Chandrayaan-1 data helps identify possibly oldest lunar impact basin

The brief

Context

Impact basins are giant craters, often hundreds of kilometres wide, formed on the Moon by asteroid or meteorite strikes, and they often preserve traces of ancient volcanism. Scientists believe the Moon has about 300 such basins, but only 74 have been detected so far because older ones have eroded rims that defeat modern imaging. A team at the Physical Research Laboratory (PRL), Ahmedabad, has now confirmed a hidden basin — the Australe Basin — in the Moon's southeastern hemisphere using mineralogical data from India's Chandrayaan-1 mission, in a study published in The Planetary Science Journal. The basin may be older than the South Pole Aitken Basin, so far regarded as the Moon's largest and oldest known basin.

Key facts

• PRL, Ahmedabad scientists confirmed the hidden Australe Basin in the Moon's southeastern hemisphere; the study is published in The Planetary Science Journal.
• The Australe Basin could be older than the South Pole Aitken Basin, the largest and oldest known lunar basin, formed over 4 billion years ago.
• Scientists estimate about 300 impact basins exist on the Moon; only 74 have been detected so far.
• The basin's mineralogy was mapped using NASA's Moon Mineralogy Mapper, an imaging spectrometer operating between 405 and 3000 nanometres.
• Chandrayaan-1 carried 11 scientific payloads, six of them contributed by international agencies including NASA and the European Space Agency.
• Australe basalts are relatively lower in calcium and higher in magnesium, unlike most lunar basalts which are high in calcium, said lead author Neha Panwar.
• The Australe province has 248 small basalt ponds arranged in a circular pattern, unlike the smooth, vast hardened lava surfaces of known basins.
• The Chandrayaan-3 landing site, Shiv Shakti point, shows higher magnesium concentrations and lies about 350 km from material possibly sourced from the South Pole Aitken Basin.

Timeline

1. Over 4 billion years agoSouth Pole Aitken Basin, the largest and oldest known lunar impact basin, was formed; the Australe Basin could be even older.
2. Chandrayaan-1 missionIndia's lunar orbiter carried 11 payloads, including NASA's Moon Mineralogy Mapper, which gathered the mineralogical data later used in the study.
3. Chandrayaan-3 missionLanding site named Shiv Shakti point found to have higher magnesium concentrations.
4. Current study (date not stated in the source)PRL scientists publish confirmation of the Australe Basin in The Planetary Science Journal.
5. Planned/futureNASA's proposed Moon Base mission and India's Chandrayaan-4 lunar sample return mission could use these mineralogical insights.

Who has a stake

• Physical Research Laboratory (PRL), Ahmedabad — Its team identified the Australe Basin, establishing Indian leadership in lunar geology analysis.
• Neha Panwar, planetary scientist and lead author — Reported the unique low-calcium, high-magnesium basalt mineralogy and framed its use for future landing missions.
• ISRO / Chandrayaan programme — Chandrayaan-1 data delivers new science a decade on; Chandrayaan-4 sample return can target such unique sites.
• NASA — Contributed the Moon Mineralogy Mapper to Chandrayaan-1 and plans a Moon Base mission that needs regional mineralogy.
• European Space Agency — Among international agencies that contributed six of Chandrayaan-1's 11 payloads.
• Future South Polar lunar missions — Need to understand how regolith near the South Pole evolved over billions of years, including material excavated by the Australe impact.

Why it matters

A basin possibly older than the South Pole Aitken Basin pushes back the record of the Moon's earliest violent history and adds to the small tally of 74 detected basins out of an estimated 300. Its unusual magnesium-rich, calcium-poor basalts and 248 circular basalt ponds mark it as a distinctive target for sample return. Because the region lies near the lunar South Pole, where India's Chandrayaan-4 and NASA's Moon Base ambitions are focused, the findings help interpret what future landers will actually pick up.