The surface of the Moon is covered in ancient lava flows that are often different from those on Earth. While volcanic rocks on Earth rarely contain more than 2% titanium dioxide (TiO2), some lunar basalts—common volcanic rocks—contain as much as 18%, a fact that planetary scientists have struggled to explain for decades.
A new study by scientists at IIT-Kharagpur and the Physical Research Laboratory (PRL), Ahmedabad, published in Geochimica et Cosmochimica Actanow offered an experimental account of how these titanium-rich basalts could have formed.
The authors of the study were Himela Moitra, Sujoy Ghosh, Tamalkanti Mukherjee, Saibal Gupta and Kuljeet Kaur Marhas.
Cameras on landers
The Chandrayaan-4 mission, planned by the Indian Space Research Organization (ISRO) for 2028, aims to collect rock samples from the Moon and return them to Earth, so choosing a landing site is critical. The results of the study could contribute to this decision.
Prof. Ghosh, one of the lead authors and associate professor at IIT-Kharagpur, said: “Regions near the lunar south pole, such as those assessed on Chandrayaan-4, including those near the Shiv Shakti region, have been studied in detail using data from Chandrayaan-2, NASA’s Lunar Reconnaissance Orbiter and other missions.”
According to the study’s first author, Himel Moitra: “High-resolution microscopic cameras on the landers can help identify minerals in lunar rocks, while tools such as X-ray fluorescence and X-ray diffraction can determine their chemical composition before collection.
“Spectroscopic tools such as Raman and visible-near-infrared spectroscopy can help confirm mineral phases in rocks before they are collected. Similar tools have already been used successfully in missions to Mars,” added Tamalkanti Mukherjee, PhD student at IIT Kharagpur and co-author of the study.
The European Space Agency also plans to launch its Lunar Volatile and Mineralogy Mapping Orbiter mission in 2028 to map the distribution of water and ilmenite on the Moon.
Too high or too low
About 4.3 billion years ago, the Moon was still cooling from a global ocean of molten rock. In this process, olivine and orthopyroxene crystallized first, then plagioclase, which floated up to form the pale lunar crust. A thick layer rich in iron and titanium containing minerals called clinopyroxene, ilmenite and fayalytic olivine was the last to crystallize. Scientists call this the ilmenite cumulative layer (IBC).
The IBC layer was too thick to stay in place. Gravity pulled it down through the less dense, magnesium-rich mantle in a process called accretionary overturning. As it plunged into the warmer regions of the lunar interior, the IBC layer began to melt. The titanium-rich partial melts it produced are widely believed to be the source of the moon’s titanium-rich basalts—but the exact mechanism remained disputed.
When scientists previously tried to melt IBC rocks in the lab, the resulting liquids didn’t match the basalts on the moon’s surface: either they didn’t have enough magnesium or they were too dense to rise and erupt as lava. The authors of the new study set out to find the missing link.
They used a piston cylinder at IIT Kharagpur, which is capable of developing a pressure of up to 3 gigapascals (GPa) of pressure – equivalent to the pressure below 700 km deep inside the moon – and a temperature of 1,500 °C.
The team designed two sets of experiments. In one set, they placed a thin layer of synthetic IBC layer over a layer of San Carlos olivine, a mineral on Earth that is a good proxy for the moon’s magnesium-rich mantle, inside the capsule and exposed it to pressures of 1-3 GPa and temperatures of 1075-1500°C. This setup mimicked where the descending IBC layer makes contact with the casing. In another kind of experiment, the team mixed the two materials together before exposing them to similar conditions, simulating chemical interaction during a slow descent or ascent.
‘significant progress’
The test results indicated that the titanium-rich basalts were formed by a complex process involving both reactions and mixing.
The first kind of experiments generated melts containing 9–19% titanium dioxide, but were stubbornly low on magnesium oxide, the same discrepancy encountered in older studies. Mixed experiments produced basalts that were, on the other hand, too high in magnesium and too low in titanium.
“Indian laboratories, including those at IIT Kharagpur, PRL Ahmedabad and other ISRO centres, have made significant progress in recent years,” said Prof. Ghosh. “Our study shows that high-pressure experimental work related to planetary interiors can now be done exclusively in India, an important step towards building indigenous capabilities in planetary science.”
When the team simulated a combination of these processes and results on a computer, they found that some of the molten rock could have directly risen and exploded with a modest amount of titanium. However, these very titanium-rich rocks could have become stuck deep inside the Moon. Later, fresh magma rising from below could have mixed with these trapped pockets and the associated molten mass could have erupted as titanium-rich lava.
Melt storage
According to the study, this two-stage model could successfully reproduce the observed magnesium, titanium, silicon and iron contents of lunar basalts with high titanium content, but underestimated alumina and calcium oxide.
The model could also explain why high-titanium volcanic activity has continued throughout the moon’s geological history, rather than being limited to its earliest periods: because the natural satellite has had a storehouse of titanium-rich melts in its interior for billions of years, waiting for the right conditions to bring it to the surface.
mukunth.v@thehindu.co.in
Published – 24 March 2026 08:10 IST
