Chandrayaan-3 detects surprisingly active plasma over Moon’s south pole

Key facts

• Chandrayaan-3 detects surprisingly active plasma over the Moon’s south pole.
• The Radio Anatomy of the Moon Bound Hypersensitive ionosphere and Atmosphere–Langmuir Probe (RAMBHA-LP) instrument offers the first ground truth of the Moon’s near-surface plasma at southern high latitudes.
• The lander Vikram’s data showed that electrons close to the ground carry surprisingly high energies.
• Their kinetic temperatures were measured at roughly 3,000 to 8,000 Kelvin, indicating a plasma layer far more energised than previously understood.
• Just above the surface, the “plasma” (a mix of charged particles) is far denser and more energetic than earlier remote observations.
• Plasma is often described as the fourth state of matter, a blend of charged particles such as ions and free electrons.
• On the Moon, this thin plasma layer, sometimes called the lunar ionosphere, is shaped by a complex mix of processes.
• A constant flux of solar wind streams of electrons and ions rushed out from the Sun and strikes the Moon’s airless surface.
• Through the photoelectric effect, high-energy sunlight also removes electrons from surface atoms, increasing the ionised environment.
• The Moon receives a new supply of charged particles from our planet’s extended magnetic field as it drifts into Earth’s magnetotail for a few days.
• At the mission’s landing site Shiv Shakti Point (69.3° S, 32.3° E), the RAMBHA-LP instrument detected electron densities ranging between 380 and 600 particles per cubic centimetre.
• These values are markedly higher than earlier estimates, which relied on remote-sensing techniques such as radio occultation.
• Researchers found that this plasma does not remain steady but changes depending on the Moon’s position during its orbit around Earth.
• During lunar daylight, when the Moon is fully exposed to the Sun, and outside Earth’s magnetic influence, the interaction between solar wind particles and the Moon’s sparse exosphere drives much of the variation.
• When the Moon enters the geomagnetic tail on the far side of Earth, the plasma takes on a different character, shaped by streams of charged particles flowing through that elongated magnetic region.
• Insights from the mission also suggest that molecules such as carbon dioxide and water vapour may contribute to the behaviour of the lunar ionosphere.
• According to the Lunar Ionospheric Model developed in-house, molecular ions alongside the expected elemental ones play a meaningful role in forming the charged layer hovering near the surface.
• These measurements provide essential “ground truth” for future lunar exploration, especially for missions targeting the Moon’s southern high latitudes.
• RAMBHA-LP’s development was spearheaded by the Space Physics Laboratory at the Vikram Sarabhai Space Centre in Thiruvananthapuram.