Thermal and visible studies of Mars using the Termoskan data set
<p>In February and March, 1989, the Termoskan instrument on board the Phobos '88 spacecraft of the USSR acquired the highest spatial resolution thermal data ever obtained for Mars, ranging in resolution from 300 m to 3 km per pixel. It simultaneously obtained broad band visible channel...
| Summary: | <p>In February and March, 1989, the Termoskan instrument on board the Phobos '88
spacecraft of the USSR acquired the highest spatial resolution thermal data ever obtained
for Mars, ranging in resolution from 300 m to 3 km per pixel. It simultaneously obtained
broad band visible channel data. The panoramas cover a large portion of the equatorial
region from 30°S to 6°N. New and unique analyses facilitated by Termoskan are
presented here. In addition, this thesis describes the instrument, data, and validation.
Termoskan thermal data shows good temperature agreement with Viking IRTM.
However, conversion of Termoskan visible data to bolometric albedo is problematic. </p>
<p>Utilizing the Termoskan data, I recognized a new feature on Mars: ejecta blanket
distinct in the thermal infrared (EDITH). Virtually all of the more than 100 such features
discovered in the Termoskan data are located on the plains near Valles Marineris. I
compiled a data base of 110 EDITH and non-EDITH craters ranging in diameter from 4.2
km to 90.6 km. EDITHs have a startlingly clear dependence upon terrains of Hesperian
age, and show almost no other correlations within the data base. The Hesperian terrain
dependence cannot be explained by either atmospheric or impactor variations. Wind
patterns or locally available aeolian material cannot provide a single overall explanation for
the observed variations. I postulate that most of the observed EDITHs are due to
excavation of thermally distinctive Noachian age material from beneath a relatively thin
layer of younger, more consolidated Hesperian volcanic material. The plausibility of this
theory is supported by much geological evidence for relatively thin near-surface Hesperian
deposits overlying massive Noachian megabreccias on the EDITH-rich plains units. I
suggest that absence of thermally distinct ejecta blankets on Noachian and Amazonian
terrains is due to absences of distinctive near-surface layering. 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. </p>
<p>Also included in the thermal images are observations of several major channel and
valley systems including significant portions of Shalbatana, Ravi, Al-Qahira, and Ma'adim
Valles, the channel south of Hydraotes Chaos, channel material in Eos Chasma, and small
portions Simud, Tiu, and Ares Valles and channel material in Gangis Chasma.
Simultaneous broad band visible data exists for all but Ma'adim Vallis. I find that most of
the channels and valleys have higher inertias than their surroundings, consistent with
previous thermal studies of martian channels. I show for the first time that thermal inertia
boundaries closely match all flat channel floor boundaries. Using Viking albedos,
Termoskan temperatures, and thermal modelling, I derive lower bounds on typical channel
thermal inertias ranging 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.
Atmospheric and geometric effects are not sufficient to cause the inertia enhancements. 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. Small scale aeolian deposition or aeolian deflation may, however, play some
role in the inertia enhancement Channel floor inertia enhancements are strongly
associated with channels showing fretted morphologies such as wide, flat floors and steep
scalloped walls. 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 may have been preferentially present due
to the low, flat fretted floors may have enhanced bonding of original fines or dust fallout
The coupling of both EDITHs and channel inertias to morphology is unlike most sharp
Martian inertia variations which are decoupled from observed surface morphology. </p>
<p>Termoskan observed morning limb brightening 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 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. Localized high altitude
stratospheric clouds are observed in the visible channel. </p>
<p>The Termoskan data show that the highland-lowland boundary in the Aeolis
Quadrangle appears strongly correlated with a high-low thermal inertia boundary. The
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. Several
other large scale thermal boundaries are also observed in the data. </p>
<p>Termoskan observed fine thermal structure on the flanks of Arsia Mons and
elsewhere, which represent examples of interesting and significant thermal variations seen
at the limit of Termoskan's spatial resolution. Sharp variations and boundaries imply there
cannot be global scale dust blanketing deeper than about one centimeter, if that. </p>
<p>Termoskan obtained the first ever thermal images of Phobos' shadow on the
surface of Mars, along with simultaneous visible images. The best observed shadow
occurrence was on the flanks of Arsia Mons. For this occurrence, I combined the
observed decrease in visible illumination of the surface with the observed decrease in
brightness temperature to calculate thermal inertias of the Martian surface. Most of the
derived inertias fall within the range 0.9 to 1.4, corresponding to 5 to 10 micron dust
particles for a homogeneous surface. Dust at the surface is consistent with previous
theories of Tharsis as a current area of dust deposition. Shadow derived inertias are
sensitive to mm depths, whereas diurnally derived inertias are sensitive to cm depths. The
shadow derived inertias are very similar to Haberle and Jakosky [1991] atmospherically
corrected Palluconi and Kieffer [1981] Viking IRTM diurnally derived inertias. Thus, if
near surface layering exists at all in this region, it is not very significant.</p>
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