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Mangalyaan: Payload: Methane sensor for Mars

Mangalyaan - Mars Orbiter Mission
In Preparation for Mars Orbit Injection on September 24th, 2014

Payload - Methane sensor for Mars

 


Source: ISRO

Methane is an organic molecule present in gaseous form in the Earth’s atmosphere. More than 90% of Methane on our home planet is produced by living organisms. The recent detection of plumes of Methane in the northern hemisphere of Mars is of great interest because of its potential biological origin. Methane sensor for Mars is one of the scientific instruments of the payload on MOM spacecraft, MSM payload  weighing 2.94 kg is designed to measure amount of Methane of the order of parts per billion (ppbs) in martian atmosphere. MSM is a differential radiometer(radiometer is a device used to measure temperature of cosmic background) based on Fabry Perot Etalon (FPE) filters. MSM maps the source and sinks of Methane by scanning the full Martian disc from apogee position of Mars Orbiter.


Differential microwave radiometer:

 

Image credit: NASA

Scientific investigations:

         Image source:   www.defianceofscience.com


By correlating the temporal and spacial variation of methane with other geophysical parameters, it may be possible to find out more about the processes, biotic or abiotic which determine the dynamics of Methane cycle within the Martian atmosphere and ultimately solve some of the interesting things about the existence of life forms in Mars.

 

Image source :  NASA

 

Sensor configuration:
Fabry-perot Etalon sensor consists of two channels - Methane channel, reference channel. Fore-optics collects radiance from the sense and focuses it onto a field-Stop. Diverging beam from the field stop is collimated and then divided into two parts by a beam filter. One part of the beam transmits through FPE filter of methane channel whereas the other part transmits through FPE filter of reference channel and then focused onto respective focal planes. InGaAS photo divider are used as photo detectors. InGaAs or indium gallium arsenide is an alloy of gallium arsenide and indium arsenide. As gallium and indium belong to Group III of the Periodic Table, and arsenic and phosphorous belong to Group V, these binary materials and their alloys are all III-V compound semiconductors (InGaAS Photo detectors are sensitive to wavelength over a wide spectral range and are available as image sensors, and has applications in optoelectronic technology.)


InGaAS photo detector:

 

Fabry-Perot Etalon sensor optical configuration

Image source : NASA


An FPE filter transmit optical radiation at regular intervals of frequency. FPE filter used in methane channel and reference channels are exactly similar. But FPE filter of reference channel is tilted by about 1 degree with respect to the optical axis so that its transmission peaks are slightly shifted. Transmission bands of first Etalon exactly coincide with the absorption lines of methane  where as transmission peaks of reference Etalon are positioned in between the gaseous absorption lines where absorption is nil.

Image source: NASA


Technique used to determine concentration of methane:
Radiance measured in methane channel varies with Methane  concentration in the atmosphere where as that of reference level is insensitive to it. So, the differential signal gives a Measure of methane in the atmosphere. Based on this technique, Methane concentration on Martian atmosphere is determined. 


Conclusion:
The previous rover missions to Mars reported that the Red Planet’s atmosphere contained Methane and that its concentrations depend on seasonal fluctuations. NASA’s rover has come up empty-handed in its search for Methane in the atmosphere of Mars, during 8 months of data collection, the rover detected average Methane concentrations of 0.18 parts per billion. The researches say that, because of the measurement’s margin of error, the finding translates to essentially no methane in Martian atmosphere.


Let us hope for the success of Mangalyaan , MSM, through which we can ultimately determine the dynamics of Methane cycle within the Martian atmosphere and ultimately solve some of the interesting things about the existence of life forms in Mars.

 

 

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Author
Ms. Manasa Perikala

IIT-Varanasi

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