The electrical environment near the Moon’s surface in the south polar region is far more active than previously understood, ISRO said on Tuesday, based on an analysis of Chandrayaan-3 lander data.
The Chandrayaan-3 data, obtained between August 23 and September 3, 2023, provided critical ground truth on the Moon’s plasma environment. In a statement, ISRO said, “Analysis of the Chandrayaan-3 lander data has yielded significant and first-of-its-kind results on the plasma environment near the Moon’s surface at southern higher latitudes, revealing that the electrical environment near the Moon’s surface in the south polar region is far more active than previously understood.”
In physics, plasma is often called the fourth state of matter, consisting of a mixture of charged particles, including ions and free electrons. Despite being electrically neutral overall, plasma is highly conductive and responds strongly to electromagnetic fields.
“The Moon’s thin plasma environment, or lunar ionosphere, is governed by several major processes. Solar wind, a continuous stream of charged particles (primarily electrons and hydrogen and helium ions) ejected from the Sun’s upper atmosphere, constantly impinges on the Moon’s surface,” ISRO said.
This, along with the photoelectric effect, where high-energy photons from the Sun knock out outer-shell electrons from atoms on the surface and in the sparse atmosphere, causing ionisation, is the primary mechanism for generating plasma.
The lunar plasma is further influenced by the deposition of charged particles originating from the Earth’s magnetosphere (specifically the magnetotail) when the Moon passes through that region, typically for 3 to 5 days during 28 days, resulting in a constantly changing and dynamic electrical environment near the surface, ISRO said.
The results, obtained by the Radio Anatomy of the Moon Bound Hypersensitive Ionosphere and Atmosphere Langmuir Probe (RAMBHA-LP) instrument onboard the Vikram lander of Chandrayaan-3, mark the first-ever direct, or “in situ”, measurements of lunar plasma at such low altitudes, it added.
The agency said the electron density near the Chandrayaan-3 landing site, named Shiv Shakti Point, was measured to be between 380 and 600 electrons per cubic centimetre.
“This is significantly higher than estimates derived from observations taken at higher altitudes, which are primarily based on changes in the phase of electromagnetic signals from satellites passing through the Moon’s thin atmosphere at grazing angles, a technique known as radio occultation,” ISRO said.
It also found that electrons near the Moon’s surface possess remarkably high energy, with equivalent (kinetic) temperatures ranging from 3,000 to 8,000 Kelvin.
“The study uncovered that the lunar plasma is not static but is constantly modulated by two distinct factors, depending on the Moon’s orbital position around the Earth,” it noted. “These results from the RAMBHA-LP experiment provide essential ground truth needed for the next phase of lunar exploration,” ISRO added. The RAMBHA-LP experiment was designed and developed by the Space Physics Laboratory (SPL) at the Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram.
