Mars Orbiter Mission (MOM), the maiden interplanetary mission of ISRO, launched on November 5, 2013 by PSLV-C25 got inserted into Martian orbit on September 24, 2014 in its first attempt. MOM completes 1000 Earth days in its orbit, today (June 19, 2017) well beyond its designed mission life of six months. 1000 Earth days corresponds to 973.24 Mars Sols (Martian Solar day) and MOM completed 388 orbits.

MOM is credited with many laurels like cost-effectiveness, short period of realisation, economical mass-budget, miniaturisation of five heterogeneous science payloads etc. Satellite is in good health and continues to work as expected. Scientific analysis of the data received from the Mars Orbiter spacecraft is in progress.

ISRO has also launched MOM Announcement of Opportunity (AO) programmes for researchers in the country to use MOM data for R&D. The success of Mars Orbiter Mission has motivated India’s student and research community in a big way. Thirty-two proposals were supported under this AO. A Planetary data analysis workshop was also conducted to strengthen the MOM-AO scientist's research interest.

First year data from MOM was released to public on September 24, 2016 through ISSDC website. There are 1381 registered users and 370 GB data has been downloaded.

The Mars Colour Camera, one of the scientific payloads onboard MOM, has produced more than 715 images so far. Mars Atlas was prepared and made available on ISRO website.

MOM went through a communication 'blackout' as a result of solar conjunction from June 2, 2015 to July 2, 2015. Telemetry data was received during most of the conjunction period except for 9 days from June 10-18, during superior conjunction. MOM was commanded with autonomy features starting from May 18, 2015, which enabled it to survive the communication 'blackout' period without any ground commands or intervention. The spacecraft emerged out of 'blackout' period with auto control of the spacecraft systems successfully. This experience had enabled the mission team to program a spacecraft about one month in advance for all operations.

MOM spacecraft experienced the ‘whiteout’ geometry during May 18 to May 30, 2016. A ‘whiteout’ occurs when the Earth is between the Sun and Mars and too much solar radiation may make it impossible to communicate with the Earth. The maximum duration of ‘whiteout’ is around 14 days. MOM spacecraft experienced the ‘whiteout’ during May, 2016. However, MOM is built with full autonomy to take care of itself for long periods without any ground intervention. The entire planning and commanding for the ‘whiteout’ was completed 10 days before the actual event. No commanding was carried out on the satellite in the ‘whiteout’ period. Payload operations were suspended. Fault Detection, Isolation and Recovery were kept enabled, so as to take care of any contingency on the spacecraft. Master Recovery Sequencer was programmed, to acquire the attitude of the spacecraft and ensure communication with earth even in case of loss of attitude. The spacecraft came out of ‘whiteout’ geometry successfully on May 30, 2016 and has been normalised for regular operations.

An orbital manoeuvre was performed on MOM spacecraft to avoid the impending long eclipse duration for the satellite. The duration of the eclipse would have been as long as 8 hours. As the satellite battery is designed to handle eclipse duration of only about 1 Hour 40 minutes, a longer eclipse would have drained the battery beyond the safe limit. The manoeuvres performed on January 17, 2017 brought down the eclipse duration to zero during this long eclipse period. On the Evening of January 17, all the eight numbers of 22N thrusters were fired for a duration of 431 seconds, achieving a velocity difference of 97.5 m/s. This has resulted in a new orbit for the MOM spacecraft, which completely avoided eclipse up to September 2017. About 20 kg propellant was consumed for this manoeuvres leaving another 13 kg of propellant for its further mission life.

Major results from the five scientific payloads on MOM are summarised:

Methane Sensor for Mars (MSM) The Methane Sensor for Mars (MSM) on-board Mars Orbiter Mission (MOM) is designed to measure total column of methane in the Martian atmosphere. It is a differential radiometer based on Fabry-Perot Etalon (FPE) Filters. Emission of methane from Mars in recent times has been detected at few ppb level and is sporadic and random in location. Though MSM could not detect any methane (above its sensitivity limit), it provided excellent reflectance data of Mars surface in the 1.65µm region. With 20 bit resolution and SNR>7000, radiometric performance of MSM is extremely good. It is found that during the last 1000 days of operation radiometric calibration of the instrument remained very stable. Figure 1 gives the reflectance map of Mars generated from reference channel data of MSM which is corrected for radiometric errors and CO2 absorption. This data together with reflectance data derived from three visible spectral bands of Mars Colour Camera (MCC) is useful in studying the mineralogy of Mars surface. MSM data has also been used is altudying the dust and cloud properties of Martian atmosphere. This is the first time a near global albedo map of Mars has been prepared using 1.65 µm wavelength (SWIR region) of EM spectra.

Fig.1 Reflectance map of Mars at 1.65µm derived from reference channel data of MSM This data has been used to estimate the variations in albedo of Mars and it has revealed important information on seasonal changes which result in wind transport of dust (Current Science, 2017, Accepted). Mars Color Camera (MCC) The Mars Color Camera (MCC) onboard MOM has 16 different modes of exposures, aimed at imaging the Mars surface for Morphological / Structural mapping, imaging dynamic events viz. Polar Ice cap, clouds, Dust storms and other opportunistic imaging. Analysis of these payloads have churned interesting results - A) Atmospheric Optical Depth estimation in Valles Marineris using Mars Colour Camera

Atmospheric optical depth (AOD) was estimated through an experiment involving multi-view / multi-optical path length images of Mars Colour Camera (MCC) in the Valles Marineris on Mars. The same was used to determine the pressure scale height of the dust (11.24 km) which is commensurate with the known GSM scale height computation (11.2 -12.1 km) (Icarus, 2016). B) Imaging of far side of Deimos by MCC:

The highly elliptical and eccentric orbit of the MOM mission has provided the unique opportunity to view the far side of Deimos, the farthest of the two natural satellites of Mars. This is not possible by any of the contemporary orbiters on Mars from international mission presently operational in Martian orbit. The same has been proved using orbital simulations, shape models and estimation of the apparent magnitude (14.06) (Planetary and Space Science, 2015). C) Morphology study of Ophir Chasma on Mars using MCC data

Ophir Chasma located in the central Valles Marineris has been imaged by MOM at a high resolution of 19.5 m, a geological map has been prepared, various morphological units have been delineated. The various morphological features like- spur and gullies present prominently on the Chasma walls, ridges which covers the northern depression, layered domes, and dark mineral deposits were mapped. Two types of layered deposits are identifiable and exposed i.e. in the canyon walls (low albedo) & Ophir Mensa (high albedo). D) Types of clouds on various Mons using Mars colour camera

Mars colour camera (MCC) onboard Mars Orbiter Mission (MOM) observed ASTER clouds over Olympus and Elysium Mons, that have unique morphology and sometimes forms rays around the central disk of the Mountain. The Aster clouds are thought to form under weak atmospheric static stability and weak background flow, and are probably related to the local up-slope winds associated with the Mons. These clouds are observed during mid to late northern summer on western side of Olympus Mons (A & B images below).

MCC has also observed Lee-Wave cloud over Ascraeus Mons, Mars. Lee wave clouds are a regular train of clouds aligned orthogonal to the prevailing wind. Mountain waves (lee waves, or gravity waves) result from a parcel of air being forced up due to a topographic high, condensing out as a cloud, then dropping back down (C & D images below) . Other than Lee-wave Clouds, Mars colour camera (MCC) onboard Mars Orbiter Mission (MOM) observed ASTER clouds over Olympus and Elysium Mons, that have unique morphology and sometimes forms rays around the central disk. These clouds are observed during mid to late northern summer (A & B images below).

Fig: MCC-MOM observation of Fig.(A,B) ASTER/flower cloud over Olympus Mons, highest point on Mars; and Fig.(C,D) Lee-Wave clouds over Ascraeus Mons Mars

Besides, the shadow of clouds casted on the Martian surface have also been used to estimate the cloud height and one such patch of cloud is estimated to be at an altitude of about 35-38 km. Which is abode of CO2 clouds (LPSC 2015). E)Automatic extraction, monitoring and change detection of area under Polar Ice Caps on Mars:

Area under Snow/Ice of Mars’ North Polar Cap imaged by MCC during 24th to 26th December 2015 (left image) and 22 January 2016 (right image) showed a decrease in area from 9,52,700 km2 to 6,33,825 km2 due to sublimation of dry ice. Also long term change detection (four decades) was done by comparing snow/ice area from MCC images with Viking images. MCC showed a range 6,33,825 km2 to 9,52,700 km2 during imaging period, while during same imaging season of Viking mosaic (1976 to 1980) showed snow/ice area to be approximately 7,83,412 km2 which is within the range calculated by MCC. Mars Exospheric Neutral Composition Analyser (MENCA) The outermost region of a planetary atmosphere — called exosphere — holds the secrets to the atmospheric escape and evolution. This is the region being explored by Mars Exospheric Neutral Composition Analyser (MENCA) experiment aboard the Mars Orbiter Mission (MOM), which is a quadrupole mass spectrometer based payload, developed at the Space Physics Laboratory of Vikram Sarabhai Space Centre, measuring neutral gases in the mass range of 1 to 300 amu. MENCA has successfully studied the distribution of the major species in the Martian exosphere, which has helped understand the solar forcing on the Martian atmosphere. MENCA has provided the first measurements of the low-latitude evening time exosphere of Mars (Fig.1). The measured abundances of the four major Martian exospheric gases, viz. atomic Oxygen (16 amu), molecular Nitrogen and Carbon-Monoxide (28 amu), and Carbon-Dioxide (44 amu), during December 2014, showed significant orbit-to-orbit variability. These observations correspond to moderate solar activity conditions, during perihelion season (when Mars is closest to Sun) and when MOM’s periapsis altitude was the lowest (~265 km). MENCA observations have shown for the first time that the abundance of Oxygen exceeds that of Carbon-Dioxide at an altitude of ~270 ±10 km, during the perihelion evening hours. This result indicate that the altitude where O/CO2 ratio exceeds 1 is a highly variable, is much different than at noon, and therefore it is an important input for constraining the EUV forcing in the models dealing with upper atmosphere of Mars. From the variation of the abundances of different gases with altitude, the temperature of the Martian exosphere was found to be about 270 ±5 K, during perihelion season.

Fig.1: Distribution of the major species in the Martian exosphere in the local evening sector measured by MENCA in December 2014 Another major result from MENCA is the discovery of 'hot' (suprathermal) Argon in the exosphere of Mars (Fig. 2). The word 'hot' or 'suprathermal' indicates that the atoms are more energetic compared to the thermal population, and hence their kinetic temperatures are higher. The upper limit of Ar number density corresponding to the December 2014 period is ~5 × 10 5 cm −3 (at ~250 km), and the typical scale height is about 16 km, corresponding to an exospheric temperature of around 275 K. However, on few orbits, the scale height over this altitude region is found to increase significantly making the effective temperature greater than 400 K: clearly indicating the presence of suprathermal Argon in the Martian exosphere. The detection of these hot particles has important implications in the context of understanding the energy deposition in the Martian upper atmosphere, and will help understand why the Martian atmospheric escape rates are higher than what was believed previously.

Fig. 2: Schematic of the MOM orbit near periapsis (drawn to scale). The blue dots represent the atmospheric gas atoms and molecures of Mars, while the red ones represent the more energetic (suprathermal) atoms. Thermal infrared Imaging Spectrometer (TIS) The Thermal infrared Imaging Spectrometer (TIS) is one of the five instruments onboard Indian Mars Orbiter Mission (MOM) that measures emitted thermal Infrared radiation while orbiting around Mars in elliptical orbit. TIS is a plane reflection grating based infrared spectrometer which uses an un-cooled micro-bolometer detector operating in 7μm to 13μm wavelength range. Elliptical orbit of MOM provides unique opportunity for scanning of full Mars disk from apoapsis at coarse spatial resolution and site specific surface imaging at high spatial resolution in push broom mode from periapsis. TIS has carried out more than 90 imaging sessions over Martian surface as shown in Fig 1. Observed brightness temperatures were found to be related with surface temperature, emissivity, viewing geometry and atmospheric conditions.

Fig 1. The blue points indicate regions where TIS imaging is carried out A scene-level analysis showed a gradual increase in binned scene-level Brightness temperature (BT) at 10.25 μm with increase in areocentric longitude (Ls). BT were relatively higher during Ls 2600 to 3390 as compared to values during Ls 2040 to 2600. Measurements carried out during higher Sun elevation were found associated with higher BT as compared to observations from low Sun elevation angles for similar viewing geometry as shown in figure 2.

Fig.2 Areocentric longitude vs brightness temperature. Imaging sessions were carried out (a) from apoapsis covering Martian disk and (b) site specific imaging from periapsis. Observed BT from an altitude of 52689 km at 12.75 µm showed warmer Southern hemisphere of Mars (on Ls=210.7 degrees) as compared to northern region. High albedo regions of Arabia terra and Isidis and low albedo region of Syrtis Major as seen in the synchronous image acquired from Mars Colour Camera (MCC) onboard the MOM mission is also shown in figure 3.

Fig 3. Brightness temperature at Ls 210.7 and corresponding MCC image. Imaging in periapsis from the altitude of 386 km near Holden crater on Ls:299.2 degrees showed variation of Brightness temperature from 278K to 291K at 10.25 μm. TIS observations are draped on background of MCC data as ancillary source of information. Emissivity spectra retrieved from TIS observation near Holden crater indicated characteristic dip between 9 to 10 μm showing the basaltic surface associated with atmospheric dust. Above findings from TIS involved detailed physics-based correction procedures including instrument thermal background, atmospheric contribution, solar and viewing geometry etc. Lyman Alpha Photometer (LAP) LAP, one of the five scientific instruments of MOM spacecraft’s payload suite developed at LEOS_ISRO, is the first Indian space-borne absorption gas cell photometer that operates on the principle of resonant scattering and resonance absorption at Lyman-Α wavelengths of Hydrogen (121.567 nm) and Deuterium (121.534 nm) respectively. This type of instrument is best suited to measure the line-of-sight Lyman alpha intensity of Hydrogen and Deuterium and thereby the D/H ratio (Deuterium to Hydrogen ratio) estimation of a planet’s atmosphere. LAP can measure the amount of Deuterium compared to the amount of Hydrogen in Mars exosphere. Till date LAP instrument has been operated on-board successfully for more than 150 times (the 1st operation was carried out on 6th February, 2014 at 09:45:00 UT) during various phases of spacecraft’s journey, namely, cruise-phase, comet-phase (Siding Spring C-2013/A, 19th October, 2014 at 18:27:13 UT), Martian orbit phase (from 30th September, 2014 till date) deep-space observations (6th November, 2014 at 10:19:01 UT) for assessment of payload dark count measurements and stellar source observations (3rd February, 2016 at 14:45:00 UT) to perform on-board photometric calibration. Figure-1 shows the generated radial profiles based on the 1st year’s MOM data. The inset in Fig 1 depicts MOM orbit geometry and LAP line of sight observation during the operation carried out during April 2015 which resulted in maximum Lyman alpha brightness. Figure 2 shows the simulated LAP observational trace covering sun-lit disk and bright limb of Mars. Useful scientific data sets are received and are currently under analysis. Analyzed data so far has revealed successful registration of the Hydrogen Lyman-Α brightness as well as clear Hydrogen Lyman-Α flux absorption signatures of Martian atmosphere. Maximum Lyman-Α response was recorded in the zone very close to the bright limb of Martian disc.

Fig:1. Radial profiles of Hydrogen Lyman-Α measured by LAP

Fig. 2: Simulated LAP observational trace during its Martian Orbit phase operation.