Top 25 TES Science Results From Mars Global Surveyor
Tempe - Oct 4, 2001
A global map of Mars based on data acquired by MGS' TES payload
TES is both an instrument and a technique. The Thermal Emission Spectrometer is a scientific instrument that first flew aboard the Mars Observer spacecraft. Following the loss of that spacecraft, TES was rebuilt and launched along with five of the original seven
Mars Observer instruments aboard the new Mars Global Surveyor spacecraft. The purpose of TES is to measure the thermal infrared energy (heat) emitted from Mars. This technique, called thermal emission spectroscopy, can tell us much about the geology and atmosphere of Mars. TES data will provide the first detailed look at the composition of Mars.
TES science results generally fall into one of four categories: surface mineralogy, polar processes, atmospheric processes, and thermophysical properties of the surface.
Key surface mineralogy results include:
- The mineralogy of volcanic materials varies from basaltic, composed of plagioclase, feldspar, clinopyroxene, olivine, plus/minus sheet silicates, to andesitic, dominated by plagioclase feldspar and high-silica volcanic glass. The basalts occur primarily in the ancient, southern hemisphere highlands, and the andesites occur primarily in the younger northern plains.
- The spectra from dark regions closely match both the spectral shape and contrast of particulate samples of terrestrial rocks.
- No unusual particle size or other environmental effects are observed, nor are required, to account for the spectra observed for Mars.
- Aqueous mineralization has occurred in limited regions under ambient or hydrothermal conditions. Gray, crystalline hematite is found in three locations that are interpreted to be in-place sedimentary rock formations. These units provide evidence for the long-term stability of liquid water near the surface of Mars.
- No evidence for carbonates has been found. Arguments can be made for the failure to detect these minerals, but we can conclude that large-scale (10's of km), coarse-grained (>50 micron) deposits of >~10% carbonates are not currently exposed at the martian surface. This lack of detection is consistent with many models for early Mars in which large volumes of carbonates never formed.
- Olivine has been identified and mapped in specific locations in the basaltic terrains at abundances up to 15-20%.
- Unweathered volcanic minerals (pyroxene, feldspar, and minor olivine) dominate the spectral properties of martian dark regions. Conversely, no evidence has been found for weathering products above the TES detection limit. This lack of evidence for chemical weathering of the martian surface indicates a geologic history dominated by a cold, dry climate in which mechanical weathering was the dominant form of erosion.
- The composition of "White Rock" appears to match that of typical martian dust. Many other unique surfaces remain to be investigated.
Key polar conclusions include:
- CO2 condensation occurs in three forms, fine-grained, coarse grained, and slab ice; the form can change in a few days. Most condensation occurs at the surface, not in the atmosphere. Slab ice is the prevalent form in the outer regions of the forming cap, and persists untiil shortly after seasonal sunrise.
- The interiors of the seasonal caps are characterized by spatially nonuniform behaviour, with several small, unique regions. comparisons with Viking observations indicate little difference in the seasonal cycle 12 martian years later. the observed radiation balance indicates CO2 sublimation budgets of up to 1250 kg m-2.
- For most of the seasonal cap, while kinetic temperatures remain near the CO2 frost point, albedos increase slowly with the rise of the Sun, then drop rapidly as the frost becomes patchy and disappears over a period of ~20 days.
- A "Cryptic" region in the south cap remains dark and mottled throughout its cold period. TES spectra indicate that the Cryptic region has much larger grained solid CO2 than the rest of the cap and that the solid CO2 here may be in the form of a slab. Although CO2 grain size may be the major difference between different regions, incorporated dust is also required to match the observations.
- The Mountians of Mitchel remain cold and bright well after other areas at comparable latitude, apparently as a result of unusually small-sized CO2 frost grains.
- Regional atmospheric dust is common; localized dust clouds are seen near the edge of the cap prior to the onset of a regional dust storm and interior to the cap during the storm.
Key atmospheric science results include:
- The life cycle of five regional dust storms has been observed. These storms have significant impact on the atmospheric temperature structure, increasing the temperature by up to 15 K to several scale heights.
- Direct heating of the atmosphere in one hemisphere can lead to an intensification of the Hadley cell circulation and produce a similar-scale heating of the atmosphere in the opposite hemisphere almost instantaneously.
- The occurrence of water-ice clouds is highly sensitive to atmospheric temperatures, and heating by dust virtually removes water-ice clouds from a large portion of the planet for months.
- Water-ice clouds have a seasonal cycle as distinctive as the dust seasonal cycle. In aphelion (northern summer) season, an equatorial cloud belt is observed between 10 degrees south and 30 degrees north, where upward motion of the Hadley circulation is expected. at all seasons (except during regional dust storms) clouds are common near large topography (Tharsis, Alba Patera, and Elysium).
- The thermal structure of the atmosphere is observed to warm and cool according to season and distance from the Sun. Maximum atmospheric temperatures are found at the south pole at southern hemisphere solstice.
- The Hadley circulation changes from a (nearly) symetrical two-cell configuration at equinox to one cross-equatorial cell at solstice.
- At solstice the steep temperature gradient between the descending branch of the hadley cell and the polar night produces a strong eastward jet of winds or polar vortext with velocities approaching 160 m s-1.
- waves are common throughout the atmosphere and are especially strong in the winter mid-latitudes. zonal wavenumber 2 dominates at lower altitudes while zonal wavenumber 1 becomes stronger at higher altitudes.
Key surface physical property results include:
- A third inertia-albedo mode, corresponding to intermediate inertia and albedo values, has been identified using high-resolution albedo and temperature TES data. This distinct unit is separate from the low-inertia/bright, and high-inertia/dark regions discovered previously. It may consist of a bonded, duricrust unit.
- Localized regions of high inertia (greater than 800 J-m-2-K-1-s-1/2) are identified in TES data. These low-lying surfaces, e.g., channel and crater floors, may have formed by a combination of aeolian, fluvial, or erosional processes, or may be exposed bedrock.
- More results arriving soon...
TES at Arizona State
Mars at JPL
MGS Image Database at MSSS
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Mars Gets A Global Dusting
Tempe - July 23, 2001
Though there has been a fair amount of evidence that the Earth's atmosphere is undergoing global warming, the process is slow enough that there are plenty of skeptics, including some very influential people, who argue that it may not be happening at all.
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