Aeronomy of the Current Martian Atmosphere

Magnetofossils from Ancient Mars: a Robust Biosignature in the Martian Meteorite ALH84001

“…In ALH84001 carbonate, magnetite is distributed throughout the carbonate with widely different abundances and with a fine spatial heterogeneity inconsistent with thermal decomposition (57). A considerable decrease in volume occurs during the conversion of Fe-bearing carbonate ( ϭ 3.96 g/cm 3 ) to magnetite ( ϭ 5.15 g/cm 3 ), and while some magnetites appear to be associated with void space, the majority are not. Impure ALH84001 magnetites containing minor to trace amounts of Al and/or Cr are dispersed among chemically pure magnetites (57).…”

“…More recent surface features (Ͻ1 million years) suggest that liquid water may have flowed out of surficial depths and may still be present relatively close to the Martian surface (42,43). Mars has an atmospheric surface pressure that is 2 orders of magnitude less than that of Earth (3,50). Its atmosphere consists of about 95.3% CO 2 , 0.13% O 2 , 2.7% N 2 , and 1.6% Ar; the remainder is smaller amounts of CO, H 2 O vapor, and trace gases (3,40,50).…”

The Mars thermosphere-ionosphere: Predictions for the arrival of Planet-B

“…Temperatures peak at 333 K in the Southern polar day, and are a minimum at 136 K in the Northern polar night. Mid-afternoon temperatures (LT = 15) at the subsolar latitude reach about 310-320 K, near the lower limit of those estimated from Mariner 6-7 airglow observations (315-350 K) (see Barth et al, 1992). This large day-night temperature gradient gives rise to a pressure gradient which drives global winds which diverge from a point in the midlatitude Southern hemisphere (near LT = 15) and converge near the morning terminator in the mid-latitude Northern hemisphere.…”

“…Solar cycle, seasonal, and orbital variations of the Mars upper atmosphere are indeed expected and generally observed (Stewart and Hanson, 1982;Stewart, 1987;Bougher et al, 1990;Barth et al, 1992). Missions at or near solar minimum (Mariner 4, Viking) have yielded dayside temperatures (140-240 K) that are about a factor of 1.5-2.0 smaller than temperatures (260-350 K) obtained by missions at or near solar maximum (Mariner 6, 7 and 9) (see Barth et al, 1992). Nightside thermospheric observations are presently lacking.…”

“…Also, several airglow measurements by various spacecraft (Mariner 6,7,9) and descent probe density profiles (Viking 1 and 2, Mars Pathfinder) provide scale heights and inferred temperatures for constraining MTGCM simulations (e.g. Stewart et al, 1972;Nier and McElroy, 1977;Seiff and Kirk, 1977;Barth et al, 1992;Schofield et al, 1997). Solar cycle, seasonal, and orbital behavior of the Mars upper atmosphere has been predicted using this MTGCM model.…”