Chandrayaan-2 Makes First-Ever Observation of Sun's Impact on Moon: ISRO

In a landmark achievement, India's Chandrayaan-2 mission has made history by directly observing the impact of solar Coronal Mass Ejections (CMEs) on the Moon's exosphere. The Indian Space Research Organisation (ISRO) announced that this is the first time such an event has been directly observed, providing valuable insights into the lunar environment and space weather.

Launched on July 22, 2019, Chandrayaan-2 has been orbiting the Moon, carrying eight scientific payloads to study the lunar surface, geology, and exosphere. On May 10, 2024, a series of CMEs were emitted from the Sun, offering a rare opportunity to observe their effects on the Moon.

The Chandra's Atmospheric Composition Explorer-2 (CHACE-2) instrument onboard Chandrayaan-2 recorded a significant increase in the total pressure of the Moon's dayside exosphere when the CMEs impacted. The lunar exosphere is an extremely thin atmosphere where gas atoms and molecules rarely interact. The total number density, which measures the concentration of neutral atoms or molecules, increased by more than an order of magnitude. This observation validates earlier theoretical models that predicted such an effect, but this is the first time it has been directly observed.

CMEs occur when the Sun ejects significant amounts of plasma, primarily composed of hydrogen and helium ions, into space. The Moon, lacking a substantial atmosphere and a global magnetic field, is particularly vulnerable to solar activity. When a CME strikes the Moon, the increased solar material enhances surface sputtering, a process where solar ions knock atoms off the surface. This leads to a temporary increase in the density and pressure of the exosphere.

ISRO scientists noted that the May 2024 CME event provided a unique opportunity to closely examine these interactions. The enhanced presence of liberated atoms following the CME matched well with prior model predictions, validating earlier simulations of lunar space weather dynamics. The study, titled "Impact of a Coronal Mass Ejection on the Lunar Exosphere as Observed by CHACE-2 on the Chandrayaan-2 Orbiter," was published in Geophysical Research Letters on August 16, 2025.

This breakthrough has significant implications for future lunar exploration. Understanding how the Moon responds to solar disturbances is crucial for long-duration missions and establishing surface habitats. Space weather events like CMEs can temporarily alter the lunar environment, posing challenges for equipment operation and human activity on the surface. Lunar base architects will need to consider these extreme events and their potential impact on the lunar environment.

Chandrayaan-2, despite the Vikram lander's unsuccessful landing in 2019, continues to provide valuable data and enhance our understanding of the Moon. This first-ever observation of the Sun's impact on the Moon's exosphere marks a significant milestone in lunar science and highlights the importance of continued lunar exploration.