Discuss the role of mineralogical evidence in the search for past habitability on Mars.

Mars today is cold and dry, so any habitable past it had survives mainly in its rocks. Some minerals form only in the presence of water. They act as a geological archive of where water existed, what its chemistry was, and whether traces of life could have been preserved. This makes mineralogy central to the search for past habitability.

Minerals as records of past water

• Hydrous sulphates such as gypsum and melanterite form through water–rock interaction, so finding them marks past water activity [1].
• Melanterite forms when the sulphide mineral marcasite oxidises. It points to short-lived wet, acidic, oxidising conditions, so it reveals the water's chemistry as well as its presence [1].
• Gypsum records past water and can preserve biosignatures within its mineral structure, which makes it a priority target for sampling [1].

Reading the evidence: orbit versus ground

• Orbiters map minerals over wide areas, but orbital data alone cannot fully characterise Martian minerals; precise measurement on the ground is needed [1].
• A laser Raman spectrometer reads each mineral's distinct "spectral fingerprint", which allows confident identification at the site [1].
• Minerals that record water and preserve biosignatures help mission planners choose landing and sampling sites [1].

Terrestrial analogues: India's contribution

• With DST-FIST support, a University of Kerala team identified melanterite at Neyveli and gypsum in the Tiruchirappalli Badlands and the Atacama Desert. The team proposed all three as Martian analogue sites [1][2].
• These mineral analogues complement ISRO's HOPE station in Tso Kar, Ladakh. HOPE is a habitat analogue, chosen for its high UV, low air pressure, extreme cold and saline permafrost [3].
• Mangalyaan was an orbiter [4], so reference data like this would matter most for a future Indian lander.

Limitations

• Habitable is not the same as inhabited: these minerals show that conditions once suited life. They do not prove that life existed [1].
• The analogues are imperfect: the Tamil Nadu sites are warm and at Earth's air pressure. They model how the minerals form, not the conditions on the Martian surface [1][3].
• Telling living from non-living signals is hard: Earth's gypsum holds traces of life because microbes are everywhere on Earth. Separating biological from non-biological signals on Mars remains difficult.

Mineralogy therefore works at three levels: it detects past water, describes that water's chemistry, and preserves possible traces of life. A combined approach would make the most of it: orbital mapping, testing instruments at analogue sites, and shared spectral libraries listed on I-STEM. Such an approach would strengthen India's planetary science and advance humanity's oldest question, whether we are alone.