8/3/2019 Deposits of Phyllosilicaates in Terby Crater Hellas Region Mars - V Ansan Et Al 2007

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European Space Agency

European Mars Science and Exploration Conference: Mars Express & ExoMars

ESTEC, Noordwijk, The Netherlands, 12 - 16 November, 2007

DEPOSITS OF PHYLLOSILICATES IN TERBY CRATER (HELLAS REGION, MARS) FROM

MULTI-DATASETS (OMEGA/MEX, THEMIS, MOC and HIRISE). V. Ansan1, D. Loizeau

1, N.

Mangold1, Ph. Masson, A. Gendrin

2, S. LeMouelic

3, F. Poulet

2, B. Gondet

2, Y. Langevin

2, J-P. Bibring

2, G.

Neukum4

and the OMEGA co-investigator TEAM,1Lab. IDES-UMR8418, bt. 509, Universit Paris-Sud,

91405 Orsay cdex, France,2Lab. IAS-UMR8617, bt. 121, Universit Paris-Sud, 91405 Orsay cdex, France,

3Lab. Plantologie et godynamique, 3 rue de la Houssinire, BP 9220, 44322 Nantes cdex 3, France. 4FU,Berlin, Allemagne. veronique.ansan@u-psud.fr

Section 1: Terby impact crater is located at the

northeastern part of Hellas region (75E 30S) on

the cratered highlands. Using multi-dataset available

on this area, we investigated the geological story of

Terby crater. MOLA altimetry [Smith et al., 1999]

shows that Terby displays an anomalous

morphology compared to other impact crater of

~200 km in diameter. Instead of a circular

depression with a central peak, it displays an inner

flat topography locally eroded. The good spatialresolution (few m to 100m/pixel) of MOC [Malin et

al., 1998], HRSC [Neukum et al., 2004; Jaumann et

al., 2007] and THEMIS [Christensen et al., 2003]

images improves the geomorphic analysis of

geological features. In addition, the stereo HRSC

images allow to generate a Digital Elevation Model

(DEM) in the central N-S strip of Terby, using the

photogrammetric software developed both at the

DLR and the Technical University of Berlin

[Scholten et al., 2005], with a spatial resolution of

15m/pixel, and vertical accuracy of 6.1 m. The

spectral data acquired by the imaging spectrometer

OMEGA [Bibring et al., 2005] give information

about the mineralogy of the surficial centimetric

layer.

The northern inner part of Terby crater displays

a 2 km thick series of layers which the THEMIS IR

images (100 m/pixel) show that the flat top consists

of a 100 m thick gray layer covering a series of

bright layers in alternance with dark layers. The

visible THEMIS images (18m/pixel) allow to show

that bright layers are sub-horizontal with a constant

thickness of few meters. At the same scale

(15m/pixel), the HRSC nadir image allows to

observe the central part of Terby without problemrelated to the mosaic of images: Layers show a

progressive variation of dips from rim to reach sub-

horizontal dip in the center of Terby crater. The

mosaic of 87 MOC images (1.5 to 6 m/pixel) shows

the detailed geometry of the bright layers. Locally,

they are disturbed by stratigraphic unconformities

between which bright layers exhibit a ~5 dip

southward. At a greater scale, the HIRISE images

allow to observe the recent degradation of bright

layers, with aeolian erosive flutes and yardangs in

several directions, and fracture networks due to

temperature varitions. In addition, some layers are

covered by black dunes. During the two first years

of European mission, the OMEGA spectrometerobserved Terby crater three times at high resolution,

(~300m/pixel, orbits #232, 2316 and 2327). These

orbits display broad absorption band characteristic

of pyroxene signature. Their spatial distribution

corresponds to the flat floor of depression, some

parts of plateau and localized areas on bright layers

corresponding to black dunes observed in HIRISE

images. Only the orbit #232 displays subtle

absorption bands at 1.9 and 2.3 m in very localized

areas. The 1.9 m absorption band indicates that

material would be hydrated and its combination

with the 2.3 m drop would be consistent with

hydrated mineral, e.g. phyllosilicates [Poulet et al,

2005], which would be in good agreement with the

geomorphic analysis [Ansan et al., 2005].

This suggests that bright layers could correspond

detritic sediments eroded by strong winds, and

locally covered by black dunes of pyroxenes.

References: Ansan, V. et al (2005) LPSC XXXVI,

Abstract#1324. Bibring, J-P. et al. (2005) Science, 307,

1576-1581. Christensen, P. R. et al. (2003) Science, 300,

2056-2061. Jaumann, R et al. (2007) PSS

55,doi:10.1016/j.pss.2006.12.003. Malin, M. C. et al.

(1998) Science, 279, 1681-1685. Neukum, G. et al. (2004)

ESA Special Publication. SP-1240. Poulet, F. et al.,(2005) Nature doi:10.1038. Scholten, F et al. (2005).

Photogram. Eng. Remote Sens. 71 (10), 1143-1152. Smith

et al. (1999) Science, 284, 1495-1503.