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Sharon Wilson, Smithsonian Institution

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Sharon Wilson, Smithsonian Institution. Alan Howard, ... Aeolian processes? Unique to this unit. Need more data! Unit 4. Caps layered ridges ... Aeolian Dunes. O ... – PowerPoint PPT presentation

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Title: Sharon Wilson, Smithsonian Institution


1
Terby CraterFirst MSL Landing Site
WorkshopPasadena, CA May 31 June 2, 2006
  • Sharon Wilson, Smithsonian Institution
  • Alan Howard, University of Virginia
  • Jeff Moore, NASA Ames Research Center

2
Terby Crater
  • D 170 km
  • Noachian Leonard and Tanaka, 2001
  • 28S, 287W
  • Diverse suite of landforms
  • Indicative of varying geologic processes
    throughout martian history

3
Justification Interior Deposits
  • Light-toned layers
  • Ridges (gt2.5 km)
  • Trough floors
  • Crater floor exposed on scarps of the moat
    deposit (400m) and crater floor
  • Troughs
  • Moat-like depression
  • Flat Crater Floor
  • Viscous flow features
  • Fan, channels, depressions, scoured caprock,
    landslides

4
Possible Fluvial Evidence In the Landing Ellipse
ridges
Wall rock?
5
Sinuous ridges fluvial or glacial activity
related to formation of moat?
1 km
6
Scientific Objectives
  • Smooth, flat, dust free surface with intermediate
    TI (THEMIS NIR)
  • Ellipse LDs and sinuous ridges on moat floor
  • Drive to sites in moat
  • layered deposits in main ridges and crater floor
    (moat scarp)
  • fluvial features in trough related to erosion of
    LDs
  • access ancient wall rock (?)

7
Layered Deposits
  • Indurated, fine-grained sediment based on
    cliff-forming nature, TI and faults
  • Sub-horizontal bedding units Ansan and Mangold,
    2004 Ansan et al., 2005, 2006, conformable with
    regional slope (1.5 degree dip)
  • Laterally continuous on km scale
  • Beds are massive and scalloped
  • no fine-scale interbedding at MOC scale
  • Hydrated mineral signature (clay or sulfates)
    Ansan et al., 2005 Bibring et al., 2006
  • Late Noachian/Hesperian Ansan et al., 2005
    Millochau Crater by Mest and Crown

8
  • Western Ridge
  • 2.5 km thick layered sequence in N. Terby
  • Layered mounds on trough floor
  • Layered sequence with 4 units identified in each
    ridge

9
  • Layered sequence of 4 units recognized in both
    ridges

10
Characteristics of Units 1 and 3
  • 800 m thick
  • Dark toned layers (50-70 m) interbedded with
    light-toned layers (10-25 m)
  • Low albedo layers residual mantle or
    compositional difference?
  • Very regular thickness of beds
  • Laterally continuous

11
Unit 2
  • Light-toned
  • Some horiz bedding
  • Discontinuous, curved laminations and small-scale
    folding
  • Change in depositional environment
  • Soft sediment deformation? Surge deposits?
    Tectonic activity? Aeolian processes?
  • Unique to this unit
  • Need more data!

12
Unit 4
  • Caps layered ridges
  • Intermediate-toned, massive layer sandwiched
    between distinctive thin, dark-toned layers
  • Dark layers weather non-uniformly into a
    small-scale knobby surface
  • Dark layers more indurated and are either
  • coherent beds that break down along widely
    (multi-meter) spaced fractures or
  • they occur as beds of multi-meter scale clasts

13
Origin of the Layered Deposits
Original Depositional Geometry
14
Original Depositional Geometry
Terby Rim
N
3/4 2 1
  • No evidence of thinning, pinching out or
    steepening of layers
  • No evidence for past lateral obstruction
  • Possible layered ridges across moat depression
  • Layers in ridges likely extended out past the
    center of the crater
  • Possible Scenario Layers in crater floor only
    correlate to lower unit in layered ridge
  • Mechanism to erode back layers and form moat?

15
Possible Origins of the Layered Deposits
Process Problem
Volcanic flows or intrusions Fine grained, repetitive nature, erodable X
Mass wasting Fine grained, repetitive nature, lack of source X
Volcanic Airfall Repetitive nature, consistent thickness, induration of layers, lack of obvious proximal volcanic source. X
Glacial Faults, absence of glacial flow and internal collapse features, layers of regular thickness X
Fluvial Geometry not consistent with prograding fan, lack of course grained material, consistent thickness and no obvious source X
Aeolian Dunes Fine grained, lack of cross-bedding X
Loess Fine-grained, terrain conforming and cliff-forming, need upslope winds, might be rhythmically layered O
Lacustrine Nature, geometry and hydrated signature consistent with deposition in fluid moderated by an environmental cycle such as climate or seasons O
16
Is Terby One-Of-A-Kind?
  • Terby is special, but not unique!
  • Similar morphology in other craters around Hellas
  • Important to discern regional history of
    deposition and erosion

20 km
17
Craters in Circum Hellas with Pits and Layers
Moore and Howard, 2005
18
-3.1 km
-6.9km
  • Possible stands of ice covered lakes based on
    topographic, morphologic and stratigraphic
    evidence

-5.8km
-4.5km
Moore and Wilhelms, 2001
19
Histogram of Elevation Around Hellas
-6.9 km
Moore and Wilhelms
-5.8 km
20
Possible Water Stands
  • -2.1 km, -3.1 km and -4.5 km
  • High elevation related to deposition
  • Low elevation related to erosion?

21
Hellas and surrounding region under water?
- 0.7 km
0.6 km
Elevations correlate to well-developed,
inward-facing scarps
22
Summary
ENGINEERING PARAMETER REQUIREMENT
Latitude 60N to 60S
Altitude 2 km
Landing ellipse radius 10 km
Slopes 3 (2 to 5 km length scale)
Slopes 5 (200 to 500 m length scale)
Slopes 15 (20 to 40 m length scale)
Slopes 15 (5 m length scale)
Rock Height 0.6 m
Load bearing surface Not dominated by dust
EDL winds Steady state horizontal 30 m/s
EDL winds Steady state vertical 10 m/s
EDL wind gusts/variability
Radar Reflectivity
Surface winds lt15 m/s (steady) lt30 m/s (gusts)
23
Summary
  • Size and age of Terby represent a long period of
    martian history
  • Geologic history is complex, but perhaps more
    well-constrained than other craters with ILDs and
    relevant to greater Hellas region
  • Climate-related landforms in Terby indicative of
    potentially hospitable environments making it an
    excellent candidate for MSL
  • Layered deposits consistent with lacustrine
    deposition
  • Presence of hydrated minerals (clay?) might
    indicate an ideal environment for preserving
    organic material
  • Fluvial Features (sinuous ridges, fan, flow
    features) also accessible
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