Model Answer

Introduction

The lunar exosphere is an extremely tenuous, surface-bounded “atmosphere” where neutral atoms/molecules exist at very low densities. CHACE-2 (Chandra's Atmospheric Composition Explorer-2) is a mass-spectrometer-type payload onboard the Chandrayaan-2 orbiter designed to measure the composition, number density and temporal variations of these neutral species. On 10 May 2024, a series of Coronal Mass Ejections (CMEs) from the Sun impacted the Moon. CHACE-2 recorded a pronounced response: the dayside lunar exospheric total pressure rose and the total number density of neutral atoms increased by more than an order of magnitude. The data indicate an enhanced release of surface atoms into the exosphere concurrent with the CME impact.

Body

1. Unique Observation:

   • In May 2024, the CHACE-2 instrument made a path-breaking discovery when a Coronal Mass Ejection (CME) from the Sun directly impacted the Moon. This was the first-ever recorded observation of CME effects on the lunar exosphere.
   • The data showed a significant increase in total pressure and particle density on the Moon's dayside.
   • The number density of neutral atoms increased by more than an order of magnitude, confirming that energetic solar particles can knock atoms off the lunar surface.

2. Mechanism Behind the Observation:

   • CMEs are massive bursts of charged plasma from the Sun's corona that carry intense magnetic fields. When such a burst interacts with the lunar surface — which lacks a protective magnetic field or thick atmosphere — it leads to:
     1. Sputtering: Solar energetic particles physically eject atoms from the lunar regolith.
     2. Surface charging: The interaction alters the electrostatic environment, enhancing particle mobility.
     3. Thermal desorption: High-energy radiation heats the surface, releasing trapped gases.
   • These combined processes enrich the exosphere temporarily, proving theoretical models about space weather-surface interaction.

3. Contribution to Scientific Understanding:

   • CHACE-2's measurements have deepened scientific insights in several ways:
     1. It provided empirical evidence of how solar events alter the Moon's near-surface environment.
     2. The data helps in validating and improving lunar exosphere models, especially regarding variability during solar storms.
     3. It enhances understanding of space weather dynamics — a crucial field in planetary science and future space missions.

4. Practical Implications for Lunar Exploration:

   • The findings are not only academic but also have engineering and operational importance:
     1. Lunar base design: Engineers must consider the temporary atmospheric and electrostatic changes during CMEs.
     2. Equipment durability: Increased radiation and particle density can affect sensors and communication devices.
     3. Human safety: Understanding such events aids in planning safe time windows for lunar surface activities.

Conclusion/Way Forward

Through CHACE-2, Chandrayaan-2 has provided the first concrete evidence of how solar activity influences the Moon's exosphere. This discovery bridges the gap between space weather physics and lunar science, while also guiding the design of sustainable human presence on the Moon. It showcases ISRO's growing capability in not just exploration but in fundamental planetary research as well.