CRISM observations of putative paleolakes in Cankuzo and Luqa craters exhibit spectral features consistent with the activity of water. The spatial distributions suggest different formation scenarios for each site. In Cankuzo the distribution suggests postimpact alteration whereas in Luqa there are hints of possible formation of a layer of phyllosilicate materials

Blanco, Armando

Fonti, Sergio

Marzo, Giuseppe A.

Orofino, Vincenzo

Roush, Ted L.

NASA Technical Reports Server

EPSC Abstracts
Vol. 5, EPSC20l0-PREVIEW, 2010
European Planetary Science Congress 2010
@ Author(s) 2010
Spectral Evidence of Aqueous Activity in Two Putative
Martian Paleolakes
Ted L. Roushl, Giuseppe A. Marzo2'l, Sergio Fonti3, Vincenzo Orofino3, and Armando Blanco3
1NASA Ames Research Center, Moffett Field, CA 94035-0001, USA, 'Bay Area Environmental Research Institute,
Califomia, USA, 3Universit6 del Salento, Lecce, Italy
Abstract
CRISM observations of putative paleolakes in
Cankuzo and Luqa craters exhibit spectral features
consistent with the activity of water. The spatial
distributions suggest different formation scenarios for
each site. In Cankuzo the disribution suggests post-
impact alteration whereas in Luqa there are hints of
possible formation of a layer of phyllosilicate
materials.
l.Introduction
Putative paleolakes in Martian impact craters have
been discussed as valuable targets for exploration [1].
They have been suggested as landing sites for in situ
and sample-return missions since they should provide
information about the dynamics of the sedimentary
processes, the climate under which they were formed,
and represent environments providing conditions
favorable to preserving evidence of biomarkers.
Here we investigate CRISM observations ofputative
paleolakes on Mars to evaluate the evidence for the
presence of mineral spectral signatures indicative of
the past presence of water at these sites.
1.1 Site Selection and Background
Cankuzo (19.39 S. Lat., 52.05 E. Long.) and Luqa
(18.23 S. Lat., 131.81 E. Long.) craters were selected
based upon morphologic features suggestive of the
ancient presence of standing bodies of water [2].
These craters do not appear to have undergone major
modification by subsequent impacts. Cankuzo and
Luqa are not included in the studies of [3-6], and are
in regions where sheet silicates are repor0ed [7]. It is
unclear if Cankuzo and Luqa were investigated by [8]
and they were not studied by [9].
l.2Data Analysis
CRISM is a spectrometer that from orbit provides
-18-200 m/pixel spatial sampling [0], CRISM data
have been interpreted to indicate the presence of
several phyllosilicates at many locations and the
range of associated chemistry include Al- to Fe-Mg-
rich materials [11,12]. The available CRISM data for
Luqa and Cankuzo craters are shown in Figures la
and e. The CRISM data were converted to apparent
UF, divided by the cosine of the incidence angle
[10,12] and the atmospheric contribution addressed
using the volcano-scan conection of [13]. A de-
spiking and de-striping algorithm [14] was applied
and geo-referencing allows comparison with other
maps of the area. We focused on the spectral
parameters of tlsl associated with
hydrated./trydroxylated silicates, sulfates, and
carbonates. Each parameter map is visually
evaluated for spatial coherence and when identified,
confirmation involves extraction of individual spectra.
3. Results
Figure I shows the observations for Cankuzo
(MSP_40A8, MSP_81C2, MSP_74C8, and
FRT_112C9) and Luqa (MSP_3238, MSP_64DF,
FRT_11D18 and FRT_1192C) craters, illustrating
high values of the OLINDEXJ [OL2, 16] and
D2300.
Average spectra of Luqa and Cankuzo where a strong
OL2 value (Ol and 02) was detected are shown in
Figarc 2a. These can be compared to laboratory
reflectance spectra of olivines @g. 2b), low calcium
pyroxene (LCP, Fig. 2b) and high calcium pyroxenes
(HCP, Fig. 2b). The local minima near 1 pm and
between 2.0 and 2.5 pm in the Cankuzo and Luqa
spectra are consistent with a HCP, The different
minimum position in the 2-2.5 pm region suggests
the HCP compositions in Cankuzo and Luqa are
different. The width of the rninimum near 1 pm in
the spectra suggests a significant contribution from
olivine, although in Luqa the olivine is either less
https://ntrs.nasa.gov/search.jsp?R=20100038462 2019-08-30T13:07:58+00:00Z
Figure 1: Inset shows locations ofCankuzo and Luqa.
a) Thin/thick solid lines are CRISM MSP/FRT
observations ofLuqa. Red is OL2 and green D2300.
Dashed line is HiRISE observation
ESP-0135527-1615. b) Overlay ofCRISM and
I{iRISE, dashed/solid line areas arc in panel c and d,
respectively. Spectral data werE extractsd at points
Pl, P2, and 01. c) CRISM observations ofluqa on
MOLA topography, the regions from panel b and d
are shown. d) dune field in panel b enlarged' values
of OL2 are high in areas surrounding the dune field,
e) Same as panel a, but for Cankuzo. 0 CRISM
observations at Cankuzo crater on HiRISE
ESP-012541-1600. The doned line indicat€s a series
of out+rops, the solid line is an area in panel h.
CRISM spectra were extract€d ftom points 02 and
P3. g) CRISM observations ofCanluzo on MOLA
topography. Dotted line outcrops on the crater wall
(panel D and the outline the position ofthe region
shown in panel h. h) Small crater outside the
Cankuzo.
Average spectra of two locations in Luqa ('Pl and P2)
and one spectrum ofCankuzo (P3) where strong
values ofD2300 were detected are shown in Figure
2c. These spectra are compared to laboratory spectra
of phyllosilicates @g. 2d and the associated inset)'
The two Luqa spertra exhibit minima, near 1'92 and
232 W Fie.2c, vertical dotted line) and the
Cankuzo spectrum exhibits two minima near 1.92
and 2.305 Fm (FlC. 2c, vertical solid line). The
former can be attributed to molecular waler and the
latter to hydroxyl in mineral structures [17]' The
minima positions from Luqa and Cankuzo are
consistent with the laboratory saponite and
pyrophyllirc-talc spectra, respectively, although in
both cases a mixture ofthe minerals shown in Fig. 2d
can not be precluded. We interpret the CRISM
spectra as suggesting the presence ofsecondary
minerals (Mg-bearing phyllosilicates) in both craters
mixed with a primary fenous-bearing component
rigrrc z.ffit u for Luqa (thin lines, left axis)
and Cankuzo (ttrick lines, right axis). b) Laborarory
spectra ofolivines (dashed and dash-dot black lines)'
LCP (solid black line), and HCP (dashed and dash-
dot gray lines). c) Spectra for Luqa (thin lines, left
axis) and Cankuzo (thick line, right axis) craters.
The solid and dotted vertical lines indicate the
minimum in the 2.2-2,35 pm regton' d) Laboratory
spectra of Fe-Mg-bearing phyllosilicates. The inset
enlarges the 2.26-2.38 lun region with major/minor
tick every 0,M/0.01 pm. The solid and doued
vertical lincs correspond to the positions ofthe same
lines shown in Panel c.
4. Discussion
There is a sipificant spatial extent of the primary
mineral signatures in both craters with restricted
spatial ext€nt where both primary and sccondary
minerals occur. The spatial distribution of the
secondary minerals is significantly different in the
two craters.
At Luqa, the secondary minerals occu in the central
uplift with limited distribution tlnoughout thc crater
floor region (Figs, la-lc). This is reminiscent of a
pattem interpret€d to suggest post-impact
hydrothermal activity in Toro crater [18].
There is an occurrence of the unit indicated by the
OL2 that lies outside Cankuzo and appears associatpd
with the small crater near the southeast rim (Figs. lf-
lh) and this is where the D2300 patameter is sFong
(Fig 1f-1h). MSP observations to the north and south
do not reveal any additional major occurrences of
D2300 suggesting aeolian activity is not the source of
(HCP and/or otvine).
the material. There is a lineament delineated by the
OL2 in the southeast crater wall (Figs. lf and 1g) and
continues to the southwest where a concentration of
the D2300 unit occurs (Fig. lf-lg) raising the
possibility the D2300 unit indicates a layered deposit.
The spatially coherent D2300 pattem near the small
crater suggests an underlying layer exposed by the
impact process and the depth of this small crater
extends to about the same level as the lineament
defined by OL2 and D2300 identified in the wall of
Cankuzo. Thus one speculation is that during the
impact process the small crater excavated the same
material from depth that is exposed in the wall of
Cankuzo.
The lineament in the wall of Cankuzo suggests two
possible genetic scenarios. Both involve the presence
of a layer prior to the impact of Cankuzo crater. In
the first scenario alteration and/or deposition of the
phyllosilicate layer predates the formation of
Cankuzo and the unit has been exposed by the
cratering process. In the second scenario a pre-
existing permeable, or semi-permeable, layer
predates the impact and the phyllosilicates were
formed by post-impact hydrothermal alteration
occurring along this pre-existing layer. Although the
pyrophyllite-talc mineralogy associated with the
spectra of Cankuzo suggest an elevated temperature
during formation ofthe phyllosilicate phase, this fact
alone does not favor selection of either scenario.
This is due to relatively close proximity of Cankuzo
to the rims of the older Huygens crater (-170 km)
and Hellas basin (-750 km). Impacts associated with
both of these larger craters could easily emplace
ejecta deposits of pre-existing materials, or induce
significant hydrothermal systems due to the energy
associated with the large impact events.
Acknowledgements
Support from the NASA Mars Data Analysis
Program is gratefully acknowledged.
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Spectral Evidence of Aqueous Activity in Two Putative Martian Paleolakes

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