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et al.
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Sci. Adv.
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, eadr0010 (2025) 15 January 2025
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SPACE SCIENCES
Wave ripples formed in ancient, ice-
free lakes in Gale
crater, Mars
Claire A. Mondro
1
*, Christopher M. Fedo
2
, John P. Grotzinger
1
, Michael P. Lamb
1
, Sanjeev Gupta
3
,
William E. Dietrich
4
, Steven Banham
3
, Catherine M. Weitz
5
, Patrick Gasda
6
, Lauren A. Edgar
7
,
David Rubin
8
, Alexander B. Bryk
4
, Edwin S. Kite
9
, Gwénaël Caravaca
10
,
Juergen Schieber
11
, Ashwin R. Vasavada
12
Symmetrical wave ripples identified with NASA’s Curiosity rover in ancient lake deposits at Gale crater provide a
key paleoclimate constraint for early Mars: At the time of ripple formation, climate conditions must have sup
-
ported ice-
free liquid water on the surface of Mars. These features are the most definitive examples of wave rip
-
ples on another planet. The ripples occur in two stratigraphic intervals within the orbitally defined Layered Sulfate
Unit: a thin but laterally extensive unit at the base of the Amapari member of the Mirador formation, and a sand-
stone lens within the Contigo member of the Mirador formation. In both locations, the ripples have an average
wavelength of
~
4.5 centimeters. Internal laminae and ripple morphology show an architecture common in wave-
influenced environments where wind-
generated surface gravity waves mobilize bottom sediment in oscillatory
flows. Their presence suggests formation in a shallow-
water (
<
2 meters) setting that was open to the atmosphere,
which requires atmospheric conditions that allow stable surface water.
INTRODUCTION
Debate about the paleoclimate conditions on early Mars ranges from
cold and wet scenarios, with abundant glaciogenic processes and
limited standing water free of an ice cover [e.g., (
1
,
2
)], to warm and
wet scenarios, with abundant standing water free of ice [e.g., (
3
)].
While there is geomorphic evidence for surface water activity across
Mars (
3
–
8
), the climate models lack consensus on the precise condi-
tions, timing, and duration of surface water, specifically whether
standing water would be stable in early Mars atmospheric conditions
(
1
,
2
,
9
,
10
). Detailed documentation of sedimentary structures pre-
served in ancient martian strata is an essential element for resolving
this debate because they are capable of recording processes that pre-
serve precise paleoenvironmental conditions, which are critical for
constraining and validating climate models. Specifically, features
such as wave ripples that are formed by the interaction of atmo-
sphere, water, and sediment can be used to constrain both aqueous
and atmospheric conditions (
11
).
Both Earth and Mars have (and had) a well-
defined atmosphere,
hydrosphere, cryosphere, and lithosphere. Processes within these
systems generate currents of air, liquid water, and ice, which trans-
port sediments from sites of weathering and erosion where they are
formed to sites of deposition where they accumulate to create a re-
cord of sedimentary rocks (
12
). As on Earth, past surface processes
on Mars, including within Gale crater—the site of exploration by
NASA’s Mars Science Laboratory rover Curiosity—are recorded as
suites of sedimentary structures and lithologic textural parameters,
which can be measured by orbiter and rover cameras and analytical
instruments (
13
–
18
).
Here, we document the occurrence of symmetrical, shallow-
water,
wave-
generated ripples at two different locations within the predom-
inantly aeolian Mirador formation (
19
) within Gale crater, Mars. The
sedimentary features documented here are the most definitive ex-
amples of wave oscillation ripples documented on another planet.
Possible wave ripples have only documented once before in Gale
crater (
11
), but in that case, other formation mechanisms could not
be confidently ruled out. Wave ripples have so far have not been
detected anywhere else on Mars. Symmetric wave ripples have spe-
cific environmental implications, as their formation requires sedi-
ment transport and deposition by oscillatory currents acting on a
shallow lake bottom as a result of wind-
generated gravity waves on
the lake surface. In the case of Mars, wave-
ripple formation requires
a climate with sufficiently higher atmospheric pressure, warmth,
and humidity than at present to sustain surficial bodies of liquid
water absent of an ice cover. To reconcile the geomorphic evidence
for lakes with early Mars climate models, previous studies have sug-
gested that water bodies on Mars would have been ice covered (
20
–
22
).
Observations of wave ripples disprove this long-
standing hypothesis
and provide a key geologic constraint on the depositional environ-
ment and associated climate models.
Geologic and stratigraphic context
Since arriving at the Bradbury landing site in Gale crater in 2012,
the Curiosity rover has ascended the northern slopes of Aeolis Mons
(informally known as Mount Sharp), climbing more than 800 m of
elevation along a traverse more than 32 km in length. The rocks that
now comprise the
~
5-
km high sedimentary mound within Gale cra-
ter were deposited during Hesperian time,
~
3.0 to 3.7 billion years
ago (
23
). The stratigraphic succession has been divided into group-
level packages (Mount Sharp and Siccar Point), which, in turn, are
1
division of Geological and Planetary Sciences,
california
institute of
technology,
Pasadena,
cA 91125, USA.
2
department of
earth and Planetary Sciences, University
of
tennessee, Knoxville,
tn 37996, USA.
3
department of earth Science and engi-
neering, i
mperial c
ollege l
ondon, l
ondon, UK.
4
earth and Planetary Science, Uni-
versity of c
alifornia, Berkeley, Berkeley, c
A 94709, USA.
5
Planetary Science i
nstitute,
tucson, AZ 85719, USA.
6
los Alamos national laboratory, l
os Alamos, nM 87545,
USA.
7
U.S. Geological Survey Astrogeology Science c
enter, Flagstaff, AZ 86001,
USA.
8
department of earth and Planetary Sciences, University of c
alifornia, Santa
cruz, Santa c
ruz, c
A 95064, USA.
9
department of the Geophysical Sciences, Univer
-
sity of chicago, chicago, il 60637, USA.
10
institut de Recherche en Astrophysique et
Planétologie, Université de
toulouse cnRS, cneS,
toulouse, France.
11
department
of
earth and Atmospheric Sciences,
indiana University, Bloomington,
in 47405,
USA.
12
Jet Propulsion laboratory, c
alifornia i
nstitute of
technology, Pasadena, c
A
91109, USA.
*c
orresponding author. email: cmondro@
caltech.
edu
copyright © 2025
the
Authors, some rights
reserved; exclusive
licensee American
Association for the
Advancement of
Science. no claim to
original U.S.
Government Works.
distributed under a
creative c
ommons
Attribution
nonc
ommercial
license 4.0 (
cc BY- nc
).
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subdivided into mappable formation-
and local member-
level sub-
units (Fig. 1). On the basis of the observation that Mount Sharp
strata are horizontal or close to horizontal in attitude (
14
,
24
–
26
), we
use elevation as a proxy for stratigraphic thickness.
Along Curiosity’s traverse up-
section through the Mount Sharp
group, the stratigraphy records an overall transition from more aque-
ous to more aeolian depositional environments. The Murray forma-
tion is dominantly composed of laminated mudstone representative
of having been deposited in lacustrine and lacustrine-
margin pa-
leoenvironments (
14
,
17
,
24
,
25
,
27
–
29
). Several members within the
Murray formation consist of finely laminated mudstones with few
obvious stratigraphic discontinuities, which have been interpreted to
represent long episodes of lake deposition with standing water
(
14
,
15
,
17
). The Carolyn Shoemaker formation (Fig. 1D) records an
overall shallowing-
up sequence of interbedded lacustrine mudstones
and marginal and fluvial sandstones (
19
,
30
,
31
).
The overlying Mirador formation marks a transition into pre-
dominantly aeolian depositional environments (Fig. 1D). Collec-
tively, the Dunnideer, Port Logan, and Contigo members encompass
160 m of aeolian sand containing decimeter-
to multimeter-
scale
trough cross-
stratification (
19
). The Prow outcrop is one of the mul-
tiple lenticular deposits interstratified within the Contigo aeolian
sandstones [(
32
); fig. S1]. The Catrimani member is composed of
thin, planar, aeolian laminae (
19
), directly overlain by the Amapari
Marker Band (AMB). The AMB is identifiable in orbital data as a
dark, erosionally resistant bench (Fig. 1C) that can be traced nearly
continuously along the northwest side of Mount Sharp (
33
,
34
).
RESULTS
AMB outcrop
Curiosity first approached the AMB at the Amapari location (Fig.
1C) along the west side of Marker Band Valley (MBV). Alternating
centimeter-
scale resistant and recessive beds make up the lower unit
of the AMB, containing structures interpreted as symmetric ripples
(Fig. 2). The AMB, including the ripple unit, outcrops continuously
around MBV. At the Amapari location, the ripple unit is 15 cm thick
and contains five resistant rippled beds. The top of the uppermost
ripple bed is a sharp contact with an overlying thickly laminated
unit (Fig. 2C) that transitions into the thin, planar, aeolian laminae
of the Chenapau member.
The ripples within the AMB resistant beds are composed of paral-
lel millimeter-
scale laminae that can be traced continuously through
the ripple troughs and crests (Fig. 2A and fig. S2). Individual resis-
tant beds are 1 to 2 cm thick. Internal laminae within the recessive
beds (where visible) appear to uniformly drape the rounded ripple
crests and define upward building of the ripples (fig. S3). The ripple
crests in successive resistant beds are aligned near-
vertically with no
observed truncation of crests or laminae (Fig. 2A), indicating ripples
formed by vertical accretion with little translation during higher
sediment fallout. The rapid sedimentation during ripple formation
and the darker tone of the AMB outcrop relative to the underlying
stratigraphy suggest that the ripple layers are not formed from lo-
cally reworked lakebed sediments. The sediment was most likely
sourced from further away, either as wind-
blown sediment or in sur
-
face runoff from a location beyond the Amapari outcrop location.
At the Amapari location within the AMB, the ripples have an aver
-
age wavelength (
λ
) of 4.5 cm, with a range of 3.83 to 5.32 cm (table S1).
The symmetry index ranges from 0.73 to 1.20 (mean
=
0.96), indicat-
ing that the ripples are symmetrical, consistent with ripples formed
from oscillatory currents under surface gravity waves known as wave
ripples. The average ripple height (
h
) is 0.66 cm and the average aspect
ratio (
h
/
λ
) of the ripples is 0.13, which is consistent with orbital wave
ripples (
35
). The grain size of the ripple beds is fine sand or smaller, as
it is not detectable in Mars Hand Lens Imager (MAHLI) images
(
36
). Linear ripple crests with occasional tuning-
fork bifurcation, also
−4100
−4000
Mount Sharp
Jura
Knockfarril
Hill
Glasgow
Stimson
Siccar Point
Lithology
Member
Formation
Group
Mercou
Pontours
Dunnideer
Port Logan
Contigo
−3900
Catrimani
Amapari
−3800
Mirador
Chenapau
Carolyn
Shoemaker
Elevation
(m)
N
500 m
20 m
N
A
Mirador butte
The Prow
B
C
N
Marker Band V
alley
Amapari
location
200 m
B
D
C
Mudstone with
faint
laminations
Thinly bedded
lenses
Ripple
cross-
lamination
Sandstone (Mt
Sharp group)
Sandstone
(Siccar Point
group)
Planar and
low-angle
cross-strata
Cross-stratified
sandstone
Mudstone
Lithology key
Fig. 1.
Location of the Amapari Marker Band and Prow outcrops.
Along the c
uriosity traverse [(
A
), gray line] through the Mirador formation, the rover observed sym-
metric ripple marks within the Prow outcrop near the base of Mirador butte at elevation
−
3950 m (
B
) and the Amapari Marker Band (AMB) outcrop along the west side of
Marker Band
valley (MB
v) at elevation
−
3860 m (
C
). Red stars indicate the locations of the ripple-
containing outcrops within the stratigraphic column (
D
) along the MSl
traverse (A).
the Prow is one of the multiple lenticular outcrops within the c
ontigo member.
the AMB outcrops are nearly continuously around MB
v [(
c): solid orange line],
often forming flat, erosionally resistant benches (inner edge traced in dashed orange line).
the basemap used in (A) to (
c) is a Mars Reconnaissance Orbiter h
iRiSe mosaic
generated by c
alef
et al.
(
61
,
62
) and accessed through the nASA Planetary data System.
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, eadr0010 (2025) 15 January 2025
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consistent with oscillation ripples (
37
), are seen in planview along the
top of the AMB bench at the Amapari location (Fig. 2B), oriented con-
sistently southeast-
northwest (table S1 and texts S1 and S2).
Prow outcrop
The Prow outcrop is an
~
18-
m-
long and up to 0.7-
m-
thick lenticular
outcrop (Fig. 3A) located near the base of Mirador butte in the Con-
tigo member [(
32
); Fig. 1B and fig. S1]. At the base of the Prow is a
~
40-
cm-
thick section of decimeter-
scale cross-
bedding indicating
unidirectional flow to the east (Fig. 3C). This unit is overlain by a
~
30-
cm interval of flaser bedding where sand ripples and wavy beds
are interbedded with fine-
grained sediment drapes (Fig. 3, B and E).
Near the top of the flaser bedded interval, symmetric ripples appear
in single layers and amalgamated ripple stacks (Fig. 3, C and D). The
amount of sedimentation and the stratigraphic pattern through the
outcrop suggest that the Prow was not formed of predominantly re-
worked sediment from the stratigraphy directly underlying the out-
crop. The distance to the sediment source is unclear from the data
examined here and the sediment could have been transported via
either wind or water from beyond the water body.
Ripple crests and troughs are both variably preserved throughout
the rippled layer in a complex and interwoven cross-
stratification
pattern (
37
). The ripples are composed of fine to medium sand (me-
dian grain diameter,
D
50
=
389
μ
m) and the draping sediment is
very fine sand or finer (Fig. 3E), below the limit of resolution of
MAHLI images (
36
).
Within the Prow the symmetric ripples have an average wave-
length of 4.6 cm, with a range of 3.48 to 5.86 cm (table S2 and text
S2). The symmetry index ranges from 0.78 to 1.16 (mean
=
1.00),
indicating that the ripples are symmetrical, consistent with ripples.
The average ripple height is 0.35 cm and the average aspect ratio
(
h
/
λ
) of the ripples is 0.074. Ripple crests are oriented approximately
NNE/SSW (table S2), perpendicular to the outcrop face (Fig. 3B).
Wave-
generated origin
Distinguishing between current and wave-
influenced ripples de-
pends on the wavelength and symmetry of the ripples. On Earth,
current ripples in sand (i.e., from unidirectional flow) generally form
at wavelengths of 8 cm and larger and are expected to be slightly
larger under reduced gravity on Mars (
38
). Wave ripples, in contrast,
can form at smaller wavelengths. The ripples in both the AMB and
the Prow have wavelengths
<
6 cm (mean
=
4.5 and 4.6 cm, respec-
tively), which is smaller than current ripples are expected to form.
Wave ripples have a symmetry index of
<
1.5, while current ripples
have a symmetry index of 3.0 or greater (
39
). The symmetry indices
of both the AMB and Prow ripples are consistent with symmetric
wave ripples. On the basis of the wavelength and symmetry measure-
ments, our conclusion is that both sets of ripples are wave influenced.
A
3 cm
sol03674 mcam03228
sol03642 mcam03019
sol03644 MAHLI Mixiguana target
15 cm
N
h
= 0.72 cm
Crest
Current
Ripple unit
Thickly laminated unit
B
C
20 cm
Fig. 2.
Symmetric ripple marks in the AMB outcrop.
Symmetric ripple marks (
A
) are observed within the AMB outcrop. Ripple crests are identified with yellow arrows
(A) and are aligned near-
vertical (white arrow) in successive ripple layers. i
nternal laminae can be traced continuously through the ripple troughs. i
n plan view (
B
), the
ripple crests are linear with occasional tuning-
fork bifurcation, oriented consistently nW/Se
. the AMB ripple unit is laterally extensive, of consistent thickness, and is con-
formably overlain by a unit of planar laminae [(
C
): contact is covered here—dotted line is inferred contact].
the AMB ripple unit at the Amapari location is
~
15 cm thick
and is composed of five resistant beds containing symmetric ripple marks. i
mage credit: nASA/JPl
- caltech/MSSS.
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