Mars Polar Layered deposits. Observations from the THEMIS investigation

Anton B. Ivanov, THEMIS teamJPLHEND Workshop, IKI

Марсианские полярные слоистые отложения. Спектральная съёмка камерой THEMIS.

А. Б. Иванов, команда THEMISЛаборатория Реактивного Движения HEND Workshop, ИКИ

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])

Polar caps – the MOLA view

North Pole to 54N South Pole to 54S

Polar caps – the MOLA view

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.

THEMIS sensitivityTHEMIS Sensitivity to change in

DN for various temperatures

0

2

4

6

8

10

12

14

16

18

140 160 180 200 220 240 260

Temperature

DK

/DD

N

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

Band 9gain=8offset =4

Mars South Pole - Overview

South pole - exposed water ice

H. Kieffer, T. Titus (2002)

South pole - Swiss cheesenote temperatures on the bottom of the depressions

Tem

pera

ture

, K

THEMIS VIS

MOC-NA

TH

EM

IS IR

South polar layers

North and South layered deposits

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

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.

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 @ 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.

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.

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.

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.