THEMIS spectral unit mosaics

1
THEMIS spectral unit mosaics
Olivine (0-0.10)
Basalt 1 (0-1.3)
Blackbody dust (0 to 1.0)
RMS Error (0-0.01)
Nili trough
2
THEMIS spectral endmembers

• Dust and blackbody distributions represent
  varying surface spectral contrast due to either
  varying contribution from dust or to varying
  particle size/surface texture
• Basalt 1 surface is intermediate between TES
  Surface Types 1 and 2
• Basalt 2 surface is similar to Surface Type 1

Nili trough
3
TES analysis of THEMIS spectral units
Modeled abundances Basalt 1 Feldspar 32 /- 5
Pyroxene 26 /- 5 Olivine 6 /- 2
High-silica 20 /- 4 Other 17 Basalt
2 Feldspar 33 /- 4 Pyroxene 29 /- 5 Olivine
9 /- 3 High-silica 15 /- 5
Other 13
High-silica phases silica glass, opal,
zeolite, clay (cannot reliably distinguish these)
Other carbonate, sulfate, hematite,
amphibole, quartz (individually modeled at 0-9,
below det. limits)
Nili trough
4
Spectral ratios basalt 2/basalt 1

• Mineral abundances are not significantly
  different between models of basalt 1 and basalt 2
• However, spectral ratios over these surfaces
  confirm that spectral differences may be
  primarily attributed to olivine abundance

5
TES dust cover index

• lt0.95 high dust cover
• gt0.97 low dust cover
• Refer to Ruff and Christensen 2002 for details
  about the index
• Values in proposed ellipse range from 0.96 to
  1.0, indicating moderate to low dust cover
  relative to classic high-albedo regions

Nili trough
6
TES 465/530 indices

• 465 cm-1 feature is present in clays, zeolites,
  amorphous silica, silica glass
• Features near 530 cm-1 present in olivine,
  pyroxene, and some clays
• High values of both features indicative of
  smectite clays Ruff and Christensen, 2007
• In Nili Fossae region, high 530 index features
  primarily due to high pyroxene and olivine
  concentrations

• Phyllosilicates observed by CRISM are not
  clearly detected with TES 465/530 indices
• could be attributed to low abundance or
  texture/particle size effects
• presence of high pyroxene and olivine in the
  region may also confound phyllosilicate detection
  with index method

Nili trough
7
TES combined 465 530 indices

• One orbit found where ratio high/low 465/530
  indices shows evidence of smectite doublet

Nili trough
8
TES combined 465 530 indices

• However, the 530 feature is co-located with CO2
  hot band at 535 cm-1
• The other hot band at 788 cm-1 is also observed
  in the ratio
• Suggests that the 530 portion of the doublet is
  actually due to residual CO2 in the ratio
• Phyllosilicate detection in this example is
  ambiguous

Nili trough
9
Summary

• Two units identified in THEMIS data (in addition
  to dust) basalt 1 and basalt 2 - both
  contain significant high-silica phases, which are
  probably alteration products
• Units are distinguished primarily by olivine
  abundance.
• Phyllosilicates observed by CRISM are not clearly
  detected with TES 465/530 indices
• could be attributed to low abundance or
  texture/particle size effects
• Presence of high pyroxene and olivine in the
  region may also confound phyllosilicate detection
  with index method
• TES dust cover index values within ellipse are
  moderate-to-high compared to classic high albedo
  regions, indicating moderate-to-low dust cover