Significant Discovery: Chandrayaan-1 Found Water on the Moon
September 2009 — the finding that changed lunar science.
On 24 September 2009, scientists announced that data from Chandrayaan-1's instruments provided clear evidence of water on the Moon. Two independent lines of evidence converged.
Moon Impact Probe (MIP)
The MIP's CHACE mass spectrometer, during its 25-minute descent to the lunar south pole on 14 November 2008, directly detected water vapour in the extremely thin lunar atmosphere. ISRO announced this result after NASA's findings were published, noting that its own data had shown the water signature months earlier.
Moon Mineralogy Mapper (M3)
NASA's M3 imaging spectrometer aboard Chandrayaan-1 detected absorption features near 2.8–3.0 µm across the lunar surface — the spectral fingerprint of hydroxyl (OH) and water (H2O) molecules. The signal was strongest at higher latitudes. The findings were published in the journal Science and corroborated by NASA's Cassini and Deep Impact/EPOXI spacecraft data.
Why it matters
The discovery overturned decades of assumption that the Moon was bone dry. It made the lunar poles — where later radar and neutron data indicated substantial water-ice deposits — the prime target for future exploration, including Chandrayaan-3's historic 2023 south pole landing and the upcoming ISRO–JAXA Chandrayaan-5/LUPEX water-ice mission. In 2018, re-analysis of M3 data definitively confirmed exposed water ice in permanently shadowed polar regions.
Sources: Wikipedia — Chandrayaan-1; NASA/ISRO announcements, September 2009