Chandrayaan-2 detects solar ejection's impact on moon's atmosphere

BENGALURU: India’s Chandrayaan-2 lunar orbiter has made a first-of-its-kind observation of how a massive solar eruption affects the Moon’s tenuous atmosphere. The discovery, made by the Chandra’s Atmospheric Composition Explorer-2 (CHACE-2) instrument onboard, provides direct evidence of how the Sun’s coronal mass ejections (CMEs) interact with airless celestial bodies such as the Moon.

A CME is a large burst of plasma and magnetic field released from the Sun’s outer atmosphere, often sending charged particles hurtling through the solar system. When such a CME struck the Moon on May 10, 2024, CHACE-2 detected a sharp rise in the total pressure and the number density — the concentration of atoms and molecules — in the lunar dayside exosphere.

The values increased by more than an order of magnitude compared to normal conditions, marking the first recorded instance of a CME’s direct impact on the Moon’s atmospheric boundary.

The findings, published in the journal Geophysical Research Letters, confirm long-standing theoretical models that predicted such solar events could momentarily alter the lunar exosphere.

Scientists explained that when high-energy solar particles hit the Moon’s surface, they can knock off atoms and molecules, which then form part of the exosphere — a layer so thin that its particles rarely collide.

The Moon’s exosphere is primarily shaped by solar radiation, the solar wind, and micrometeorite impacts. Unlike Earth, the Moon lacks a global magnetic field or a substantial atmosphere to shield it from solar activity. This makes it a natural laboratory to study how solar emissions influence unprotected planetary surfaces.

According to Isro, the observation provides valuable insights into “space weather effects on the Moon,” helping scientists understand how solar activity can temporarily alter its near-surface environment. “Such findings are crucial as they inform both scientific interpretation and engineering design for future lunar missions,” the space agency said.

As multiple countries, including India, plan long-term stays and research stations on the Moon, such data could be vital for mission planning. Engineers and scientists designing lunar habitats and instruments will need to account for the temporary but significant environmental changes triggered by CMEs.

The study, titled “Impact of a Coronal Mass Ejection on the Lunar Exosphere as Observed by CHACE-2 on the Chandrayaan-2 Orbiter”, was authored by MB Dhanya, Chemukula Mathin Yadav, Smitha V Thampi, Tirtha Pratim Das, R Satheesh Thampi, and Anil Bhardwaj from Isro.