Data from Chandrayaan-3's Vikram lander has revealed a remarkably active electrical environment near the Moon’s southern pole, presenting new insights into the plasma that envelops this region.

This discovery emerged from observations collected between August 23 and September 3, 2023, and offers the first direct measurements of near-surface plasma at such low altitudes in the Moon’s southern high latitudes, reported Chetan Kumar of Times News Network.

The Moon’s plasma environment is formed by charged particles, primarily ions and free electrons, which together constitute a plasma—considered the fourth state of matter.

Despite being electrically neutral overall, plasma is highly responsive to electromagnetic forces. The near-surface plasma layer on the Moon is shaped mainly by the solar wind, the photo-electric effect, and the Moon’s intermittent immersion in Earth’s magnetotail.

The solar wind comprises a steady stream of charged particles emanating from the Sun, constantly bombarding the lunar surface. The photo-electric effect involves high-energy solar radiation ejecting electrons from atoms in the lunar Regolith and its extremely thin atmosphere, known as an exosphere, causing ionisation.

When the Moon passes through Earth’s magnetotail for several days each month, charged particles from Earth’s magnetic field further interact with the lunar surface, modulating the plasma environment.

Measurements taken at a site called Shiv Shakti Point (located at 69.3° S, 32.3° E) by the Radio Anatomy of the Moon Bound Hypersensitive ionosphere and Atmosphere – Langmuir Probe (RAMBHA-LP) showed electron densities ranging between 380 and 600 electrons per cubic centimetre. These figures notably exceed previous estimates derived from radio occultation techniques, which observed changes in radio signal phases passing through the Moon’s exosphere from orbit.

In addition to measuring electron densities, the RAMBHA-LP instrument detected high-energy electrons with kinetic temperatures between 3,000 and 8,000 Kelvin. This indicates an electrically dynamic environment constantly influenced by particle flows from both the Sun and Earth. Notably, the data reveal that this plasma behaviour is not static; it fluctuates with the lunar orbit.

During lunar daytime, when the surface is exposed to direct sunlight and lies outside the Earth’s magnetic field influence, electron density variations are predominantly driven by collisions between solar wind particles and the Moon’s exosphere.

Conversely, when the Moon enters the geomagnetic tail—a region shaped by Earth’s magnetic field stretching into space—the plasma environment is significantly impacted by the influx of charged particles from Earth.

Further analysis with an in-house Lunar Ionospheric Model points to molecular ions, likely originating from small amounts of gases such as carbon dioxide and water vapour, contributing to the charged near-surface layer. This suggests a complex interplay between solar, terrestrial, and lunar sources influencing the Moon’s plasma environment.

The information gathered by the RAMBHA-LP will be crucial for future lunar missions, particularly those planned to operate around the polar regions. Understanding plasma activity is essential because it affects vital factors such as communication reliability, surface electrostatic charging, dust transport, and the performance of scientific instruments.

The RAMBHA-LP instrument itself was developed by the Space Physics Laboratory at the Vikram Sarabhai Space Centre in Thiruvananthapuram, part of ISRO.

The findings underscore the value of in-situ measurements on the lunar surface to gain “ground truth” data that enhances our understanding of the Moon’s near-surface space environment, a key factor for the sustainability and success of upcoming exploration endeavours.

Based On TOI Report