Observation of suprathermal argon in exosphere The Mars Exospheric Neutral Composition Analyser (MENCA) reported altitude profiles of
argon-40 in the Martian
exosphere from four orbits during December 2014 when the
periapsis of the spacecraft was lowest. The upperlimit of the argon
number density corresponding to this period is almost 5 × 105/cm3 at an altitude of 250 km and the typical
scale height is around 16 km corresponding to an exospheric temperature of around 275 K. However, on two orbits, the scale height over this altitude region is found to increase significantly making the effective temperature greater than 400 K. The observations of Neutral Gas and Ion Mass Spectrometer (NGIMS) onboard the
MAVEN also indicate that the change in slope in argon density occurs near the upper exosphere of around 230–260 km. These observations indicate significant suprathermal populations of
carbon dioxide and argon in the Martian exosphere.
Global apparent short wave infrared albedo mapping Global apparent
short wave infrared (SWIR)
albedo mapping of Mars was executed based on data acquired from the Methane Sensor for Mars (MSM) payload. The instrument is a differential radiometer in SWIR region of spectrum that measures reflected
solar radiance in two SWIR (1.64 to 1.66 μm) channels. The first one is a methane channel which measures the absorption by methane and second one is a no absorption channel (reference channel). The reference channel data acquired from October 2014 to February 2015 was used for apparent SWIR albedo mapping. Data less than one degree of the limb of the planet was discarded to avoid atmospheric limb brightening and to ensure that the field of view was entirely on the planet. Data with incidence and zolar
zenith angle greater than 60° was also discarded to reduce atmospheric effects. The bright regions having an albedo greater than 0.4 are mainly localised over the
Tharsis plateau,
Arabia Terra, and
Elysium Planitia and generally represent surface covered by dust while the low albedo of less than 0.15 are mainly localised over
Syrtis Major Planum,
Daedalia Planum,
Valles Marineris and
Acidalia Planitia. The low albedo is associated with dark surfaces having volcanic rock basalt as surface expostures. Weekly mean apparent albedo data over
Syrtis Major Planum was recorded in a period of solar longitudes 205 to 282 (October 2014) during which dust activities are significant. A surge in mean albedo from the usual 0.2 to an erratically higher near 0.4 was recorded on solar longitude 225 which was possibly due to the local injection of dust into atmosphere.
Neutral composition of evening time exosphere The Mars Exosphere Neutral Composition Analyser (MENCA) during 18–29 December 2014 provided altitude profiles of three major constituents;
carbon dioxide (amu 44),
nitrogen molecule &
carbon monoxide (amu 28) and
atomic oxygen (amu 16) in the Martian exosphere. This measurents were taken from four orbits which were closest to Mars with a
periapsis which varied from 262–265 km during the evening time or close to sunset terminator hours to attain moderate solar activity conditions. During evening hours the carbon dioxide density changes from 3.5 × 107 cm to 1.5 × 105/cm3 for an altitude change of 100 km in the exosphere. The number density of amu 28 is comparable to that of carbon dioxide (amu 44) at lower altitudes and exceeds above 275 km. The factor becomes almost 10 at 375 km. The atomic oxygen number density exceeds that of carbon dioxide above 270 km. At 335 km, this difference becomes a factor of 10, above which atomic oxygen far exceeds the abundance of carbon dioxide. The transition from carbon dioxide to atomic oxygen dominant exosphere is an important indicator of the solar
EUV forcing. The mean exospheric temperature derived using the
scale height values estimated from the observed
partial pressure variation in the three mass channels is 271 ± 5 K. These first observations corresponding to the Martian evening hours is expected to provide constraints data to the thermal escape models.
Radio occultation experiment on solar corona Radio occulation experiments were performed using
S-band downlink signals from the spacecraft during the May–June 2015 (post-maxima of solar cycle 24) period when the Sun was between Earth and Mars along a line in the same elliptical plane. The downlink signals from the spacecraft of frequency 2.29 GHz passed through the solar
coronal region at solar offset distances between 4–20
solar radius. The
Chandrayaan-2 orbiter and the Mars Orbiter Mission orbiter would also conduct a joint series of Radio occultation measurements of each other's signals. This was used by mission scientists to analayse the lunar and solar wind plasma environments.
Atmospheric optical depth in the Valles Marineris Stereo images of
Valles Marineris acquired by Mars Colour Camera (MCC) payload along with the co-registered
MOLA Digital Elevation Map (DEM) were used to calculate atmospheric
optical depth (AOD) over northern and southern walls of Valles Marineris. On northern wall ranging from 62°W to 68°W, the
red channel of MCC measured an AOD of 1.7 near the bottom of the valley and decreases
monotonically to about 1.0 near the top, while the green channel measures an AOD of around 2.1 and similarly decreases monotonically with increasing altitude. Both measurements shows a clear relation that can be well fitted with an
exponential curve. The calculated scale height of AOD equals to 14.08 km and 11.24 km for red and green channels respectively. The red channel AOD measurement on the southern wall of Valles Marineris ranging from 62°W to 68°W remains nearly steady from 1.75 in the bottom of the valley to 1.85 near to the top and does not show a monotonic decline of AOD with altitude. From the AOD map overlaid on MCC image draped on MOLA DEM, it is clear that there is a mountain-like structure along the southern walls of the valley, which is expected to cause the creation of banner clouds in the lee side of the mountain or
lee wave clouds. The AOD variation with altitude along the southern wall between the longitudes 57°W to 62°W where mountain structures are not present shows a normal monotonic decrease. This further supports the existence of lee wave clouds on the southern wall of Valles Marineris around 65°W. ==Status==