Analysis of Surface Materials by Curiosity Mars Rover - Special Collection

THE 6 AUGUST 2012 ARRIVAL OF THE CURIOSITY ROVER ON THE SURFACE
of Mars delivered the most technically advanced geochemistry labo-
ratory ever sent to the surface of another planet. Its 10 instruments
(1)* were commissioned for operations and were tested on a diverse
set of materials, including rocks, soils, and the atmosphere, during
the first 100 martian days (sols) of the mission. The five articles pre-
sented in full in the online edition of Science (www.sciencemag.org/
extra/curiosity), with abstracts in print (pp. 1476–1477), describe the
mission’s initial results, in which Curiosity’s full laboratory capabil-
ity was used.
Curiosity was sent to explore a site located in Gale crater, where
a broad diversity of materials was observed from orbit. Materials
representing interactions with aqueous environments were targeted
for study because of the emphasis on understanding habitable envi-
ronments. In addition, the mission’s
science objectives also include char-
acterizing the geologic diversity of
the landing site at all scales, including
loose surface materials such as impact
ejecta, soils, and windblown accumu-
lations of fine sediments. In certain
cases, such characterization may even
provide constraints on the evolution
of the planet as a whole. Two notable
points along Curiosity’s initial 500-m
traverse included Jake_M, a loose rock
sitting on the plains, and Rocknest, an
accumulation of windblown sand, silt,
and dust that formed in the lee of some
rocky outcrops. Sparse outcrops of lith-
ified fluvial conglomerate were also
encountered (2).
As described by Stolper et al.,
Jake_M was encountered ~282 m away
from the landing site and is a dark, mac-
roscopically homogeneous igneous rock representing a previously
unknown martian magma type. In contrast to the relatively unfraction-
ated Fe-rich and Al-poor tholeiitic basalts typical of martian igneous
rocks, it is highly alkaline and fractionated. No other known martian
rock is as compositionally similar to terrestrial igneous rocks; Jake_M
compares very closely with an uncommon terrestrial rock type known
as a mugearite, typically found on ocean islands and in rift zones. It
probably originates from magmas generated by low degrees of par-
tial melting at high pressure of possibly water-rich, chemically altered
martian mantle that is different from the sources of other known mar-
tian basalts.
Over the first 100 sols of the mission, the ChemCam instrument
returned >10,000 laser-induced breakdown spectra, helping to char-
acterize surface material diversity. ChemCam’s laser acts effectively
as a microprobe, distinguishing between fine soil grains and coarser
~1-mm grains. Based on these data, Meslin et al. report that the coarse
soil fraction contains felsic (Si- and Al-rich) grains, mimicking the
composition of larger felsic rock fragments found during the traverse
and showing that these larger components probably break apart to
form part of the soil. In contrast, the fine-grained soil component is
mafic, similar to soils observed by the Pathfinder and Mars Explora-
tion Rover missions.
Curiosity scooped, processed, and analyzed a small deposit of
windblown sand/silt/dust at Rocknest that has similar morphology and
bulk elemental composition to other aeolian deposits studied at other
Mars landing sites. Based solely on analysis of CheMin x-ray diffrac-
tion (XRD) data from Mars, calibrated with terrestrial standards, Bish
et al. estimate the Rocknest deposit to be composed of ~71% crystal-
line material of basaltic origin, in addition to ~29% x-ray–amorphous
materials. In an independent approach, Blake et al. used Alpha Par-
ticle X-ray Spectrometer data to constrain the bulk composition of the
deposit and XRD data and phase stoichiometry to constrain the chem-
istry of the crystalline component,
with the difference being attributed
to the amorphous component, result-
ing in estimates of ~55% crystalline
material of basaltic origin and ~45%
x-ray–amorphous materials. The amor-
phous component may contain nano-
phase iron oxide similar to what was
observed by earlier rovers. The similar-
ity between basaltic soils observed at
Rocknest and other Mars sites implies
either global-scale mixing of basaltic
material or similar regional-scale basal-
tic source material or some combina-
tion of both. No hydrated phases were
detected. However, as shown by Leshin
et al., pyrolysis of Rocknest fines using
the Sample Analysis at Mars (SAM)
instrument suite revealed volatile spe-
cies, probably in the amorphous com-
ponent, including H2O, SO2, CO2, and
O2, in order of decreasing abundance. ChemCam measurements of
these materials also revealed the presence of H. It is likely that H2O is
contained in the amorphous component and CO2 was liberated via the
decomposition of Fe/Mg carbonates present below the XRD detection
limit of 1 to 2%. Isotopic data from SAM indicate that this H2O, and
possibly the CO2, were derived from the atmosphere. SAM analysis
also revealed oxychloride compounds similar to those found by earlier
missions, suggesting that their accumulation reflects global planetary
processes. The evolution of CO2 during pyrolysis and the observa-
tion of simple chlorohydrocarbons during SAM gas chromatograph
mass spectrometer analyses could be consistent with organic carbon
derived from a terrestrial instrument background source, or a martian
source, either exogenous or indigenous. – JOHN P. GROTZINGER
CREDIT:NASA
Analysis of Surface Materials
by the Curiosity Mars Rover
1475www.sciencemag.org SCIENCE VOL 341 27 SEPTEMBER 2013
OVERVIEW
Curiosity used its scoop to collect two samples of a small
aeolian deposit. The deposit’s upper surface is armored by
sand grains 0.5 to 1.5 mm in size. These coarse grains are
coated with fine dust, giving the deposit an overall light
brownish red color. Beneath the coarse sand crust is finer
sand, dark brown in color. This Mars Hand Lens Imager
image was acquired on sol 84.
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena,
CA 91125, USA.
*References may be found on page 1477 after the abstracts.
10.1126/science.1244258
INTRODUCTION
Published by AAAS
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27 SEPTEMBER 2013 VOL 341 SCIENCE www.sciencemag.org
ABSTRACTS
The Petrochemistry
of Jake_M: A Martian
Mugearite
E. M. Stolper,* M. B. Baker, M. E. Newcombe, M. E. Schmidt,
A. H. Treiman, A. Cousin, M. D. Dyar, M. R. Fisk, R. Gellert, P. L. King,
L. Leshin, S. Maurice, S. M. McLennan, M. E. Minitti, G. Perrett,
S. Rowland, V. Sautter, R. C. Wiens, MSL Science Team†
*Corresponding author. E-mail: ems@gps.caltech.edu
Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena,
CA 91125, USA.
†MSL Science Team authors and affiliations are listed in the supplementary materials.
The list of author affiliations is available in the full article online.
“Jake_M,” the first rock analyzed by theAlpha
Particle X-ray Spectrometer instrument on the
Curiosity rover, differs substantially in chemi-
cal composition from other known martian
igneous rocks: It is alkaline (>15% norma-
tive nepheline) and relatively fractionated.
Jake_M is compositionally similar to terres-
trial mugearites, a rock type typically found at
ocean islands and continental rifts. By anal-
ogy with these comparable terrestrial rocks, Jake_M could have been pro-
duced by extensive fractional crystallization of a primary alkaline or transi-
tional magma at elevated pressure, with or without elevated water contents.
The discovery of Jake_M suggests that alkaline magmas may be more abun-
dant on Mars than on Earth and that Curiosity could encounter even more
fractionated alkaline rocks (for example, phonolites and trachytes).
>> Read the full article at http://dx.doi.org/10.1126/science.1239463
Soil Diversity and Hydration
as Observed by ChemCam
at Gale Crater, Mars
P.-Y. Meslin,* O. Gasnault, O. Forni, S. Schröder, A. Cousin, G. Berger,
S. M. Clegg, J. Lasue, S. Maurice, V. Sautter, S. Le Mouélic, R. C. Wiens,
C. Fabre, W. Goetz, D. Bish, N. Mangold, B. Ehlmann, N. Lanza,
A.-M. Harri, R. Anderson, E. Rampe, T. H. McConnochie, P. Pinet,
D. Blaney, R. Léveillé, D. Archer, B. Barraclough, S. Bender, D. Blake,
J. G. Blank, N. Bridges, B. C. Clark, L. DeFlores, D. Delapp, G. Dromart,
M. D. Dyar, M. Fisk, B. Gondet, J. Grotzinger, K. Herkenhoff, J. Johnson,
J.-L. Lacour, Y. Langevin, L. Leshin, E. Lewin, M. B. Madsen,
N. Melikechi, A. Mezzacappa, M. A. Mischna, J. E. Moores, H. Newsom,
A. Ollila, R. Perez, N. Renno, J.-B. Sirven, R. Tokar, M. de la Torre,
L. d’Uston, D. Vaniman, A. Yingst, MSL Science Team†
*Corresponding author. E-mail: pmeslin@irap.omp.eu
Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse, France.
CNRS, IRAP, 9 Av. Colonel Roche, BP 44346, F-31028 Toulouse cedex 4, France.
The ChemCam instrument, which
provides insight into martian soil
chemistry at the submillimeter
scale, identified two principal soil
types along the Curiosity rover
traverse: a fine-grained mafic
type and a locally derived, coarse-
grained felsic type. The mafic soil
component is representative of
widespread martian soils and is
similar in composition to the mar-
tian dust. It possesses a ubiquitous
hydrogen signature in ChemCam
spectra, corresponding to the hydration of the amorphous phases found
in the soil by the CheMin instrument. This hydration likely accounts for an
important fraction of the global hydration of the surface seen by previous
orbital measurements. ChemCam analyses did not reveal any significant
exchange of water vapor between the regolith and the atmosphere. These
observations provide constraints on the nature of the amorphous phases
and their hydration.
X-ray Diffraction Results from
Mars Science Laboratory:
Mineralogy of Rocknest at
Gale Crater
D. L. Bish,* D. F. Blake, D. T. Vaniman, S. J. Chipera, R. V. Morris,
D. W. Ming, A. H. Treiman, P. Sarrazin, S. M. Morrison, R. T. Downs,
C. N. Achilles, A. S. Yen, T. F. Bristow, J. A. Crisp, J. M. Morookian,
J. D. Farmer, E. B. Rampe, E. M. Stolper, N. Spanovich,
MSL Science Team†
*Corresponding author. E-mail: bish@indiana.edu
Department of Geological Sciences, Indiana University, Bloomington, IN 47405, USA.
The Mars Science Laboratory rover Curiosity scooped samples of soil from
the Rocknest aeolian bedform in Gale crater. Analysis of the soil with the
Chemistry and Mineralogy (CheMin) x-ray diffraction (XRD) instrument
revealed plagioclase (~An57), forsteritic olivine (~Fo62), augite, and
pigeonite, with minor K-feldspar, magnetite, quartz, anhydrite, hematite,
and ilmenite. The minor phases
are present at, or near, detection
limits. The soil also contains 27
± 14 weight percent x-ray amor-
phous material, likely containing
multiple Fe3+
- and volatile-bearing
phases, including possibly a sub-
stance resembling hisingerite. The
crystalline component is similar to
the normative mineralogy of cer-
tain basaltic rocks from Gusev cra-
ter on Mars and of martian basaltic
meteorites. The amorphous com-
Curiosity at Gale Crater
CREDITS:(LEFT)NASA;(TOPRIGHT)MESLINETAL.;(BOTTOMRIGHT)BISHETAL.
1476
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www.sciencemag.org SCIENCE VOL 341 27 SEPTEMBER 2013
ponent is similar to that found on Earth in places such as soils on the
Mauna Kea volcano, Hawaii.
Curiosity at Gale Crater,
Mars: Characterization and
Analysis of the Rocknest
Sand Shadow
D. F. Blake,* R. V. Morris, G. Kocurek, S. M. Morrison, R. T. Downs,
D. Bish, D. W. Ming, K. S. Edgett, D. Rubin, W. Goetz, M. B. Madsen,
R. Sullivan, R. Gellert, I. Campbell, A. H. Treiman, S. M. McLennan,
A. S. Yen, J. Grotzinger, D. T. Vaniman, S. J. Chipera, C. N. Achilles,
E. B. Rampe, D. Sumner, P.-Y. Meslin, S. Maurice, O. Forni, O. Gasnault,
M. Fisk, M. Schmidt, P. Mahaffy, L. A. Leshin, D. Glavin, A. Steele,
C. Freissinet, R. Navarro-González, R. A. Yingst, L. C. Kah, N. Bridges,
K. W. Lewis, T. F. Bristow, J. D. Farmer, J. A. Crisp, E. M. Stolper,
D. J. Des Marais, P. Sarrazin, MSL Science Team†
*Corresponding author. E-mail: david.blake@nasa.gov
National Aeronautics and Space Administration (NASA) Ames Research Center, Moffett Field,
CA 94035, USA.
The Rocknest aeolian deposit is similar to aeolian features analyzed by
the Mars Exploration Rovers (MERs) Spirit and Opportunity. The fraction
of sand <150 micrometers in size contains ~55% crystalline material
consistent with a basaltic heritage and ~45% x-ray amorphous material.
The amorphous component of Rocknest is iron-rich and silicon-poor and
is the host of the volatiles (water, oxygen, sulfur dioxide, carbon dioxide,
and chlorine) detected by the Sample Analysis at Mars instrument and of
the fine-grained nanophase oxide component first described from basaltic
soils analyzed by MERs. The similarity between soils and aeolian materi-
als analyzed at Gusev crater, Meridiani Planum, and Gale crater implies
locally sourced, globally similar basaltic materials or globally and region-
ally sourced basaltic components deposited locally at all three locations.
Volatile, Isotope, and Organic
Analysis of Martian Fines
with the Mars Curiosity
Rover
L. A. Leshin,* P. R. Mahaffy, C. R. Webster, M. Cabane, P. Coll,
P. G. Conrad, P. D. Archer Jr., S. K. Atreya, A. E. Brunner, A. Buch,
J. L. Eigenbrode, G. J. Flesch, H. B. Franz, C. Freissinet, D. P. Glavin,
A. C. McAdam, K. E. Miller, D. W. Ming, R. V. Morris,
R. Navarro-González, P. B. Niles, T. Owen, R. O. Pepin, S. Squyres,
A. Steele, J. C. Stern, R. E. Summons, D. Y. Sumner, B. Sutter, C. Szopa,
S. Teinturier, M. G. Trainer, J. J. Wray, J. P. Grotzinger,
MSL Science Team†
*Corresponding author. E-mail: leshin@rpi.edu
Department of Earth and Environmental Sciences and School of Science, Rensselaer
Polytechnic Institute, Troy, NY 12180, USA.
Samples from the Rocknest aeolian deposit were heated to ~835°C under
helium flow and evolved gases analyzed by Curiosity’s Sample Analysis
at Mars instrument suite. H2O, SO2, CO2, and O2 were the major gases
released. Water abundance (1.5 to 3 weight percent) and release tempera-
ture suggest that H2O is bound within an amorphous component of the
sample. Decomposition of fine-grained Fe or Mg carbonate is the likely
source of much of the evolved CO2. Evolved O2 is coincident with the release
of Cl, suggesting that oxygen is produced from thermal decomposition of
an oxychloride compound. Elevated δD values are consistent with recent
atmospheric exchange. Carbon isotopes indicate multiple carbon sources
in the fines. Several simple organic compounds were detected, but they are
not definitively martian in origin.
OVERVIEW
References
1. J. P. Grotzinger et al., Mars Science Laboratory mission and science investigation. Space Sci.
Rev. 170, 5 (2012).
2. R. M. E. Williams et al., Martian fluvial conglomerates at Gale crater. Science 340, 1068
(2013).
See all of Science’s Curiosity coverage,
including news, research, and multimedia,
at www.sciencemag.org/extra/curiosity
CREDITS:(LEFT)NASA;(RIGHT)NASA
1477
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DOI: 10.1126/science.1239505
, (2013);341Science
et al.D. F. Blake
Rocknest Sand Shadow
Curiosity at Gale Crater, Mars: Characterization and Analysis of the
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Curiosity at Gale Crater, Mars:
Characterization and Analysis
of the Rocknest Sand Shadow
D. F. Blake,1
* R. V. Morris,2
G. Kocurek,3
S. M. Morrison,4
R. T. Downs,4
D. Bish,5
D. W. Ming,2
K. S. Edgett,6
D. Rubin,7
† W. Goetz,8
M. B. Madsen,9
R. Sullivan,10
R. Gellert,11
I. Campbell,11
A. H. Treiman,12
S. M. McLennan,13
A. S. Yen,14
J. Grotzinger,15
D. T. Vaniman,16
S. J. Chipera,17
C. N. Achilles,2
E. B. Rampe,2
D. Sumner,18
P.-Y. Meslin,19
S. Maurice,19
O. Forni,19
O. Gasnault,19
M. Fisk,20
M. Schmidt,21
P. Mahaffy,22
L. A. Leshin,23
D. Glavin,22
A. Steele,24
C. Freissinet,22
R. Navarro-González,25
R. A. Yingst,16
L. C. Kah,26
N. Bridges,27
K. W. Lewis,28
T. F. Bristow,1
J. D. Farmer,29
J. A. Crisp,14
E. M. Stolper,15
D. J. Des Marais,1
P. Sarrazin,30
MSL Science Team‡
The Rocknest aeolian deposit is similar to aeolian features analyzed by the Mars Exploration
Rovers (MERs) Spirit and Opportunity. The fraction of sand <150 micrometers in size contains
~55% crystalline material consistent with a basaltic heritage and ~45% x-ray amorphous material.
The amorphous component of Rocknest is iron-rich and silicon-poor and is the host of the volatiles
(water, oxygen, sulfur dioxide, carbon dioxide, and chlorine) detected by the Sample Analysis at
Mars instrument and of the fine-grained nanophase oxide component first described from
basaltic soils analyzed by MERs. The similarity between soils and aeolian materials analyzed at
Gusev Crater, Meridiani Planum, and Gale Crater implies locally sourced, globally similar
basaltic materials or globally and regionally sourced basaltic components deposited locally at
all three locations.
T
he Mars Science Laboratory (MSL) rover
Curiosity began exploring the surface of
Mars on 6 August 2012 (universal time co-
ordinated); until 13 September 2012, it conducted
an initial engineering checkout of its mobility sys-
tem, arm, and science instruments. Curiosity spent
sols 57 to 100 (1) at a location named Rocknest,
collecting and processing five scoops of loose, un-
consolidated materials extracted from an aeolian
sand shadow (2).
Five scoops of material from the Rocknest
sand shadow were individually collected and
sieved (<150 mm) by the Sample Acquisition,
Sample Processing and Handling–Collection
and Handling for In situ Martian Rock Analysis
(SA/SPaH-CHIMRA) instrument (3). Scoops 1 and
2 were processed by CHIMRA and discarded
to reduce (by entrainment and dilution) any ter-
restrial organic contamination that may have
remained after a thorough cleaning on Earth (4)
and to coat and passivate the interior surfaces of
the collection device with Mars dust. Portions
(40 to 50 mg) of scoops 3 and 4 were delivered
to the Chemistry and Mineralogy (CheMin) in-
strument (5) and the “observation tray,” a 7.5-cm-
diameter flat Ti-metal surface used for imaging
and analyzing scooped and sieved material with
Curiosity’s arm and mast instruments. Portions of
scoop 5 were delivered to both CheMin and the
Sample Analysis at Mars (SAM) quadrupole mass
spectrometer/gas chromatograph/tunable laser
spectrometer suite of instruments (6).
We describe the physical sedimentology of
Rocknest and suggest possible sources for the
material making up the sand shadow. We use
Alpha-Particle X-ray Spectrometer (APXS) and
CheMin data to determine the amounts and chem-
istry of the crystalline and amorphous components
of the sand shadow and compare these results with
global soil measurements from the Mars Explora-
tion Rovers (MERs) and to basaltic martian mete-
orites analyzed on Earth.
Results
Description and Interpretation of the
Rocknest Sand Shadow
The Rocknest sand shadow (7) is an accumula-
tion of wind-blown sediment deposited in the
lower-velocity lee of an obstacle in the path of
the wind. The orientation of the sand shadow in-
dicates that the constructive winds were from the
north. The surface is composed of dust-coated,
predominantly rounded, very coarse (1- to 2-mm)
sand grains (Fig. 1A). Trenches created during
the scooping show that these larger grains form
an armored surface ~2 to 3 mm in thickness (Fig.
1B). Beneath the armored surface, the bedform
interior consists of finer-grained material whose
size distribution extends through the resolution
limit of Mars Hand Lens Imager (MAHLI) im-
ages (~30 mm per pixel under the conditions of the
observation) (8). Because of CHIMRA’s 150-mm
sieve, the larger grains that armor the surface
could not be analyzed by CheMin.
Coarse sand grains that fell from the crust
into the scoop-troughs lost their dust coating
and show diversity in color, luster, and shape.
Among the grains are gray and red lithic frag-
ments, clear/translucent crystal fragments, and
spheroids with glassy luster (Fig. 1C). Some grains
showed bright glints in the martian sunlight,
suggesting specular reflections from mineral crys-
tal faces or cleavage surfaces [similar features
were observed by the optical microscope on board
the Mars Phoenix Lander (9)]. MAHLI images
of a sieved portion of material deposited on the
observation tray (3) showed a variety of particle
types from clear to colored to dark, angular to
spherical, and dull to glassy-lustered (Fig. 1D).
During the scooping process, fragments of the
armored surface were cohesive to the extent that
“rafts” of surface crust were laterally compressed
and displaced forward, and fragments of the crust
fell into the scoop hole as cohesive units (Fig. 1B).
The surface crust was also fractured and broken
into rafts during scuffing by rover wheels (a pro-
cess by which an excavation is made into the sub-
surface of unconsolidated regolith by rotating a
single rover wheel). Material beneath the crust
also had some cohesion, as shown by the over-
steep walls of the scoop scars (much greater than
the angle of repose and vertical in some cases).
The sand shadow has a discernible internal
structure. On the headwall and flanks of each
scoop trench, a lighter-tone layer is apparent
~1 cm beneath and parallel to the dune surface
(Fig. 1B). The origin of the layering is not un-
derstood, and three hypotheses are viable. First,
RESEARCH ARTICLE
1
National Aeronautics and Space Administration (NASA) Ames
Research Center, Moffett Field, CA 94035, USA. 2
NASA Johnson
Space Center, Houston, TX 77058, USA. 3
Department of Geolog-
ical Sciences, University of Texas, Austin, TX 78712, USA. 4
Depart-
ment of Geology, University of Arizona, Tucson, AZ 85721,
USA. 5
Department of Geological Sciences, Indiana University,
Bloomington, IN 47405, USA. 6
Malin Space Science Systems,
San Diego, CA 92191, USA. 7
U.S. Geological Survey, Santa Cruz,
CA 95060, USA. 8
Max-Planck-Institut für Sonnensystemforschung,
37191 Katlenburg-Lindau, Germany. 9
Niels Bohr Institute,
University of Copenhagen, 2100 Copenhagen, Denmark. 10
Center
forRadiophysicsandSpaceResearch,CornellUniversity,Ithaca,NY
14850, USA. 11
University of Guelf, Guelph, Ontario, N1G2W1,
Canada.12
LunarandPlanetaryInstitute,Houston,TX77058,USA.
13
State University of New York–Stony Brook, Stony Brook, NY
11790, USA. 14
Jet Propulsion Laboratory/California Institute of
Technology, Pasadena, CA 91109, USA. 15
California Institute of
Technology, Pasadena, CA 91125, USA. 16
Planetary Science
Institute,Tucson,AZ85719,USA.17
ChesapeakeEnergy,Oklahoma
City, OK 73102, USA. 18
University of California, Davis, CA 95616,
USA. 19
Institut de Recherche en Astrophysique et Planétologie
(IRAP), UPS-OMP-CNRS, 31028 Toulouse, France. 20
Oregon State
University, Corvallis, OR 97331, USA. 21
Finnish Meteorological
Institute, Fl-00101 Helsinki, Finland. 22
NASA Goddard Space
Flight Center, Greenbelt, MD 20771, USA. 23
Rensselaer Poly-
technic Institute, Troy, NY 12180, USA. 24
Geophysical Laboratory,
Carnegie Institution of Washington, Washington, DC 20015, USA.
25
University Nacional Autonóma de México, Ciudad Universitaria,
04510 México D.F. 04510, Mexico. 26
Department of Earth and
Planetary Sciences, University of Tennessee, Knoxville, TN 37996,
USA. 27
The Johns Hopkins University Applied Physics Labora-
tory, Laurel, MD 20723, USA. 28
Princeton University, Princeton,
NJ 08544, USA. 29
Arizona State University, Phoenix, AZ 85004,
USA. 30
SETI Institute, Mountain View, CA 94043, USA.
*Corresponding author. E-mail: david.blake@nasa.gov
†Present address: Department of Earth and Planetary Sciences,
University of California, Santa Cruz, CA 95064, USA.
‡MSL Science Team authors and affiliations are listed in the
supplementary materials.
www.sciencemag.org SCIENCE VOL 341 27 SEPTEMBER 2013 1239505-1

the layering may represent changes in bulk com-
position or grain size that occurred during dep-
osition. Second, the layering may be the result
of changes in oxidation state or other chemical
properties that occurred after deposition, in which
case the conformable nature of the banding and
the surface of the sand shadow reflect depth-
dependent postdepositional chemical processes.
Finally, the layering may represent zones richer
or poorer in light-toned dust, reflecting times of
lesser or greater sand accumulation relative to
the air-fall dust.
The aeolian bedform at Rocknest is quite sim-
ilar to coarse-grained ripples encountered at Gusev
by the MER Spirit (10, 11) and at Meridiani
Planum by the MER Opportunity (12, 13) in that
a coarse-grained, indurated, dust-coated surface
overlies an interior of markedly finer sediment.
Coarse-grained ripples on Earth typically consist
of a surface veneer of coarse grains and a finer-
grained interior (7, 14), and the martian bed-
forms have been considered analogous features
(13, 15). The spatial grain-size sorting within
coarse-grained ripples is thought to arise because
of the short grain excursion length of the coarse
grains traveling in creep and the much longer ex-
cursion length of finer saltating grains (16). With
ripple migration,coarse grains are recycled through
the bedform and become concentrated on the
ripple surface, where impacts from saltating grains
tend to buoy the grains upward.
Although the dynamics of sand shadows dif-
fer from those of coarse-grained ripples, and sand
shadows on Earth do not characteristically show
a coarse-grained surface, similar dynamics may
arise owing to the mix-load transport of grains in
creep and saltation. Alternate interpretations are
also possible. First, the coarse-grained surface
could represent a lag formed as winds deflated
finer grains. However, the paucity of coarse grains
within the interior indicates that an unreasonable
amount of deflation would have had to occur to
produce the veneer. Second, the coarse-grained
veneer could represent the terminal growth phase
of the bedform. Because the size of a sand shad-
ow is fixed by the upwind obstacle size (17),
once the terminal size is approached, the lower
wind speeds that characterize the wake and allow
for deposition of finer sediment are replaced by
wind speeds that approach the unmodified (pri-
mary) winds. At this point, there would be se-
lective deposition of coarse grains traveling in
creep, whereas finer saltating grains would by-
pass the bedform. Third, the sand shadow could
have formed largely by the more readily trans-
ported fine saltation load, but as the area became
depleted in finer grains, more of the residuum of
Fig. 1. The Rocknest sand shadow, where Cu-
riosity spent sols 57 to 100 conducting engi-
neering tests and science observations of the
material. (A) Mosaic of 55 MAHLI images show-
ing Curiosity parked on the east side of the Rocknest
sand shadow during the sampling campaign on sol
84. The location of each of the five scoops is indi-
cated. The inset is a portion of Mars Reconnaissance
Orbiter High Resolution Imaging Science Experiment
image ESP_028678_1755 showing the Rocknest
sand shadow as seen from about 282 km above
the ground. (B) MAHLI image of third scoop trench,
showing the dust-coated, indurated, armoring layer
of coarse and very coarse sand and underlying darker
finer sediment. (C) MAHLI image of Rocknest sand
shadow surface disrupted by the rover’s front left
wheel on sol 57. The larger grains came from the
armoring layer of coarse sand on the sand shadow
surface. (D) MAHLI image of a <150-mm sieved por-
tion from the third scoop; grains similar to those
delivered to the CheMin and SAM instruments, de-
livered to Curiosity’s Ti observation tray.
27 SEPTEMBER 2013 VOL 341 SCIENCE www.sciencemag.org1239505-2

coarser grains would be incorporated into trans-
port, with the coarse-grained surface arising through
subsequent deflation.
None of these interpretations explains the gen-
eral absence of observed coarse grains in the in-
terior; the contrast in grain size between the surface
and the interior is more marked in the Rocknest
sand shadow and in some of the coarse-grained
ripples observed by MERs than in many Earth
examples. This may reflect the greater impact en-
ergy of saltating grains on Mars compared with
Earth and their ability to transport dispropor-
tionally larger grains in creep (18). Regarding the
apparent absence of interior coarse grains, the small
scooped areas may not be representative of the en-
tire bedform, and interior horizons of coarse grains
could easily have been bypassed. In addition, as seen
with coarse-grained ripples on Earth, the amount of
coarse sediment occurring in the interior varies
and decreases with the supply of coarse grains.
Regardless of the origin of the coarse-grained
surface, this armored surface would stabilize
the bedform during all but the strongest wind
events. In turn, the armored surface would allow
time for surface induration to develop, further sta-
bilizing the sand shadow. The similarity of the
armoring and induration of the sand shadow at
Rocknest to coarse-grained ripples encountered
by Spirit and Opportunity suggests that the pro-
cesses of grain transport and stabilization are
similar across equatorial Mars and that Mars’
winds (in recent eras) rarely were strong enough
to transport sand grains of 1- to 3-mm diam-
eter. To move the grains at the current atmo-
spheric pressure of 0.02 kg/m3
, the wind velocities
would need to be ~36 m/s (80 mph) and ~52 m/s
(116 mph), with and without saltation, respec-
tively. Under conditions of high obliquity, dur-
ing which time the atmospheric pressure could
increase to 0.04 kg/m3
, these values would de-
crease to 26 m/s (58 mph) and ~37 m/s (83 mph),
respectively (see Materials and Methods). The
potential antiquity of the Rocknest sand shadow
is highlighted by comparing it with granule ripples
on Meridiani Planum, where cratering postdates a
field of pristine granule ripples and the crater count
suggests an age of 50,000 to 200,000 years (19).
Mineralogy of the Rocknest Sand Shadow
Analysis and interpretation of the mineralogy of
the Rocknest sand shadow is given in Bish et al.
(20). Rocknest consists of both crystalline and
x-ray amorphous components. The crystalline
component is basaltic, composed of plagioclase
feldspar, forsteritic olivine, and the pyroxenes
augite and pigeonite (20). All of the minor phases
are consistent with a basaltic heritage, with the
exception of anhydrite and hematite. By constrain-
ing the compositions of the individual crystalline
phases on the basis of their measured unit-cell
parameters, the chemical compositions of the
minerals of Rocknest were determined (21, 22).
The crystalline component of Rocknest is
chemically and mineralogically similar to that
inferred for martian basalts across the planet
and many of the basalts found in martian me-
teorites (Table 1) and, apart from somewhat
lower Fe and K, broadly similar to estimates of
the average martian crust (23). These basalts all
contain (or have chemical compositions consist-
ent with) the minerals olivine, augite, pigeonite,
and plagioclase feldspar. The mineral propor-
tions of the crystalline component of Rocknest
are virtually identical to those calculated for the
unaltered Adirondack class basalts from Gusev
Crater (CIPW normative mineralogy from their
APXS analyses) (Table 1) (24, 25). Chemically,
the mafic minerals of the Rocknest sediment (oli-
vine, augite, and pigeonite) are all consistent with
high-temperature chemical equilibria among Ca,
Fe, and Mg at 1050 T 75°C (Fig. 2). This con-
sistency with chemical equilibria suggests, but
does not prove, that these minerals and the plagio-
clase feldspar all derived from a common basaltic
source rock, which was broken down into indi-
vidual grains or lithic fragments and transported
to Rocknest from regional source areas.
Bulk Chemistry of the Rocknest
Sand Shadow
APXS provided an independent means of deter-
mining bulk chemistry of material in the Rock-
nest sand shadow. A measurement was made in
a wheel scuff named Portage, which was largely
devoid of surface crust (Fig. 1A). The chemical
composition (taking into account analytical un-
certainty) is within 2 SD of MER APXS analyses
of basaltic soils (Table 2). The APXS chem-
istry of basaltic soils analyzed by the MERs at
Gusev Crater and Meridiani Planum landing sites
(Table 2) are within 1 SD of each other except
for MgO and Na2O, which are the same within
2 SD (24–28). The MER compositional averages
exclude soils that contain a substantial local com-
ponent (high SO3 and high SiO2 for Gusev and
high Fe2O3 for Meridiani). The near identity of
compositions of the Rocknest, Gusev, and Merid-
ian basaltic soils implies either global-scale mix-
ing of basaltic material or similar regional-scale
basaltic source material or some combination
thereof.
Table 1. Mineralogy of Rocknest soil [CheMin x-ray diffraction (XRD)]
and normative mineralogies of basaltic materials from Gusev Crater
and of martian meteorites. (Rocknest data are amorphous-free values.)
Rocknest soil by CheMin (20), average of scoop 5, proportions of crystalline
phases normalized to 100%; values in italics uncertain. CIPW norms (weight) for
Gusev basaltic materials from MER APXS chemical analyses (26), ignoring S and
Cl; Fe3+
/Fetot for Backstay and Irvine taken as 0.17, the value for an Adirondack
basalt surface ground flat with the MER Rotary Abrasion Tool (RAT) (26). CIPW
norms (wt %) of martian meteorites from bulk compositions; Fe3+
/Fetot as
analyzed for Shergotty and Elephant Moraine (EETA) 79001A, estimated at
0.1 for Northwest Africa (NWA) 6234 and 0 for Queen Alexandra Range (QUE)
94201. K-spar is sanidine for the Rocknest soil, and normative orthoclase for
others. Low-Ca Pyx is pigeonite for the soil and normative hypersthene for
others. High-Ca Pyx is augite for the soil and normative diopside for others.
Fe-Cr oxide includes magnetite, hematite, and chromite. All phosphorus in
analyses are calculated as normative apatite. Mg no. is the % magnesium
substituting for iron in the olivine structure, An refers to the % Ca substituting
for Na in the plagioclase structure.
Location Gale Gusev Meteorites
Sample
Rocknest
sand shadow
Adirondack Backstay Irvine Shergotty
NWA
6234
EETA
79001A
QUE 94210
Quartz 1.4 0 0 0 0.2 0 0 3
Plagioclase 40.8 39 49 32 23 19 19 32
K-spar 1.3 1 6 6 1 0.5 0 0
Low-Ca Pyx 13.9 15 14 21 46 30 47 15
High-Ca Pyx 14.6 15 5 13 25 16 16 38
Olivine 22.4 20 15 16 0 27 13 0
Fe-Cr oxides 3.2 6 4 6 3 4 2 0
Ilmenite 0.9 1 2 2 2 2 1 4
Apatite – 1 3 2 2 2 1 6
Anhydrite 1.5
Mg no. 61 T 3 57 62 55 51 63 63 40
An 57 T 3 42 29 19 51 50 60 62
RESEARCH ARTICLE

In contrast to the APXS measurement at
the Portage wheel scuff, both CheMin and SAM
measurements were carried out on the sieved,
<150-mm-size fraction of soil. To discriminate
potential differences between the fines deliv-
ered to CheMin and SAM and the bulk material
analyzed in the wheel scuff, APXS chemistry
was obtained from portions of sieved material
deposited on the observation tray. APXS spectra
from the bulk and sieved material are nearly iden-
tical, with the exception of a prominent Ti peak
and increased background from the observation
tray (reflecting Ti metal of the tray). Addition-
ally, Ca, Mn, and Fe signals in spectra from the
observation tray are lowered proportionally as
a function of their atomic number, which sug-
gests that a fraction of these grains is smaller
than the APXS sampling depth (29). Slightly ele-
vated S and Cl, with a S/Cl ratio similar to that
found in soils by MERs (30), suggest a potential
enrichment of these two elements in the <150-mm
fraction delivered to the observation tray.
To determine the amount and composition
of the amorphous component, mass balance cal-
culations were performed using the chemical
composition of the bulk sample, the chemical
compositions of the individual phases (e.g., pla-
gioclase, sanidine, and olivine) and the relative
proportions of those phases in the crystalline
component. The empirical formulas of the major
crystalline phases (Table 3) and their chemical
compositions (table S2) were calculated from
cell parameter data (20, 21) (table S1). The chem-
ical formulas and compositions of the minor
crystalline components were assigned by stoi-
chiometry (e.g., ilmenite as TiFeO3). The rela-
tive proportions of amorphous and crystalline
components and their respective bulk compo-
sitions are summarized in Table 4, with Rocknest
having ~45 weight percent (wt %) amorphous
and ~55 wt % crystalline components (31). The
chemical compositions and proportions of amor-
phous and crystalline components were calculated
on a light-element–free basis. The relative propor-
tion of the amorphous component will in reality
be greater than 45 wt % because the volatile in-
ventory is associated with that component (32).
Abundance estimates for the x-ray amorphous
component of a sample may vary considerably,
depending on the method used for their determi-
nation. Bish et al. (20), for example, used a full
pattern-fitting method together with known amor-
phous standard materials analyzed in the labo-
ratory to determine the amount of amorphous
or poorly crystalline material contained in the
CheMin x-ray diffraction pattern. Their reported
value of ~27 wt % T 50% (1 SD range of 13 to
40 wt %), as calculated from diffraction and
scattering data alone, is somewhat lower than
the ~45% calculated from mass balance consid-
erations, but both values are within the combined
analytical uncertainty of the two techniques.
The inferred chemical composition of the amor-
phous component (Table 4) contains ~23% FeO +
Fe2O3, suggesting that ferric nanophase oxide
[npOx (25, 26, 33)] is present in abundance.
Similarly, S (principally contained within the amor-
phous component) is closely associated with the
npOx in dunes at the MER sites (24, 27) as well.
Abundances of SO3 and Cl are correlated in soils
from Gusev and Meridiani, which implies that
both are associated with npOx in the amorphous
component because these elements are not asso-
ciated with Mg, Ca, or Fe in crystalline phases.
The elements Cr, Mn, and P were associated
with the amorphous component (Table 4), but
Table 2. Basaltic soil compositions from APXS analyses for Rocknest Portage, Gusev Crater,
and Meridiani Planum.
Rocknest Gusev Meridiani
Number 1* 48†
29†
SiO2 (wt %) 42.88 T 0.47 46.1 T 0.9 45.7 T 1.3
TiO2 1.19 T 0.03 0.88 T 0.19 1.03 T 0.12
Al2O3 9.43 T 0.14 10.19 T 0.69 9.25 T 0.50
Cr2O3 0.49 T 0.02 0.33 T 0.07 0.41 T 0.06
Fe2O3 + FeO 19.19 T 0.12 16.3 T 1.1 18.8 T 1.2
MnO 0.41 T 0.01 0.32 T 0.03 0.37 T 0.02
MgO 8.69 T 0.14 8.67 T 0.60 7.38 T 0.29
CaO 7.28 T 0.07 6.30 T 0.29 6.93 T 0.32
Na2O 2.72 T 0.10 3.01 T 0.30 2.21 T 0.18
K2O 0.49 T 0.01 0.44 T 0.07 0.48 T 0.05
P2O5 0.94 T 0.03 0.91 T 0.31 0.84 T 0.06
SO3 5.45 T 0.10 5.78 T 1.25 5.83 T 1.04
Cl 0.69 T 0.02 0.70 T 0.16 0.65 T 0.09
Br (mg/g) 26 T 6 53 T 46 100 T 111
Ni 446 T 29 476 T 142 457 T 97
Zn 337 T 17 270 T 90 309 T 87
Sum (wt %) 99.85 99.88 99.88
Cl/SO3 0.13 T 0.02 0.12 T 0.02 0.11 T 0.01
*Gellert et al., 2013 (35); analytical uncertainty. †T1SD of average.
Table 3. Empirical chemical formulas of the four
major phases identified in the Rocknest soil
estimated by crystal-chemical techniques.
Phase Formula
Olivine (Mg0.62(3)Fe0.38)2SiO4
Plagioclase (Ca0.57(13)Na0.43)(Al1.57Si2.43)O8
Augite (Ca0.75(4)Mg0.88(10)Fe0.37)Si2O6
Pigeonite (Mg1.13(9)Fe0.68(10)Ca0.19)Si2O6
Fig. 2. Pyroxene compositional quadrilateral, showing the chemical and thermal relations be-
tween the major igneous minerals in the Rocknest sand shadow. Compositions of augite, pigeonite,
and olivine in the Rocknest dune material, plotted on the pyroxene quadrilateral. En, enstatite, Mg2Si2O6;
Di, diopside, CaMgSi2O6; Hd, hedenbergite, CaFeSi2O6; and Fs, ferrosilite, Fe2Si2O6. Pyroxenes are plotted
within the quadrangle, based on CheMin XRD unit-cell parameters; olivine is plotted below the quad-
rilateral at the appropriate molar Mg/Fe ratio (20). Ellipses for each mineral approximate the uncer-
tainties in mineral compositions from their unit-cell parameters. Gray background lines represent the
surface of the pyroxene solvus, with temperatures in °C (40). Red lines are approximate equilibrium tie
lines from the augite centroid composition to compositions of olivine and pigeonite, based on similar
tie lines in an equilibrated anorthosite in lunar sample 62236 (41).

they could instead be present as crystalline phases
(e.g., Ca-phosphate and chromite) at abundances
below the CheMin detection limit and/or as sub-
stitutional impurities in the major crystalline phases
(e.g., Mn and Cr in pyroxene).
The SAM instrument analyzed Rocknest for
volatile species and organic molecules (32), and
it detected, in order of decreasing abundance,
H2O, SO2, CO2, and O2. The crystalline phases,
aside from a minor anhydrite component, do not
include these species as a part of their structure,
so they must either be present in the amorphous
component or be present in the crystalline com-
ponent at levels below the XRD detection limit,
or both.
ChemCam spot observations in the scoop
walls of Rocknest are characterized by the strong
emissions from elemental hydrogen, although
ChemCam is not sensitive to its bonding state (34).
Comparison of this result with those of CheMin
and SAM suggests that ChemCam detections
of hydrogen most likely correspond to the H2O
associated with the amorphous component de-
tected by CheMin.
Discussion
Global, Regional, and Local Sources
The crystalline phases in the Rocknest fines are
consistent with a basaltic source and fit well
within the measured qualitative mineralogy of
basaltic martian meteorites and the normative
mineralogy of Adirondack class olivine basalts
at Gusev Crater (25) (Table 1). If the Rocknest
assemblage of basaltic crystalline and amorphous
components is locally derived, it is distinct from
mafic float rocks analyzed to date by APXS and
ChemCam in Gale Crater (34, 35). This obser-
vation suggests that the similarity in the chem-
ical compositions of aeolian bedforms (basaltic
soil) at Gale, Gusev, and Meridiani (Table 2)
might result from global-scale aeolian mixing
of local-to-regional basaltic material that may
or may not have variable chemical composi-
tions. This process would require sufficiently
strong winds occurring with sufficient frequen-
cy over a long enough time to achieve global or
regional-scale transport of grains by saltation and
suspension.
An alternative explanation for the compara-
ble chemical compositions of aeolian bedforms
at Gale, Gusev, and Meridiani is that the chem-
ical compositions of martian basalts are similar
at regional scales everywhere on the planet. The
Rocknest sand shadow could reasonably have
locally sourced 1- to 2-mm particles, with finer-
grained regional basaltic material plus a contri-
bution from global dust. The similarity of soil
compositions (Table 2) suggests that the basaltic
fine-grained materials at Gusev, Meridiani, and
Gale Crater provide a reasonable approximation
to the bulk composition of the exposed martian
crust (36, 37).
It is tempting to suggest that the light-toned
martian dust is largely represented by the Rocknest
amorphous component. However, we have no
data to show that the <150-mm size fraction (clay
to fine-sand size fraction) of material analyzed
by CheMin has its finest material preferential-
ly enriched in amorphous material. The evi-
dence from MER for basaltic soils suggests that
the chemical composition of the fine-grained,
light-toned soil is approximately the same as the
coarser-grained, dark-toned soils [e.g., table 10
in (38)].
The central mound of Gale Crater (Mt. Sharp
or Aeolis Mons) exhibits reflectance spectra sug-
gesting the presence of crystalline hydrated sul-
fate minerals and phyllosilicates (39), but neither
was seen in Rocknest (above the 1 to 2% level).
The absence of material from Mt. Sharp could
arise from the wind pattern during formation
of the Rocknest sand shadow; it is oriented so
as to imply sediment transport from the north,
and Mt. Sharp is east and southeast of Rocknest.
Materials and Methods
Calculation of Wind Speeds Required
to Form the Rocknest Sand Shadow
The wind velocity required to move the coarse
grains of the sand shadow by creep can be cal-
culated. The critical shear velocity (u*c) of the
wind needed to transport 1-mm-diameter (d) grains
is given by (42) as
u*c ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
0:0123 sgd þ
0:0003 kg=s2
ñf d
!v
u
u
t
where s ¼ ñs=ñf , ñs is the density of the grains
using basalt (3000 kg/m3
), ñf is the density of
Table 4. Chemical composition and proportion of XRD amorphous component in Rocknest Portage from APXS and CheMin data.
Origin Remove XRD crystalline component* Composition
APXS† APXS+
CheMin
Plagio-
clase
San-
idine
Olivine Augite
Pigeon-
ite
Ilmen-
ite
Hema-
tite
Mag-
netite
Anhy-
drite
Quartz
Amor-
phous‡
Crystal-
line
SiO2, wt % 42.88 42.88 30.88 30.42 25.95 21.63 17.51 17.51 17.51 17.51 17.51 16.76 37.20 47.59
TiO2 1.19 1.19 1.19 1.19 1.19 1.19 1.19 0.93 0.93 0.93 0.93 0.93 2.06 0.47
Al2O3 9.43 9.43 2.85 2.72 2.72 2.72 2.72 2.72 2.72 2.72 2.72 2.72 6.04 12.24
Cr2O3 0.49 0.49 0.49 0.49 0.49 0.49 0.49 0.49 0.49 0.49 0.49 0.49 1.09 0.00
FeO+Fe2O3
§
19.19 10.43 10.43 10.43 10.43 10.43 10.43 10.43 10.43 10.43 10.43 10.43 23.14 -0.10
FeO-Cryst||
— 7.37 7.37 7.37 3.31 2.29 0.59 0.35 0.35 0.00 0.00 0.00 -0.01 13.48
Fe2O3-Cryst¶
— 1.39 1.39 1.39 1.39 1.39 1.39 1.39 0.79 0.00 0.00 0.00 -0.01 2.55
MnO 0.41 0.41 0.41 0.41 0.41 0.41 0.41 0.41 0.41 0.41 0.41 0.41 0.91 0.00
MgO 8.69 8.69 8.69 8.69 4.97 3.72 2.19 2.19 2.19 2.19 2.19 2.19 4.86 11.86
CaO 7.28 7.28 4.65 4.65 4.65 3.19 2.87 2.87 2.87 2.87 2.53 2.53 5.61 8.67
Na2O 2.72 2.72 1.62 1.60 1.60 1.60 1.60 1.60 1.60 1.60 1.60 1.60 3.56 2.03
K2O 0.49 0.49 0.49 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.40 0.89 0.16
P2O5 0.94 0.94 0.94 0.94 0.94 0.94 0.94 0.94 0.94 0.94 0.94 0.94 2.09 -0.01
SO3 5.45 4.96 4.96 4.96 4.96 4.96 4.96 4.96 4.96 4.96 4.96 4.96 11.01 -0.05
SO3-Cryst#
— 0.49 0.49 0.49 0.49 0.49 0.49 0.49 0.49 0.49 0.00 0.00 -0.01 0.90
Cl 0.61 0.61 0.61 0.61 0.61 0.61 0.61 0.61 0.61 0.61 0.61 0.61 1.35 -0.01
Sum 99.77 99.77 77.47 76.77 64.52 56.47 48.80 48.30 47.70 46.55 45.71 44.96 99.77 99.77
∑(FeO+Fe2O3) 19.19 19.19 — — — — — — — — — — 23.14 16.03
∑(SO3) 5.54 5.54 — — — — — — — — — — 11.01 0.90
Relative to whole sample 22.3 0.7 12.3 8.0 7.6 0.5 0.6 1.2 0.8 0.8 45.3 54.7
Relative to XRD crystalline 40.8 1.3 22.4 14.6 13.9 0.9 1.1 2.1 1.5 1.4 — 100.0
*Plagioclase, An57; Olivine, Fo62; Augite, En44Fs20Wo36 (Mg/Fe, 2.2 atomic); Pigeonite, En56Fs35Wo8 (Fe/Mg, 1.6 atomic). †APXS chemistry from Gellert et al. (35). ‡Cr2O3 and
MnO calculated with the amorphous component. §Total Fe as FeO+Fe2O3 because APXS does not distinguish oxidation states. ||FeO required for Fe2+
crystalline phases (olivine,
augite, pigeonite, ilmenite, and magnetite). ¶Fe2O3 required for Fe3+
crystalline phases (hematite and magnetite). #SO3 required for crystalline SO3 crystalline phase (anhydrite).
RESEARCH ARTICLE

martian air (0.02 kg/m3
), and g is the acceleration
due to gravity (3.71 m/s2
). The calculated u*c is
2.6 m/s, which represents the fluid shear veloc-
ity to initiate motion. Because grains in creep
derive a portion of their momentum from colli-
sions by saltating grains, on Earth once saltation
begins, creep can occur down to 0.7 u*c (1.8 m/s
as applied to the Rocknest grains), which repre-
sents the impact threshold for motion. Given a
boundary layer created by winds blowing over
the surface, shear velocities can then be related
to the wind speeds above the surface by the law
of the wall
uz ¼
u*
k
ln
z
z0

where uz is the wind speed at height z above the
surface (taken here as 1 m), k is a constant of
0.407, and z0 is the roughness height where the
idealized logarithmic wind profile is predicted to
be zero. Roughness height varies by grain size
and the height of surface features, such as wind
ripples (7), and also by the height and intensity
of the saltation cloud (43). Rocknest conditions
are unknown, but z0 is taken as 0.3 mm, which
would be the roughness height with wind rip-
ples 10 mm in height. Estimated wind speeds
at 1 m above the surface are ~52 m/s (116 mph)
and 36 m/s (80 mph), without and with saltation,
respectively. As a result of the lower gravity and
reduced atmospheric density on Mars, a greater
hysteresis exists than on Earth between the fluid
and impact thresholds, and saltation impacts upon
grains are more energetic (18, 44, 45). The com-
bined effects suggest that initial transport of the
coarse surface grains probably occurred at lower
wind speeds than those calculated. Conversely,
reactivation of the sand shadow would require
considerably higher wind speeds because of in-
duration of the surface.
Although observations from the Viking Lander
1 suggest that wind speeds of 30 m/s at a height
of 1.6 m occurred during its 2-year lifetime (46),
we do not known how often Mars winds can be
capable of transporting 1- to 2-mm grains. The
wind estimates above suggest that formation
of the Rocknest sand shadow has involved rare
strong winds and that reactivation of the sand
shadow from its currently indurated state would
require even stronger and rarer winds.
Given the possibility of considerable antiquity
of the Rocknest sand shadow and similar coarse-
grained bedforms on Mars, could their activa-
tion correspond to the martian obliquity cycle?
At low obliquities, the atmosphere collapses onto
the polar caps, but at high obliquity, CO2 is re-
leased to the atmosphere (47, 48). Taken as an
end member, atmospheric density may double at
high obliquity and thereby enhance aeolian ac-
tivity (48). As a comparison with the above val-
ues calculated for the present martian atmosphere,
using 0.04 kg/m3
for atmospheric density, the
calculated fluid u*c is 1.9 m/s and the impact u*c
is 1.3 m/s, which correspond to wind speeds at
the 1-m height of ~37 m/s (83 mph) and 26 m/s
(58 mph), respectively. Although considerably
lower than values calculated for present condi-
tions, rare strong wind events are still implied.
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Acknowledgments: Support from the NASA Mars Science
Laboratory Mission is gratefully acknowledged. The chemical
and mineralogical data presented here are derived from the
archived data sets in the NASA Planetary Data System (PDS)
http://pds-geosciences.wustl.edu/missions/msl, specifically
MSL-M-CHEMIN-2-EDR-V1.0 and MSL-M-APXS-2-EDR-V1.0.
M.B.M. was funded by the Danish Council for Independent
Research/Natural Sciences (Det Frie Forskningsråd Natur og
Univers FNU grants 12-127126 and 11-107019).
W.G. acknowledges partial funding by the Deutsche
Forschungsgemeinschaft (DFG grant GO 2288/1-1).
Some of this research was carried out at the Jet Propulsion
Laboratory, California Institute of Technology, under a
contract with NASA.
Supplementary Materials
www.sciencemag.org/content/341/6153/1239505/suppl/DC1
Supplementary Text
Figs. S1 to S4
Tables S1 and S2
References
23 April 2013; accepted 31 July 2013
10.1126/science.1239505
RESEARCH ARTICLE

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et al.L. A. Leshin
Curiosity Rover
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Volatile, Isotope, and Organic
Analysis of Martian Fines
with the Mars Curiosity Rover
L. A. Leshin,1
* P. R. Mahaffy,2
C. R. Webster,3
M. Cabane,4
P. Coll,5
P. G. Conrad,2
P. D. Archer Jr.,6
S. K. Atreya,7
A. E. Brunner,2,8
A. Buch,9
J. L. Eigenbrode,2
G. J. Flesch,3
H. B. Franz,2,10
C. Freissinet,2
D. P. Glavin,2
A. C. McAdam,2
K. E. Miller,11
D. W. Ming,6
R. V. Morris,6
R. Navarro-González,12
P. B. Niles,6
T. Owen,13
R. O. Pepin,14
S. Squyres,15
A. Steele,16
J. C. Stern,2
R. E. Summons,11
D. Y. Sumner,17
B. Sutter,6,18
C. Szopa,4
S. Teinturier,4
M. G. Trainer,2
J. J. Wray,19
J. P. Grotzinger,20
MSL Science Team†
Samples from the Rocknest aeolian deposit were heated to ~835°C under helium flow and evolved
gases analyzed by Curiosity’s Sample Analysis at Mars instrument suite. H2O, SO2, CO2, and
O2 were the major gases released. Water abundance (1.5 to 3 weight percent) and release
temperature suggest that H2O is bound within an amorphous component of the sample.
Decomposition of fine-grained Fe or Mg carbonate is the likely source of much of the evolved CO2.
Evolved O2 is coincident with the release of Cl, suggesting that oxygen is produced from thermal
decomposition of an oxychloride compound. Elevated dD values are consistent with recent
atmospheric exchange. Carbon isotopes indicate multiple carbon sources in the fines. Several simple
organic compounds were detected, but they are not definitively martian in origin.
T
he exchange of materials between a planet’s
interior, surface, and atmosphere drives the
composition of mineral and chemical consti-
tuents that can create habitable environments on
the terrestrial planets. Surface deposits, including
aeolian fines, form an important record of these
material exchanges. Martian surface fines are es-
pecially interesting because previous chemical
studies by the Viking landers, Pathfinder, Spirit,
and Opportunity (1–4) show that the bulk chem-
ical composition of these materials is relatively
constant at widely spaced locations across the
planet. This can result from a combination of
mechanical mixing on global scales and a sim-
ilarity in the chemical composition of bedrock
and sediments on regional to global scales (5).
The finer-grained fractions, in particular, may
provide information about the average compo-
sition of the martian crust (6).
The Sample Analysis at Mars (SAM) instru-
ment suite onboard the Mars Science Laboratory
(MSL) rover Curiosity provides diverse analyt-
ical capabilities for exploring martian materials,
including volatile and isotopic compositions, and
a search for organic compounds, whether of abiotic
or biological origin (7). Traces of organic com-
pounds have been found in martian meteorites
(8–12), but previous landed missions, most nota-
bly Viking, did not find definitive evidence of
martian organic material (13).
Curiosity’s first sampling campaign took place
at Rocknest, an aeolian sand shadow. The rover
ingested fine-grained Rocknest material into its
two analytical instruments: Chemistry and Miner-
alogy (CheMin), for x-ray diffraction, and SAM,
for analysis of volatiles. Both SAM and CheMin
sampled portions from scooped materials that
were sieved to contain grain sizes 150 mm. Min-
eralogical and chemical results summarized in a
companion paper (14) indicate bulk composition
similar to martian fines analyzed by previous mis-
sions. Plagioclase, olivine, augite, pigeonite, and
minor magnetite are the major igneous minerals
(15). Minor anhydrite and hematite are the only
nonigneous minerals detected. Along with these
crystalline phases, the chemical and mineralogical
analyses indicate that almost half of the 150-mm
fraction comprises amorphous material (14). SAM
performs evolved gas analysis (EGA) with the
quadrupole mass spectrometer (QMS) and iso-
tope measurements of evolved gases using both
the QMS and the tunable laser spectrometer (TLS),
the latter being sensitive to isotopes of CO2 and
H2O. Organic analyses can be performed with the
QMS alone or when it is coupled to the gas chro-
matograph (GC). SAM analyzed four separate
portions from the fifth scooped sample at Rocknest
RESEARCH ARTICLE
1
Department of Earth and Environmental Sciences and School
of Science, Rensselaer Polytechnic Institute, Troy, NY 12180,
USA. 2
Planetary Environments Laboratory, NASA Goddard
Space Flight Center, Greenbelt MD 20771, USA. 3
Jet Propul-
sion Laboratory, California Institute of Technology, Pasadena,
CA 91109, USA. 4
LATMOS, UPMC Univ. Paris 06, Université
Versailles St-Quentin, UMR CNRS 8970, 75005 Paris, France.
5
LISA, Univ. Paris-Est Créteil, Univ. Paris Diderot and CNRS,
94000 Créteil, France. 6
Astromaterials Research and Explora-
tion Science Directorate, NASA Johnson Space Center, Houston,
TX 77058, USA. 7
Department of Atmospheric, Oceanic and Space
Sciences, University of Michigan, Ann Arbor, MI 48109–2143,
USA. 8
Department of Astronomy, University of Maryland, Col-
lege Park, MD 20742, USA. 9
Laboratoire Génie des Procédés et
Matériaux, Ecole Centrale Paris, 92295 Chatenay-Malabry, France.
10
Center for Research and Exploration in Space Science and Tech-
nology, University of Maryland Baltimore County, Baltimore, MD
21250, USA 11
Department of Earth, Atmospheric and Planetary
Sciences, Massachusetts Institute of Technology, Cambridge, MA
02139,USA.12
InstitutodeCienciasNucleares,UniversidadNacional
Autónoma de México, Ciudad Universitaria, México D.F. 04510,
Mexico. 13
Institute for Astronomy, University of Hawaii, Honolulu,
HI 96822, USA. 14
School of Physics and Astronomy, University of
Minnesota, Minneapolis, MN 55455, USA. 15
Department of As-
tronomy, Cornell University, Ithaca, NY 14853, USA. 16
Geophys-
ical Laboratory, Carnegie Institution of Washington, Washington,
DC20015,USA.17
DepartmentofGeology,UniversityofCalifornia,
Davis, CA 95616, USA. 18
Jacobs, Houston, TX 77058, USA. 19
School
of Earth and Atmospheric Sciences, Georgia Institute of Tech-
nology, Atlanta, GA 30332, USA. 20
Division of Geological and
Planetary Sciences, California Institute of Technology, Pasadena,
CA 91125, USA.
*Corresponding author. E-mail: leshin@rpi.edu
†MSL Science Team authors and affiliations are listed in the
supplementary materials.
Table 1. Experiment parameters for four analyses of Rocknest fines. All evolved gases were
analyzed by the QMS; temperature (T) range of gases that were then sent to the GC and TLS are shown.
Rocknest run
Sol
(mission day)
Sample T range
of gas sent to
GC (°C)
Sample T range
of gas sent to
TLS (°C)
Rationale
Run 1 93 146–533 547–702*
GC: Low-T organics
TLS: Predicted T for thermal
decomposition of carbonates
Run 2 96 98–425 440–601
GC: Low-T organics below SO2
evolution T
TLS: Target CO2 from suspected
carbonate peak
Run 3 99 533–822 234–425
GC: High-T organics
TLS: Low-T CO2 and H2O evolution
Run 4 117 251–289 350–443
GC: Narrow T cut for organics
below O2 evolution T
TLS: Narrow T cut targeting
suspected carbonate
*Due to the low volume of gas released by Rocknest in this temperature range, isotope data were not obtained for this run.

(see Table 1 and Materials and Methods). The ex-
act mass of each Rocknest portion delivered to SAM
is not measured by Curiosity, but tests on Earth
are consistent with 50 T 8 mg per portion (16).
Results and Discussion
Volatile Release
The volatile compounds observed in EGA typ-
ically reflect a combination of processes including
desorption of trapped volatiles, mineral thermal
decomposition, and chemical reaction during
heating of the samples (17, 18). Pure minerals and
chemicals produce volatile products at predict-
able temperatures; however, in natural mixtures,
these temperatures can be strongly shifted by
physical characteristics of the samples (e.g.,
grain size) and by interactions between min-
eral and chemical components (17).
All four Rocknest analyses yielded H2O, SO2,
CO2, and O2, in descending order of average abun-
dance (Fig. 1 and Table 2). H2O, CO2, and O2
abundances are relatively consistent from run to
run and track each other within experimental un-
certainty, whereas SO2 abundance is variable from
run to run. Repeated observation of H2O, CO2,
and O2 gas abundances with similar values sug-
gests that differences in sample mass cannot ex-
plain the heterogeneity in SO2 abundance, and thus
the variability must be due to variation in the abun-
dance of S-bearing minerals in different portions.
The H2O observed in Rocknest EGA com-
prises a broad peak centered at ~300°C. Abun-
dance estimates are ~1.5 to 3 weight percent
(wt %) H2O in the 150-mm fraction. The peak
temperature and breadth of the H2O release is
most consistent with bound H2O in amorphous
phases. Specifically, adsorbed H2O, H2O bound
to amorphous phases (e.g., amorphous alumino-
silicate materials, nanophase ferric oxides and
oxyhydroxides), interlayer H2O from phyllosili-
cates, dehydration of several salts, and dehydration
of ferric oxyhydroxides could have contributed
to the lower-temperature H2O release (Fig. 2).
Higher-temperature H2O could result from more
tightly bound structural H2O and/or OH in mi-
nor minerals present below the CheMin detec-
tion limit, as well as H2O occluded in minerals and
glasses. However, if the water detected was re-
leased from a single host mineral, CheMin should
have detected that host mineral. The lack of ob-
served hydrous crystalline phases in the 150-mm
fraction (15) implies that H2O/OH is derived from
the amorphous component. H2O concentrations
in the amorphous component are estimated to be
3 to 6 wt % H2O.
Unlike the situation for H2O, calculated abun-
dances of carbonate inferred from CO2 released,
sulfate minerals from SO2, and oxychloride com-
pounds (e.g., chlorate or perchlorate) from O2
would all be at or below the detection limits of
CheMin, affirming the complementarity of SAM
and CheMin on Curiosity. The data do not allow
specific determination of whether host materials
for these evolved gases exist as crystalline phases
at abundances less than the 1 to 2% detectable by
CheMin, or whether these volatiles are also hosted
in amorphous materials in the 150-mm fraction.
However, the release temperatures of the gases sug-
gest fine-grained and/or poorly crystalline ma-
terials as the hosts, as discussed below.
The CO2 released from all four Rocknest
runs comprises two major peaks, at ~400° and
~510°C, and a lower-temperature shoulder, which
can be fit as two discrete releases at ~225° and
~295°C (Fig. 3). The two major CO2 peaks to-
gether comprise 70% of the CO2 released. The
highest-temperature CO2 release is consistent with
the thermal decomposition of siderite (19). If this
peak is due entirely to siderite decomposition, it
would imply ~1 wt % siderite in the Rocknest
150-mm fraction. A second possibility is that
this release evolved from the thermal decompo-
sition of nanophase magnesite, because nano-
phase carbonates decompose at temperatures at
least 100°C lower than 2- to 50-mm-sized particles
(17, 20). Calcite is not a likely candidate because
its decomposition begins at 685°C, a temperature
substantially higher than that of the vast majority
of CO2 released from the Rocknest 150-mm
fraction. A third possibility is that the two major
CO2 peaks correspond to CO2 chemically evolved
from two mineral phases, such as siderite and
magnesite, by reaction with HCl (18), which is
observed in the Rocknest EGA (Fig. 1B), likely
from decomposition of a perchlorate salt (see be-
low). Most likely, all three factors (grain size, min-
eralogy, and reaction with HCl) contribute to the
two major CO2 peaks.
The concurrent evolution of CO2 and O2 from
Rocknest suggests that organic carbon (i.e., C con-
6x10
7
5
4
3
2
1
0
counts/s
800700600500400300200100
Sample Temperature (°C)
1.2x10
5
1.0
0.8
0.6
0.4
0.2
0.0
counts/s
Rocknest 1
Rocknest 2
Rocknest 3
Rocknest 4
Rocknest 4
H2O
O2
CO2 SO2
CH3Cl
(x10)
HCN
H2S
HCl
A
B
Fig. 1. Gases released from heated Rocknest aliquots. Relative abundance of molecular ions
diagnostic of specific gases evolved over the 75° to 835°C pyrolysis temperature ramp. (A) The four
most abundant gases evolved from the four Rocknest portions delivered to SAM. Major molecular ions
that saturated the QMS detector were estimated on the basis of other isotopologs of that species. (B)
Traces for m/z 27, 34, 36, and 52, reflecting four minor gases from the Rocknest run 4. Gas species that
constitute the greatest input to the traces are labeled (27 = HCN, 34 = H2S, 36 = HCl, and 52 = CH3Cl),
as are any scaling factors used. Minor contributions from other species are possible (e.g., the low-
temperature peak of the “H2S” trace reflects a contribution from 16
O18
O).

tained in molecules having C, H, O, N, and/or S)
oxidized within SAM is another potential CO2
source. Such reduced carbon might be indigenous
to Mars, delivered from space in the form of inter-
planetary dust particles and micrometeorites,
or part of the instrument background. Molecular
fragments from a reagent carried to Mars for use in
a SAM wet chemistry experiment, MTBSTFA (N-
methyl-N-tert-butyldimethylsilyl-trifluoroacetamide),
have been identified in both empty-cup blank and
Rocknest runs. A small fraction of CO2 (10% of
the total CO2 observed) from combustion of these
organics is suggested by the amount of the most
abundant MTBSTFA-related products, mono- and
bi-silylated H2O (tert-butyldimethylsilanol and 1,3-
bis(1,1-dimethylethyl)-1,1,3,3-tetramethyldisiloxane,
respectively). These sources are discussed below
in conjunction with d13
C measurements and or-
ganic molecular analyses.
Although the intensity and shape of traces at-
tributable to SO2 vary between the Rocknest sam-
ples, overall, the EGA traces indicate that SO2
evolves from ~450° to 800°C. Two main peaks are
observed, at ~500° to 550°C and ~700° to 750°C
(Fig. 1). Possible sources of the evolved SO2 in-
clude the thermal decomposition of sulfates and/or
sulfites, oxidation of sulfides, and S adsorbed onto
particle surfaces, which can persist to relatively high
temperatures (21). Laboratory EGA under SAM-
like conditions shows that iron sulfates produce
SO2 at temperatures consistent with Rocknest ob-
servations. Mg- and Ca-sulfates, including the an-
hydrite observed in Rocknest 150-mm fraction by
CheMin (15), have SO2 evolution temperatures
too high to explain the observed SO2. The high-
temperature tail of O2 peak at ~460°C is coinci-
dent with the initial rise of SO2. This observation
and SAM EGA detections of small amounts of
H2S, OCS, and CS2 evolved at temperatures close
to the higher-temperature SO2 release (Fig. 1) sup-
port the hypothesis that oxidative reactions of re-
duced sulfur phases during heating also contributed
to the evolved SO2.
The onset of release of O2 correlates with the
release of chlorinated hydrocarbons (Fig. 1), sug-
gesting that an oxychloride compound, such as a
chlorate or perchlorate, is the source of the oxygen
and chlorinated volatiles. Laboratory evaluation of
various perchlorates and chlorates has not identi-
fied an unequivocal match to the SAM Rocknest
data, but Ca-perchlorate provides the most reason-
able match, with Fe- and Mg-bearing perchlorate,
various chlorates, and mixtures with other min-
erals that may affect decomposition temperatures
(22–24) as other possibilities.
The likely detection of an oxychloride com-
pound by SAM is consistent with perchlorate ob-
served in samples analyzed by the Wet Chemistry
Laboratory (WCL) and the Thermal and Evolved
Gas Analyzer (TEGA) instrument on the Phoenix
lander (25), which observed a similar O2 release
during analysis of a soil sample. On the basis of
WCL results, Phoenix soils were calculated to
contain 0.4 to 0.6 wt % ClO4
–
(25). If all of the
oxygen detected by SAM resulted from perchlo-
rate decomposition, the estimated ClO4
–
abun-
dance in the Rocknest 150-mm fraction (Table 2)
would be comparable to the abundances ob-
served by Phoenix. This abundance does not
account for all of the chlorine detected by Cu-
riosity’s Alpha Particle X-ray Spectrometer (APXS)
(14), implying the presence of other chlorine-
bearing species at Rocknest.
Chlorine has been detected in every soil ever
analyzed on Mars—in situ at the equatorial and
mid-latitude sites of the two Viking landers (2)
and from equator to mid-latitude by remote sens-
ing from Mars Odyssey spacecraft (26). The
process of perchlorate formation is believed to
start with the oxidation of chlorine in gas-phase
reactions in the atmosphere (27), various chlorine
oxides produced by energetic electrons from ga-
lactic cosmic-ray interaction with the surface ice
(28), heterogeneous mineral-catalyzed photo-
oxidation of surface chlorides (29), or on airborne
dust. The global presence of chlorine, and the de-
tection of perchlorate in fines at two very differ-
ent locations (Phoenix and Curiosity landing
sites), support the hypothesis that perchlorates
are globally distributed in the regolith of Mars.
Perchlorates can be a sensitive marker of past cli-
mate and a potential terminal electron acceptor
for martian biota. They may also form liquid brines
under current martian conditions and contribute
to the oxidation and transformation of martian
6x10
7
5
4
3
2
1
0
counts/s
800700600500400300200100
Sample Temperature (°C)
Rocknest 1
Rocknest 2
Rocknest 3
Rocknest 4
Ca-perchlorate
Gypsum
Bassanite
Mg-perchlorate
Epsomite
Schwertmannite
Goethite
Mg-perchlorate
Ca-perchlorate
Kieserite
Kaolinite
H-Jarosite
Nontronite
Allophane
Montmorillonite
Saponite
Fig. 2. Water release from Rocknest compared to laboratory measurements of mineral break-
down. Water release versus temperature for Rocknest 150-mm fraction measured by the SAM QMS.
Arrows indicate temperatures of water-release peaks determined by laboratory analysis for select hy-
drous minerals phases under conditions similar to that in SAM (17).
Table 2. Abundance of major species released upon heating of Rocknest as measured with
the SAM QMS. Errors reported for molar abundances are the 2s SD from the mean of calculations
done with different m/z values for the same species. Weight % values were calculated with an
estimated sample mass of 50 T 8 mg (2s), with errors propagated including the uncertainty in
molar abundance (14).
Molar abundances (mmol)
Run 1 Run 2 Run 3 Run 4
CO2 8.3 T 2.0 10.8 T 2.6 10.1 T 2.4 10.4 T 2.5
SO2 2.9 T 0.2 13.7 T 1.9 21.7 T 2.9 10.5 T 1.4
H2O 43.3 T 10.7 66.5 T 16.2 54.5 T 9.9 55.9 T 11.9
O2 3.0 T 0.4 5.1 T 0.6 3.7 T 0.4 3.7 T 0.5
Sample weight %
Run 1 Run 2 Run 3 Run 4
CO2 0.7 T 0.2 1.0 T 0.3 0.9 T 0.3 0.9 T 0.3
SO3 equiv. 0.5 T 0.1 2.2 T 0.5 3.5 T 0.7 1.7 T 0.3
H2O 1.6 T 0.5 2.4 T 0.7 2.0 T 0.5 2.0 T 0.5
ClO4 equiv. 0.3 T 0.1 0.5 T 0.1 0.4 T 0.1 0.4 T 0.1
RESEARCH ARTICLE

organic matter when exposed to ionizing radia-
tion at or near the surface or during analytical pro-
cessing. Thus, a widespread presence of perchlorate
salts, spatially and temporally, would have an im-
portant bearing on understanding habitability, or-
ganic matter preservation potential, and organic
biosignature detection on Mars.
Isotopes
The results of the TLS isotopic analyses at Rocknest
are summarized in Table 3. The strategy for the
different temperature ranges of evolved gas sent
to the TLS was developed with the EGA data
to iteratively design experiments that selectively
focused on various gas releases. For example,
run 3 captured the bulk of the H2O peak, and
run 4 focused on the first of the two large CO2
peaks. The EGA data were also used to con-
strain the isotopic composition of C in CO2
and S in SO2.
Hydrogen in all Rocknest samples is highly
enriched in deuterium compared to terrestrial
materials (Fig. 4), with dD values ranging from
~+3900 to +7000 per mil (‰). Run 3 should be
most representative of the “bulk” of the water in
Rocknest, with a value of ~+7000‰. However,
significant variation in the dD value with temper-
ature is observed, with the lower-temperature cut
having the highest dD value and the highest-
temperature cut having the lowest.
The dD values measured in the Rocknest
150-mm fraction are consistent with the SAM
TLS measurements of water in the martian atmo-
sphere taken before Rocknest, which show a
dD value of +5000 T 1000‰ (30). In addition,
the Rocknest dD values are within the range of
values observed by remote-sensing analysis of the
martian atmosphere (31), where telescopic mea-
surements from Earth have previously suggested
a reservoir enriched in D by a factor of ~5 over
terrestrial values. The D-enriched values in a martian
soil are also consistent with D-enriched H2O ob-
served in both bulk (32) and single grains (33)
in martian meteorites.
The close match between the dD values from
H2O in both atmospheric gas and Rocknest sug-
gests that the H2O-rich phases in the amorphous
material were formed either in direct contact
with the atmosphere or through interaction with
volatiles derived from it. The variation of dD
value with temperature may either record long-
term variation of D/H through time or repre-
sent seasonal variations reflecting changes in
the water cycle. It is likely that the water evolved
at the lowest temperatures represents water in
active exchange with the present atmosphere,
whereas the higher-temperature releases could
represent water from a more ancient time. Tele-
scopic measurements suggest that there could
be large variations in atmospheric dD value with
water content of the atmosphere and season
(31), and such variations may be reflected in the
Rocknest results.
Like hydrogen in H2O, 13
C-enriched CO2 has
also been observed in the atmosphere at Gale
crater with SAM TLS (30) and QMS (34), with
an average d13
C value measured to date of ~+46‰.
Unlike hydrogen, however, the CO2-bearing phases
in Rocknest soil do not fully reflect this 13
C-
enriched atmospheric value. Rather, d13
C values
of CO2 evolved from Rocknest and analyzed
by TLS range from –6 to +20‰ (Table 3), and
estimates of d13
C over the two major CO2 peaks
using QMS data average ~+18 T 10‰, consistent
with the TLS results. These values overlap with
d13
C values from both carbonates and refractory/
reduced carbon in martian meteorites (Fig. 5).
Consistent with the above discussion of sev-
eral possible CO2 sources in SAM analyses of
Rocknest, the d13
C compositions likely reflect
mixing of multiple carbon sources. The concurrent
evolution of CO2 and O2 from Rocknest suggests
that partial combustion of reduced carbon could
contribute to evolved CO2. d13
C associated with
the CO2 release between 250° and 450°C might
reflect some contribution from this combusted
carbon. Previous studies of martian meteorites
have shown that reduced carbon is present either
as an indigenous component or from exogenous
meteoritic input (8, 10–12).
The Rocknest d13
C values suggest a hint of
13
C enrichment, consistent with d13
C values ob-
served in martian meteorite carbonates. Specif-
ically, the data from run 4, which most closely
capture the largest CO2 peak, has a d13
C value
of +20 T 10‰, which is similar to carbonate
measured in the Nakhla meteorite (35). This value
is lower than would be expected for carbonate
formed from the modern atmosphere as measured
by SAM TLS (30). It is possible that this CO2 re-
lease is a mixture of carbonate-derived CO2 with
a high d13
C value and CO2 depleted in 13
C and
thus does not reflect the true carbon isotopic
composition of the carbonate. It is also possible
that the carbonate does have low d13
C values as
observed in some of the martian meteorites, sug-
gesting that the atmosphere has changed through
time (36). Overall, the data support a minor amount
of carbonate in martian soil derived from atmo-
sphere interaction with only transient water (37).
The sulfur isotopic composition of SO2 re-
leased during run 4 was determined from QMS
data at a mass-to-charge ratio (m/z) of 64, 65, and
66. The Rocknest 150-mm fraction, including
analyses of both of the major SO2 evolution peaks,
1.6x105
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
counts/s
800700600500400300200100
Temperature (ºC)
-3x104
-2
-1
0
1
Residual
Peak 1
Peak 2
Peak 3
Peak 4
mass45
fit-mass45
Res-mass45
Fig. 3. Deconvolution of CO2 release from Rocknest. Rocknest run 2 CO2 (mass 45) versus temper-
ature (red). Gray peaks are Gaussian fits to overall CO2 release that sum to mass 45 fit (blue line). CO2
fractions in each of the four peaks are 0.07, 0.22, 0.41, and 0.30, respectively.
Table 3. Isotopic composition of volatiles released upon heating of Rocknest as measured with
the SAM TLS. Blank cup corrections have been applied as described in materials and methods.
Rocknest run T range sampled (°C) d13
C in CO2 (‰) dD in H2O (‰)
Run 3 234–425 –6 T 14 7010 T 66
Run 4 350–443 20 T 10 4250 T 60
Run 2 440–601 3 T 9 3870 T 60

have d34
SVCDT of 0 T 10‰, consistent with sulfur
isotopic compositions measured in martian me-
teorites (38, 39).
Organic Matter
Chlorohydrocarbons comprising chloromethane
(CH3Cl), dichloromethane (CH2Cl2), trichlorometh-
ane (CHCl3), and chloromethylpropene (C4H7Cl)
were detected during SAM GC-MS analyses (Fig. 6
and Table 4). Chloromethanes detected by SAM
in runs 1, 2, and 4 were at ~nanomole levels and
above SAM background. Run 3 produced lower
abundances of chloromethanes (typically observed
at 300°C) because only a high-temperature cut
of evolved gases were transferred to the GC. Mi-
nor amounts of HCN, CH3Cl, CH2Cl2, and CHCl3
are also observed in SAM EGA data (Fig. 1B). The
abundance of these species is more than two or-
ders of magnitude lower than that of the most
abundant volatile released—H2O.
The abundances measured by SAM are higher
than the picomole levels (up to 40 parts per bil-
lion) for chloromethane and dichloromethane
previously measured by the Viking pyrolysis gas
chromatography–mass spectrometry (GC-MS) in-
struments after heating the samples of scooped
fines up to 500°C (13). Biemann et al. (13) at-
tribute the Viking results to chlorohydrocarbons
derived from cleaning solvents used on the instru-
ment hardware, not from the martian samples them-
selves. Recently, Navarro-González et al. (40)
suggested that these chlorohydrocarbons may
have formed by oxidation of indigenous organic
matter during pyrolysis of the soil in the pres-
ence of perchlorates, but Biemann and Bada (41)
disagree with this conclusion.
The absence of detectable chlorohydrocarbons
in the SAM blank run indicates that the chlorohy-
drocarbons measured at Rocknest are not directly
attributable to the SAM instrument background
signal. However, the associated release of chloro-
methanes, O2, and HCl strongly suggests that
these chlorohydrocarbons are being produced
within SAM by chlorination reactions involv-
ing an oxychloride compound in the Rocknest
150-mm fraction and an organic carbon pre-
cursor (23). Three sources for the organic carbon
of this reaction are possible: (i) terrestrial sources
within the SAM instrument or the Curiosity sam-
ple chain; (ii) exogenous carbon in the martian
surface materials derived from infalling meteor-
itic carbon; and (iii) martian indigenous organic
matter. A feasible explanation involves terrestrial
carbon derived from the MTBSTFA, whose reac-
tion products were identified in both the blank
and soil EGA and GC analyses. On the basis of
laboratory pyrolysis GC-MS experiments, pyro-
lytic reaction of martian Cl with organic carbon
from MTBSTFA in SAM can explain the pres-
ence of the chloromethanes and chloromethyl-
propene detected by SAM. However, we cannot
rule out the possibility that traces of organic carbon
of either martian or exogenous origin contributed
to some of the chlorohydrocarbons measured by
SAM at Rocknest.
Overall, SAM analyses indicate that martian
fines contain a number of materials with bound
volatiles that can be released upon heating. These
volatile-bearing materials are likely very fine-
grained and associated with the amorphous com-
ponent of martian regolith. The fines could be a
good source of water, CO2, and other volatiles to
be leveraged by future human explorers on Mars.
Isotopic compositions support an atmospheric
source of the water and possibly CO2, consistent
with previously proposed formation mechanisms
for carbonate and perchlorate in the fines that in-
volve interaction with the atmosphere. Although
martian organic matter was not definitively detected,
the presence of materials that produce substantial
amounts of oxygen upon heating suggests that
detection of such compounds in martian soils will
be difficult with pyrolysis techniques. The fines on
Mars reveal a complex history, reflecting global,
regional, and local-scale processes.
Fig. 4. Tunable laser spec-
trometer data showing hy-
drogen isotope enhancement
in Rocknest. Section of a sin-
gle spectrum (60 s integration)
downloaded from Curiosity
(black) for the Rocknest 3 sam-
ple run, showing large HDO
line depth compared to calcu-
lated HITRAN spectrum (red)
based on terrestrial SMOW wa-
ter isotope ratios. The HDO
line is ~4 times the depth of
that predicted for SMOW, so
that the D/H ratio is ~8 times
that of SMOW, corresponding
to a dD value of ~7000‰, as
reported.
Fig. 5. Carbon isotopes in relevant solar system reservoirs. Carbon isotopic composition of ma-
terials from Mars (44–46), Earth (47), and carbonaceous chondrite meteorites (48) for comparison the
values measured in Rocknest and the martian atmosphere (30) by the Mars Curiosity Rover.
RESEARCH ARTICLE

Analysis of Surface Materials by Curiosity Mars Rover - Special Collection

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