DN VALUE (INFRARED)
7.1 Summary of Major Conclusions
Chapter 7
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And, while with silent, lifting mind I've trod The high untrespassed sanctity of space, Puc out my hand, and touched the face of God.
-John Gillespie Magee, Jr.
SUMMARY OF CONCLUSIONS, AND THE FuTURE
This chapter presents a summary of the major thesis conclusions and some implications and proposed studies for future missions. The major thesis conclusions are presented in Section 7 .1. Discussion of the future is split into proposed future Termoskan research (Section 7 .2) and implications and proposed studies for Mars Observer (MO), Mars '94 (M94), and other future missions (Section 7.3). This latter section includes a set of proposed sites originally selected for intercomparison of Mars Observer instrument data, but which will be useful for any future mission where orbital data sets are intercompared. Also included are proposed studies designed originally for Mars Observer and proposed studies for Mars '94 and other future missions. Much of the MO material was prepared before the tragic loss of MO. I still include a reduced form of this material because it should be useful for whatever analogous instruments fly on future missions.
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observations bode well for future instruments such as Termoskan 2 on Mars '94 and instrwnents that resemble the thermal emission spectrometer on MO.
Comparison of Termoskan thermal data with Viking IRTM data shows good agreement between the two. Thus, Termoskan temperature data should be quite adequate for determination of thermal inertias. Conversion of Termoskan visible data to bolometric albedo is problematic, however. Fortunately, qualitative thermal and visible analyses, quantitative thermal inertia determinations tied to Viking albedos, analyses of atmospheric profiles, and analysis of the shadow of Phobos on Mars have all yielded interesting new conclusions about Mars. The major conclusions are summarized here.
I have recognized a new feature on Mars: ejecta blanket distinct in the thermal infrared (EDITH). EDITHs have a startlingly clear dependence upon terrains of Hesperian age. They show no consistent correlation with any other factor. I postulate that EDITHs exist on the observed Hesperian units because of impact excavation into a thick, more fragmented, materially different Noachian layer beneath a relatively thin younger layer or layers of Hesperian volcanic material. I suggest that absence of thermally distinct ejecta blankets on Noachian and Amazonian terrains is due to absences of distinctive near-surface layering. I also postulate that EDITH variations are primarily controlled by the degree of excavation of the Noachian layer. However, secondary effects such as degree of erosion of the blankets or local availability of aeolian material probably cause some thermal variations. The thermally distinct nature of the blankets probably results from the ejecta itself, or possibly from secondary aeolian deposits preferentially trapped on the blankets. Thermally distinct ejecta blankets are excellent locations for future landers and remote sensing because of relatively dust free surface exposures of material excavated from depth.
Termoskan observed several channel and valley systems on Mars at the highest spatial resolution ever. I find that most of the channels and valleys have-higher inertias than their surroundings, consistent with previous thermal studies of martian channels. I
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show for the first time that thermal inertia boundaries closely match all flat channel floor boundaries. Lower bounds on typical channel thermal inertias range from 8.4 to 12.5 (10-3 cal cm-2 s-1/2 K-1). Lower bounds on inertia differences with the surrounding heavily cratered plains range from 1.1 to 3.5.
I agree with previous researchers that localized, dark, high inertia areas within channels are likely aeolian in nature. However, thermal homogeneity and strong correlation of thermal boundaries with the channel floor boundaries lead me to favor non- aeolian overall explanations, in contrast with some IRTM researchers. Small scale aeolian deposition or aeolian deflation may play some role in the inertia enhancement Flat floors and steep scalloped walls are observed in most regions that show increased inertia.
Therefore, I favor fretting processes over catastrophic flooding for explaining the inertia enhancements. Fretting may have emplaced more blocks on channel floors or caused increased bonding of fines due to increased availability of water. Alternatively, post- channel formation water that was preferentially present due to the low, flat fretted floors may have enhanced bonding of original fmes or dust fallout Also of interest, buttes within channels have inertias similar to the plains surrounding the channels. Thus, the buttes were likely part of a contiguous surface prior to channel formation.
Termoskan observed morning and evening limbs of Mars. Morning limb brightening is observed in the thermal channel, but not in the visible channel. The thermal morning limb brightening is likely due to a water ice or dust haze that is warmer than the surface at the time of the observations. A water ice or dust haze with a scale height of 5 km could match the observations. Visible scattering is observed to be significant on morning and evening limbs out to 60 or 70 km. In addition, localized high altitude stratospheric clouds are observed in the visible channel. They may correspond to those detected by the Phobos '88 Auguste experiment
The Termoskan data show that highland-lowland boundary in the Aeolis Quadrangle appears strongly correlated with a high-low thermal inertia boundary. The
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sharpness of that boundary varies from less than 4 km to more than 50 km. In all cases, inertias continue to decrease gradually for many tens of km into the lowlands.
Termoskan observed fine thermal structure on the flanks of Arsia Mons and elsewhere. On Arsia Mons the structure apparently correlates with lava flow units. The cause may be primary or secondary, with secondary causes favored in this thesis. This structure is just one example of interesting and significant thermal variations seen at the limit of Termoskan's spatial resolution. The associated boundary and other sharp large scale boundaries are often sharp down to the limit of Termoskan's resolution. These variations and boundaries, including in the very low thermal inertia Arsia Mons region, imply that a uniform dust layer thicker than about one em cannot exist
Termoskan obtained the first ever thermal images of Phobos' shadow on the surface of Mars. Simultaneous visible images were also obtained. I analyzed an occurrence of the shadow on the flanks of Arsia Mons. I combined the observed decrease in visible illumination of the surface with the observed decrease in brightness temperature to calculate thermal inertias of the uppermost tenths of a millimeter of the Martian surface.
Most of the derived inertias fall within the range 0.9 to 1.4. These inertias correspond to dust with particle sizes of 5 to 10 microns for a homogeneous surface. The presence of dust at the surface is consistent with previous theories of the Tharsis region as a current area of dust deposition. Viking IRTM derived inertias are diurnally derived and are sensitive to centimeter depths, whereas the shadow derived inertias sample the upper tenths of a millimeter of the surface. The shadow derived inertias are significantly lower than those originally derived from Viking IRTM measurements (2 to 3.5) [Palluconi and Kieffer, 1981]. However, they are very similar to Haberle and Jakosky's [1991]
atmospherically corrected Palluconi and Kieffer [1981] inertias. Thus, if layering exists at all, it is not very significant
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