolving during the paste formation process, then precipitating as a white crust on the dried cobbles (Fig. 2c). While sulfates are found in carbonaceous chondrites, in some cases, these are terrestrial alteration products, and the Orgueil

mineralogy from Bland et al. (2004) did not identify crystalline sulfates. In the updated recipe, we replaced epsomite with ferrihydrite to better reproduce Bland et al.’s (2004) CI mineralogy, and to avoid issues with sulfate efflorescence.

From here on out, the lab at UCF will maintain rigorous internal versioning to track any changes in mineral recipes, or in suppliers of the source materials. In effect, the prototypes described in this work are now frozen in as “version 1.0”; when the updates from Table 2 come into effect, this will mark a new version although for simplicity and clarity, the version numbers will likely not be tacked onto the names, leaving them as “UCF CI Asteroid Simulant,” etc. We will thus discard the earlier DSI versioning scheme that used the naming convention “CM-2,” easily confused for the metamorphic grade of the meteorite (these earlier DSI prototypes were not widely distributed). Any discrepancies or questions in the future will be able to be resolved by cross-checking shipment dates with internal version tracking.

## Realism

Overall, the prototype simulants as described are mostly accurate representations of anticipated volatile-rich asteroid surface materials. In their current form,
they are appropriate for addressing scientific and engineering questions, and the simulants will be improved in the future based on updates to the mineral recipes (Table 2) and new information coming from both meteorite studies and the Hayabusa2 and OSIRIS-REx missions. In terms of quantitative metrics, Metzger et al. (2019) adopted the figure-of-merit (FoM) system developed by NASA, and they evaluated the fidelity of the CI Asteroid Simulant as an example. In this system, numerical scores are given from 0 (lowest fidelity) to 1 (highest fidelity) based on comparisons to a reference material, in this case the meteorite Orgueil and asteroid models for some properties like particle size distribution. The prototype CI simulant received high FoM scores for magnetic susceptibility (0.96), elemental chemistry (0.94), and mineralogy (0.83). FoMs for other physical properties were somewhat lower, ranging from 0.53 to 0.77. However, these still compare quite favorably to FoMs for well-known lunar simulants that score as low as 0.25–0.35 (Metzger et al. 2019). The changes to the mineral recipes in Table 2 will bring the mean mineralogy FoM for all three simulants up from 0.87 for the prototypes to 0.97 for the improved recipes. We anticipate that the fidelity of other properties will improve as a result.

## Applications

The asteroid simulants have already been delivered to researchers worldwide, and there are a variety of applications for these materials in basic science advances as well as technology maturation (e.g., Boivin et al. 2018; Fries et al. 2018). From a scientific standpoint, simulated asteroid materials can be used to investigate (1) regolith behavior in microgravity, including cohesion and sorting; (2) impact cratering processes, using simulants as a target for projectiles; (3) thermal cycling effects on asteroid material strength properties. In terms of technology development, potential applications include (1) volatile extraction using radiative energy, (2) curation protocols for future sample return of volatile-rich asteroid or comet material, (3) grappling and anchoring devices that can interact with asteroid surfaces. These are all examples of current work underway using our asteroid simulants; future applications will likely be even richer in scope and creativity.

## CONCLUSIONS

We used modal mineralogy and physical properties data from carbonaceous chondrites to create a series of simulated C-complex asteroid materials, including cobbles and regolith. Prototypes based on initial recipes were measured using a range of instrumental techniques and compared to data from reference meteorites. In

most cases, the analyses compared favorably to the references; however, there were also significant discrepancies in bulk chemistry and reflectance spectra in some cases that will be addressed in the future by updating the simulant mineral recipes. There are a wide range of applications for the asteroid simulants, and they have already seen use in diverse applications. The simulants will be distributed through the nonprofit Exolith Lab at UCF, and the mineral recipes are also published for others to use and modify as they see fit.

*Acknowledgments*—This work has been supported by NASA Award NNA14AB05A and by the NASA Solar System Exploration Research Virtual Institute. O.P. acknowledges a postdoctoral fellowship from CNES for funding. We thank an anonymous editor for their careful comments that improved the manuscript.

*Editorial Handling*—Dr. Edward Cloutis

## REFERENCES

Aines R. D., and Rossman G. R. 1984. Water in minerals? A peak in the infrared. *Journal of Geophysical Research* 89:4059–4071.

Allen C. C., Morris R. V., Jager K. M., Golden D. C., Lindstrom D. J., Lindstrom M. M., and Lockwood J. P. 1998. Martian regolith simulant JSC Mars-1 (abstract #1690). 29th Lunar and Planetary Science Conference. CD-ROM.

Barber D. J. 1981. Matrix phyllosilicates and associated minerals in C2M carbonaceous chondrites. *Geochimica et Cosmochimica Acta* 45:945–970.

Beck P. B., Maturilli A., Garenne A., Vernassa P., Helbert J., Quirico E., and Schmitt B. 2018. What is controlling the reflectance spectra (0.35-150 µm) of hydrated (and dehydrated) carbonaceous chondrites? *Icarus* 313:124–138.

Bland P. A., Cressey G., and Menzies O. N. 2004. Modal mineralogy of carbonaceous chondrites by X-ray diffraction and Mössbauer spectroscopy. *Meteoritics & Planetary Science* 39:3–16.

Boivin A. L., Hickson D., Tsai C., Cunje A., Ghent R. R., and Daly M. G. 2018. Broadband measurements of the complex permittivity of carbonaceous asteroid regolith analog materials. *Journal of Geophysical Research Planets* 123:3088–3104.

Brearley A. J. and Jones R. H. 1998. Chondritic meteorites. In *Planetary materials*, edited by Papike J. J. Albuquerque, New Mexico: Mineralogical Society of America. pp. 3-001-3-398.

Britt D. T. and Consolmagno G. J. 2003. Stony meteorite porosities and densities: A review of the data through 2001. *Meteoritics & Planetary Science* 38:1161–1180.

Bus S. J. and Binzel R. P. 2002. Phase II of the small main-belt asteroid spectroscopic survey: A feature-based taxonomy. *Icarus* 158:146–177.

Cannon K. M., Britt D. T., Smith T. M., Fritsche R. F., and Batchelder D. 2019. Mars global simulant MGS-1: A rocknest-based open standard for basaltic Martian soil simulants. *Icarus* 317:470–478.
Cheng A. F., Atchison J., Kantsiper B., Rivkin A. S., Stickle A., Reed C., Galvez A., Carnelli I., Michel P., and Ulamec S. 2015. Asteroid impact and deflection assessment mission. *Acta Astronautica* 115:262–269.

Christensen P. R., Bandfield J. L., Hamilton V. E., Howard D. A., Lane M. D., Piatek J. L., Ruff S. W., and Stefanov W. L. 2000. A thermal emission spectral library of rock-forming minerals. *Journal of Geophysical Research* 105:9735–9739.

Ciesla F. J., Lauretta D. S., Cohen B. A., and Hood L. L. 2003. A nebular origin for chondritic fine-grained phyllosilicates. *Science* 299:549–552.

Clark B. E., Hapke B., Pieters C., and Britt D. 2002. Asteroid space weathering and regolith evolution. In *Asteroids II*, edited by Binzel R. P., Gehrels T., and Matthews M. S. Tucson, Arizona: University of Arizona Press.

Cloutis E. A., Hiroi T., Gaffey M. J., Alexander C. M. D'. D., and Mann P. 2011a. Spectral reflectance properties of carbonaceous chondrites: 1 CI chondrites. *Icarus* 212:180–209.

Cloutis E. A., Hudon P., Hiroi T., Gaffey M. J., and Mann P. 2011b. Spectral reflectance properties of carbonaceous chondrites: 2. CM chondrites. *Icarus* 2016:309–346.

Cody G. D. and Alexander C. M. O'D. 2005. NMR studies of chemical structural variation of insoluble organic matter from different carbonaceous chondrite groups. *Geochimica et Cosmochimica Acta* 69:1085–1097.

Conel J. E. 1969. Infrared emissivities of silicates: Experimental results and a cloudy atmosphere model of spectral emission from condensed particulate mediums. *Journal of Geophysical Research* 74:1614–1634.

Consolmagno G. J., Britt D. T., and Macke R. J. 2008. The significance of meteorite density and porosity. *Chemie der Erde–Geochemistry* 68:1–29.

De Sanctis M. C., Ammannito E., Raponi A., Marchi S., McCord T. B., McSween H. Y., Capaccioni F., Capria M. T., Carrozzo F. G., Ciarniello M., Longobardo A., Tosi F., Fonte S., Formisano M., Frigeri A., Giardino M., Magni G., Palomba E., Turrini D., Zambon F., Combe J.-P., Feldman W., Jaumann R., McFadden L. A., Pieters C. M., Prettyman T., Toplis M., Raymond C. A., and Russell C. T. 2015. Ammoniated phyllosilicates with a likely outer Solar System origin on (1) Ceres. *Nature* 528:241–244.

Delbo M., Libourel G., Wilkerson J., Murdoch N., Michel P., Ramesh K. T., Ganino C., Verati C., and Marchi S. 2014. Thermal fatigue as the origin of regolith on small asteroids. *Nature* 508:233–236.

Donaldson Hanna K. L., Thomas I. R., Bowles N. E., Greenhagen B. T., Pieters C. M., Mustard J. F., Jackson C. R. M., and Wyatt M. B. 2012a. Laboratory emissivity measurements of the plagioclase solid solution series under varying environmental conditions. *Journal of Geophysical Research* 117:E11004.

Donaldson Hanna K. L., Wyatt M. B., Thomas I. R., Bowles N. E., Greenhagen B. T., Maturilli A., Helbert J., and Paige D. A. 2012b. Thermal infrared emissivity measurements under a simulated lunar environment: Application to the Diviner Lunar Radiometer Experiment. *Journal of Geophysical Research* 117:E00H05.

Donaldson Hanna K. L., Greenhagen B. T., Patterson III W. R., Pieters C. M., Mustard J. F., Bowles N. E., Paige D. A., Glotch T. D., and Thompson C. 2017. Effects of varying environmental conditions on emissivity spectra of bulk lunar soils: Application to Diviner thermal infrared observations of the Moon. *Icarus* 283:326–342.

Donaldson Hanna K. L., Schrader D. L., Cloutis E. A., Cody G. D., King A. J., McCoy T. J., Applin D. M., Mann J. P., Bowles N. E., Brucato J. R., Connolly Jr. H. C., Dotto E., Keller L. P., Lim L. F., Clark B. E., Hamilton V. E., Lantz C., Lauretta D. S., Russell S. S., and Schofield P. F. 2019. Spectral characterization of analog samples in anticipation of OSIRIS-REx's arrival at Bennu: A blind test study. *Icarus* 319:701–723.

Fries M., Abell P., Brisset J., Britt D., Colwell J., Dove A., Durda D., Graham L., Hartzell C., Hrovat K., John K., Karrer D., Leonard M., Love S., Morgan J., Poppin J., Rodriguez V., Sánchez-Lana P., Scheeres D., and Whizin A. 2018. The Strata-1 experiment on small body regolith segregation. *Acta Astronautica* 142:87–94.

Garenne A., Beck P., Montes-Hernandez G., Chiriac R., Toche F., Quirico E., Bonal L., and Schmitt B. 2014. The abundance and stability of “water” in type 1 and 2 carbonaceous chondrites (CI, CM and CR). *Geochimica et Cosmochimica Acta* 137:93–112.

Graps A. L., Blondel P., Bonin G., Britt D., Centuori S., Delbo M., Drube L., Duffard R., Elvis M., Faber D., Frank E., Galache J. L., Green S. F., Thimo Grundmann J., Hsieh H., Kereszturi A., Laine P., Levasseur-Regourd A.-C., Maier P., Metzger P., Michel P., Mueller M., Mueller T., Murdoch N., Parker A., Pravec P., Reddy V., Sercel J., Rivkin A., Snodgrass C., and Tanga P. 2017. ASIME 2016 white paper: In-space utilisation of asteroids: “Answers to Questions from the Asteroid Miners.” *arXiv:1612.00709v2*.

Gundlach B. and Blum J. 2013. A new method to determine the grain size of planetary regolith. *Icarus* 223:478–492.

Hayatsu R., Matsuoka S., Scott R. G., Studier M. H., and Anders E. 1977. Origin of organic matter in the early solar system–VII. The organic polymer in carbonaceous chondrites. *Geochimica et Cosmochimica Acta* 41:1325–1339.

Henderson B. G. and Jakosky B. M. 1994. Near-surface thermal gradients and their effects on mid-infrared emission spectra of planetary surfaces. *Journal of Geophysical Research* 99:19,063–19,073.

Howard K. T., Benedix G. K., Bland P. A., and Cressey G. 2009. Modal mineralogy of CM2 chondrites by X-ray diffraction (PSD-XRD). Part 1: Total pylosilicate abundance and the degree of aqueous alteration. *Geochimica et Cosmochimica Acta* 73:4576–4589.

Howard K. T., Alexander C. M. O'D., Schrader D. L., and Dyl K. A. 2015. Classification of hydrous meteorites (CR, CM and C2 ungrouped) by phyllosilicate fraction: PSD-XRD modal mineralogy and planetesimal environments. *Geochimica et Cosmochimica Acta* 149:206–222.

Jarosewich E. 1990. Chemical analyses of meteorites: A compilation of stony and iron meteorite analyses. *Meteoritics* 25:323–337.

Johnson T. V. and Fanale F. P. 1973. Optical properties of carbonaceous chondrites and their relationship to asteroids. *Journal of Geophysical Research* 78:8507–8518.

Kaplan H. H. and Milliken R. E. 2016. Reflectance spectroscopy for organic detection and quantification in clay-bearing samples: Effects of albedo, clay type, and water content. *Clays and Clay Minerals* 64:167–184.

Keil K. 2000. Thermal alteration of asteroids: Evidence from meteorites. *Planetary and Space Science* 48:887–903.
King A. J., Solomon J. R., Schofield P. F., and Russell S. S. 2015. Characterising the CI and CI-like carbonaceous chondrites using thermogravimetric analysis and infrared spectroscopy. *Earth, Planets and Space* 67:198.

Krot A. N., Hutcheon I. D., Brearley A. J., Pravdivtseva O. V., Petaev M. I., and Hohenberg C. M. 2005. Timescales and settings for alteration of chondritic meteorites. In *Meteorites and the early solar system II*, edited by Lauretta D. S. and McSween H. Y. Jr. Tucson, Arizona: University of Arizona Press. pp. 525–553.

Lauretta D. S., Al Asad M. M., Ballouz R.-L., Barnouin O. S., Bierhaus E. B., Boynton W. V., Breitenfeld L. B., Calaway M. J., Chojnacki M., Christensen P. R., Clark B. E., Connolly Jr. H. C., Drouet d'Aubigny C., Daly M. G., Daly R. T., Delbó M., DellaGiustina D. N., Dworkin J. P., Emery J. P., Enos H. L., Farnocchia D., Golish D. R., Haberle C. W., Hamilton V. E., Hergenrother C. W., Jawin E. R., Kaplan H. H., Le Corre L., McCoy T. J., McMahon J. W., Michel P., Molaro J. L., Nolan M. C., Pajola M., Palmer E., Perry M. E., Reuter D. C., Rizk B., Roberts J. J., Ryan A., Scheeres D. J., Schwartz S. R., Simon A. A., Susorney J. C. M., Walsh K. J., and Zoud X.-D., and the OSIRIS-REx team. 2019. OSIRIS-REx arrives at Asteroid (101955) Bennu: Exploration of a hydrated primitive near-Earth asteroid (abstract #2608). 50th Lunar and Planetary Science Conference. CD-ROM.

Lewis J. S. 1996. *Mining the sky: Untold riches from the asteroids, comets, and planets*. New York: Basic Books. p. 274.

Licandro J., Campins H., Kelley M., Hargrove K., Pinilla-Alonso N., Cruikshank D., Rivkin A. S., and Emery J. 2011. (65) Cybele: Detection of small silicate grains, water-ice, and organics. *Astronomy & Astrophysics* 525: A34.

Logan L. M., Hunt G. R., Salisbury J. W., and Balsamo S. R. 1973. Compositional implications of Christiansen frequency maximums for infrared remote sensing applications. *Journal of Geophysical Research* 78:4983–5003.

Macke R. J., Consolmagno G. J., and Britt D. T. 2011. Density, porosity, and magnetic susceptibility of carbonaceous chondrites. *Meteoritics & Planetary Science* 46:1842–1862.

Mackinnon I. D. R. and Zolensky M. E. 1984. Proposed structures for poorly characterized phases in C2M carbonaceous chondrite meteorites. *Nature* 309:240–242.

McKay D. S., Carter J. L., Boles W. W., Allen C. C., and Allton J. H. 1994. JSC-1: A new lunar soil simulant. *Engineering, Construction, and Operations in Space IV, American Society of Civil Engineers* 859–866.

Metzger P. T., Muscatello A., Mueller R. P., and Mantovani J. 2013. Affordable, rapid bootstrapping of the space industry and solar system civilization. *Journal of Aerospace Engineering* 26:18–29.

Metzger P. T., Britt D. T., Covey S., Schultz C., Cannon K. M., Grossman K. D., Mantovani J. G., and Mueller R. P. 2019. Measuring the fidelity of asteroid regolith and cobble simulants. *Icarus* 321:632–646.

Miyamoto H., Yano H., Scheeres D. J., Abe S., Barnouin-Jha O., Cheng A. F., Demura H., Gaskell R. W., Hirata N., Ishiguro M., Michikami T., Nakamura A. M., Nakamura R., Saito J., and Sasaki S. 2007. Regolith migration and sorting on asteroid Itokawa. *Science* 316:1011–1014.

Mueller R. P., Howe S., Kochmann D., Ali H., Andersen C., Burgoyne H., Chambers W., Clinton R., De Kestellier X., Ebelt K., Gerner S., Hofmann D., Hogstrom K., Ilves E., Jerves A., Keenan R., Keravala J., Khoshnevis B., Lim S., Metzger P., Meza L., Nakamura T., Nelson A., Partridge H., Pettit D., Pyle R., Reiners E., Shapiro A., Singer R., Tan W.-L., Vazquez N., Wilcox B., and Zelhofer A. 2016. Automated additive construction (AAC) for Earth and space using In-situ resources. Proceedings of the Fifteenth Biennial ASCE Aerospace Division International Conference on Engineering, Science, Construction, and Operations in Challenging Environments (Earth & Space 2016), American Society of Civil Engineers, Reston, Virginia, USA.

Nakamura T., Noguchi T., Tanaka M., Zolensky M. E., Kimura M., Tsuchiyama A., Nakato A., Ogami T., Ishida H., Uesugi M., Yada T., Shirai K., Fujimura A., Okazaki R., Sandford S. A., Ishibashi Y., Abe M., Okada T., Ueno M., Mukai T., Yoshikawa M., and Kawaguchi J. 2011. Itokawa dust particles: A direct link between S-type asteroids and ordinary chondrites. *Science* 333:1113–1116.

Opeil C. P., Consolmagno G. J., and Britt D. T. 2010. The thermal conductivity of meteorites: New measurements and analysis. *Icarus* 208:449–454.

Pohl L. and Britt D. T. 2017. The radiation shielding potential of CI and CM chondrites. *Advances in Space Research* 59:1473–1485.

Pohl L. and Britt D. T. 2014. Strengths of meteorites– An overview and analysis of available data. *Icarus*.

Pravdivtseva O., Krot A. N., and Hohenberg C. M. 2018. I-Xe dating of aqueous alteration in the CI chondrite Orgueil: I. Magnetite and ferromagnetic separates. *Geochimica et Cosmochimica Acta* 227:38–47.

Rivkin A. S. 2012. The fraction of hydrated C-complex asteroids in the asteroid belt from SDSS data. *Icarus* 221:744–752.

Ruff S. W., Christensen P. R., Barnera P. W., and Anderson D. L. 1997. Quantitative thermal emission spectroscopy of minerals: A laboratory technique for measurement and calibration. *Journal of Geophysical Research* 102:14,899–14,913.

Salisbury J. W., Walter L. S., Vergo N., and D'Aria D. M. 1991. Infrared (2.1-25 µm) spectra of minerals. USGS Open-File Report 87-263.

Stoeser D., Wilson S., and Rickman D. 2010. Design and specification for the Highland regolith prototype simulants NU-LHT-1M and -2M. NASA Technical Reports, TM-2010-216438.

Thomas I. R., Greenhagen B. T., Bowles N. E., Donaldson Hanna K. L., Temple J., and Calcutt S. B. 2012. A new experimental setup for making thermal emission measurements in a simulated lunar environment. *Review of Scientific Instruments* 83:124502.

Thomas I. R., Bowles N. E., Donaldson Hanna K. L., Connolly Jr. H. C., Killgore M., and Lauretta D. S. 2014. The effects of varying environmental conditions on the emissivity spectra of meteorites (abstract #1989). 45th Lunar and Planetary Science Conference. CD-ROM.

Tsuchiyama A., Mashio E., Imai Y., Noguchi T., Miura Y., Yano H., and Nakamura T. 2009. Strength measurement of carbonaceous chondrites and micrometeorites using micro compression testing machine (abstract #5189). 72nd Annual Meteoritical Society Meeting.
Tsuda Y., Yoshikawa M., Abe M., Minamino H., and Nakazawa S. 2013. System design of the Hayabusa 2-Asteroid sample return mission to 1999 JU3. *Acta Astronautica* 91:356-362.

Turcotte D. L. 1986. Fractals and fragmentation. *Journal of Geophysical Research* 91:1921–1926.

## SUPPORTING INFORMATION

Additional supporting information may be found in the online version of this article:

Vokrouhlický D., Bottke W. F., Chelsey S. R., Scheeres D. J., and Statler T. S. 2015. The Yarkovsky and YORP effects. In *Asteroids IV*, edited by Michel P., Demeo F. E., and Bottke W. F. Tucson, Arizona: The University of Arizona Press. p. 509.

**Table S1.** Sourcing information for the mineral ingredients used in the prototype asteroid simulants.