Mars Polar Layered deposits' Observations from the THEMIS investigation

1
Mars Polar Layered deposits. Observations from
the THEMIS investigation
??????????? ???????? ???????? ?????????.
???????????? ?????? ??????? THEMIS.

• Anton B. Ivanov, THEMIS team
• JPL
• HEND Workshop, IKI

?. ?. ??????, ??????? THEMIS ???????????
??????????? ???????? HEND Workshop, ???
2
Polar research and THEMIS

• What is the composition, structure and chronology
  expressed in the stratigraphy of the polar
  deposits?
• Thickness, extent, and continuity of layers.
• Composition, structure, and ice- and dust-grain
  characteristics of layers.
• History and origin of the re-entrant troughs
• Seasonal behavior of surface seasonal and
  residual ice caps.

After results of the First Polar Conference
(Clifford et al.2000)
3
Polar caps the MOLA view
North Pole to 54N
South Pole to 54S
4
Polar caps the MOLA view
5
THEMIS Characteristics

• THEMIS as spectrometer
• usability for polar observations, note cold
  spots
• T11, T20, T25, (Kieffer/Titus (TES/IRTM), Forget
  (IRTM) )
• THEMIS as a imager
• THEMIS context - MOC WA/Viking - THEMIS - MOC NA

6
THEMIS IR bands
THEMIS Calibration report. Figure 7-6
THEMIS IR camera has 10 bands from 6.62 µ m to
14.96 µm Band 9 (12.58) is the most useful for
polar studies.
7
THEMIS sensitivity
Band 9 gain8 offset 4

• This graph illustrates change in degrees K per 1
  DN at a range of surface temperatures

8
Mars South Pole - Overview
9
South pole - exposed water ice
H. Kieffer, T. Titus (2002)
10
South pole - Swiss cheesenote temperatures on
the bottom of the depressions
Temperature, K
MOC-NA
THEMIS IR
THEMIS VIS
11
North and South layered deposits
South polar layers
North layers
THEMIS VIS, 36 m/pixel, still covered by seasonal
frost (early spring)
MOC-NA, 5 m/pixel, not covered with frost. NP
Summer
12
Matching layers. Figure shows 3 MOC images taken
in various parts of the cap (100km distance).
It is possible to find matches for some layers.
Work is currently under way to map these matches
in 3D.
13
MGS/Odyssey data analysis.
Excellent geometrical information allows us to
register MOC-NA images together with THEMIS VIS
images (see Figure). THEMIS gives a lot of
coverage (e.g. we have already covered South Pole
_at_ 36 m/pixel), where as MOC-NA gives us
phenomenal detail. We plan to have a more active
campaign next Mars summer to cover more of the
North Pole.
14
THEMIS IR at the Pole.
Figure illustrates two THEMIS IR images taken on
different orbits (10 deg of Ls apart) of the
same trough in the NPLD. Temperature of the
layers of the trough changes at a different rate
from the rest of ice. Measure of this rate is
important to understand thermophysical properties
of the layers.
15
Summary

• THEMIS contributes new types of data IR at
  100m/pix and VIS at 18m/pix
• THEMIS is capable of tracking changing properties
  of the water ice on the surface.
• Hypothesis was the extent of the ancient ice
  cap similar to current or it was covering a much
  larger area.
• Joint analysis of THEMIS VIS and MOC NA images
  allows to locate similar (same texture and
  position) layers in various places on the cap.
• Tracing 3D layer structure will show how the cap
  was developing with time.

16
Summary - cont.

• THEMIS IR has enough SNR to analyze rate of
  temperature change of layers in the trough. We
  are investigating possibility of calculating
  thermal inertia properties of the terrain.
• The amount of dust/ice ratio in the polar layered
  deposits is still unknown.
• Question Is it possible to use HEND/GRS data to
  constraint this ratio and obtain some bulk number
  for both north and south ice caps.