In a remarkable scientific breakthrough, researchers from the Space Physics Laboratory (SPL) at the Vikram Sarabhai Space Centre (VSSC) have unveiled surprising insights into the Moon’s ionosphere.
By analyzing radio signals from India’s Chandrayaan-2 orbiter, which continues to operate efficiently and provide valuable data, researchers have discovered an unexpectedly high electron density in the lunar environment, particularly when the Moon enters the Earth’s geomagnetic tail.
This finding challenges long-held assumptions about plasma behavior around the Moon and suggests a more prominent role for the Moon’s remnant magnetic fields than previously thought.
The SPL team employed a cutting-edge technique using S-band Telemetry and Telecommand (TTC) radio signals. In a two-way radio occultation experiment, they tracked Chandrayaan-2’s transmissions through the Moon’s plasma layer, with signals received at the Indian Deep Space Network (IDSN) in Byalalu, Bangalore.
The results were groundbreaking. They revealed electron densities of approximately 23,000 electrons per cubic centimeter—nearly 100 times higher than those on the Moon’s sunlit side.
Interestingly, these densities are comparable to the levels observed in the Moon’s wake region, previously discovered by the same team.
The Moon passes through Earth’s extended magnetic field—known as the geotail—for about four days during each orbit. It was previously thought that plasma levels would drop during this time because the Moon is shielded from solar wind, allowing the plasma to spread out along Earth’s magnetic field. However, Chandrayaan-2’s findings have proven this assumption wrong.
Researchers propose that the Moon’s crustal magnetic fields may act as plasma traps, preventing diffusion and resulting in localized electron density enhancements. To verify their hypothesis, they used the in-house Three-Dimensional Lunar Ionospheric Model (3D-LIM), which simulated plasma dynamics under varying conditions.
The model confirmed that such high plasma densities are only sustainable in the geotail when the ionosphere achieves photochemical equilibrium—a state dependent on the presence of crustal magnetic fields.
Earth’s magnetic field changes 10 times faster than previously thought
Additionally, the simulations identified reduced neutral Argon (Ar) and Neon (Ne) densities near the Moon’s poles, consistent with earlier spacecraft observations.
Discovering high plasma densities is significant because it can affect radio signals, cause surface charging, and interact with lunar dust—all vital considerations for upcoming lunar missions.
Gaining insights into how the lunar ionosphere behaves in different conditions will also help design better habitats and infrastructure, especially in areas influenced by the Moon’s magnetic fields.
This study highlights Chandrayaan-2’s remarkable contribution to lunar research, showcasing its importance in revealing the mysteries of the Moon’s plasma environment.
Journal Reference
- Keshav R. Tripathi, R. K. Choudhary, and K. M. Ambili. Lunar Ionosphere in the Geotail Region as Observed by Chandrayaan-2 Orbiter Using Two-way Radio Occultation Measurements. The Astrophysical Journal – Letters. DOI: 10.3847/2041-8213/adb3a7
