Researchers from IIT‑Kharagpur and the Physical Research Laboratory (PRL), Ahmedabad, report experimental evidence explaining how the Moon’s unusually titanium‑rich basalts — which can contain up to about 18% titanium dioxide (TiO2), far higher than typical Earth lavas — may have formed. The study, by Himela Moitra, Sujoy Ghosh, Tamalkanti Mukherjee, Saibal Gupta and Kuljeet Kaur Marhas, is published in Geochimica et Cosmochimica Acta and has implications for sample‑return missions such as ISRO’s planned Chandrayaan‑4 (targeted for 2028).
The puzzle stems from the Moon’s early history. About 4.3 billion years ago a global magma ocean crystallised from the outside in, leaving a dense, iron‑ and titanium‑rich ilmenite‑bearing cumulate (IBC) layer. Gravity drove that dense layer downward through a lighter, magnesium‑rich mantle in a process called cumulate overturn; as the IBC sank into hotter regions it partially melted. Those titanium‑rich partial melts are widely believed to be the source of high‑Ti lunar basalts, but past laboratory melts did not match surface basalts — they were either too low in magnesium or too dense to erupt.
To probe this, the team used a piston‑cylinder apparatus at IIT‑Kharagpur able to reach pressures of 1–3 gigapascals (equivalent to roughly 700 km depth) and temperatures up to 1,500°C. They ran two experiment types: a layered setup that placed a synthetic IBC above San Carlos olivine (an Earth analogue for the Moon’s Mg‑rich mantle) and mixed‑material runs that simulated chemical interaction during slow descent or ascent. The layered experiments produced melts with 9–19% TiO2 but were low in magnesium oxide; the mixed runs yielded melts high in magnesium but low in titanium.
When the researchers combined these reaction and mixing outcomes in computer simulations, they reproduced the observed magnesium, titanium, silicon and iron contents of high‑Ti lunar basalts, though the model underestimated aluminium oxide and calcium oxide. The team propose a two‑stage model: very titanium‑rich melts formed and became trapped deep inside the Moon, then later mixed with fresher magma rising from below; the combined melt could erupt as the titanium‑rich basalts seen on the surface. This reservoir mechanism also helps explain why high‑Ti volcanic activity persisted over billions of years rather than only in the Moon’s earliest epoch.
Prof. Sujoy Ghosh said, “Regions near the lunar south pole, such as those being evaluated for Chandrayaan‑4, including areas near Shiv Shakti region, have been studied in detail using data from Chandrayaan‑2, NASA’s Lunar Reconnaissance Orbiter, and other missions. What our work adds is a deep interior perspective.” Himela Moitra noted that “high‑resolution microscopic cameras on landers can help identify minerals in lunar rocks, while instruments such as X‑ray fluorescence and X‑ray diffraction can determine their chemical composition before collection,” and co‑author Tamalkanti Mukherjee added that Raman and visible‑near infrared spectroscopy can confirm mineral phases, tools already used on Mars missions.
The study also highlights growing indigenous capability: “Indian laboratories, including those at IIT Kharagpur, PRL Ahmedabad, and other ISRO centres, have made significant progress in recent years,” Prof. Ghosh said, calling the work an important step toward carrying out high‑pressure planetary interior experiments entirely within India. The findings could help prioritise landing sites for future sample‑return missions and guide the in‑situ instruments that will search for and characterise titanium‑bearing lunar rocks.
Original Source: https://www.thehindu.com/sci-tech/science/ahead-of-chandrayaan-4-iit-and-prl-team-decodes-moons-titanium-rich-rocks/article70778152.ece
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Publish Date: 2026-03-24 08:10:00
