The Radio Anatomy of Moon Bound Hypersensitive ionosphere and Atmosphere - Langmuir Probe (RAMBHA-LP) payload on board Chandrayaan-3’s lander Vikram has completed the first in-situ measurements of the surface-bound lunar plasma environment over the south polar region.
The RAMBHA-Langmuir Probe (RAMBHA-LP), named after American chemist and physicist Irving Langmuir, who was awarded the Nobel Prize in Chemistry, is a device used for characterising a plasma.
“The initial assessment indicates that the plasma encompassing the lunar surface is relatively sparse, characterised by a number density ranging from approximately 5 to 30 million electrons per cubic meter. This evaluation specifically pertains to the early stages of the lunar daytime. The probe operates without interruption, aiming to explore the changes occurring in the near-surface plasma environment throughout the lunar day. These ongoing observations hold significant implications for comprehending the process of charging within the lunar near-surface region, particularly in response to the fluctuations in solar space weather conditions,” ISRO said on Thursday.
According to the space agency, the device features a 5 cm metallic spherical probe mounted on a 1-metre boom attached to the Chandrayaan-3 lander’s upper deck.
“The probe is deployed using a hold-release mechanism after the lander’s lunar touchdown. The extended boom length ensures that the spherical probe operates within the undisturbed lunar plasma environment, isolated from the lander’s body. The system can detect minute return currents, as low as pico-amperes, with a dwell time of 1 millisecond. By applying a sweeping bias potential ranging from -12 to +12 V in increments of 0.1 V to the Langmuir probe, the system can accurately determine ion and electron densities as well as their energies based on the measured return current,” ISRO added.
Development of RAMBHA-LP was led by Space Physics Laboratory (SPL), Vikram Sarabhai Space Centre (VSSC), Thiruvananthapuram.
Relatively sparse
“The initial assessment indicates that the plasma near the lunar surface is relatively sparse. These quantitative measurements potentially assist in mitigating the noise that lunar plasma introduces into radio wave communication. Also, they could contribute to the enhanced designs for upcoming lunar visitors,” ISRO posted on X (formerly Twitter).
Continuing with the scientific experiments, Instrument for Lunar Seismic Activity (ILSA) payload has recorded the vibrations occurring due to the movements of rover and other payloads.
Additionally, it has recorded an event, appearing to be a natural one, on August 26, 2023. The source of this event is under investigation, ISRO said.
Earlier in the day, ISRO said that another instrument on board the Chandrayaan-3 rover Pragyan has confirmed the presence of Sulphur (S) in the south polar region. On August 28, the Laser-Induced Breakdown Spectroscopy (LIBS) instrument aboard Pragyan confirmed the presence of sulphur in the region unambiguously. Now the Alpha Particle X-ray Spectroscope (APXS) instrument has also confirmed the presence of sulphur.
“Another instrument on board the rover confirms the presence of sulphur (S) in the region, through another technique. The Alpha Particle X-ray Spectroscope (APXS) has detected S, as well as other minor elements. This finding by Ch-3 compels scientists to develop fresh explanations for the source of sulphur (S) in the area: intrinsic?, volcanic?, meteoritic?,......?.” ISRO posted on X.
ISRO said the APXS instrument was best suited for in-situ analysis of the elemental composition of soil and rocks on the surface of planetary bodies having little atmosphere, such as the moon.
It carries radioactive sources that emit alpha particles and X-rays onto the surface sample. The atoms present in the sample in turn emit characteristic X-ray lines corresponding to the elements present. By measuring the energies and intensities of these characteristic X-rays, researchers can find the elements present and their abundances.
“APXS observations have discovered the presence of interesting minor elements, including sulphur, apart from the major expected elements such as aluminium, silicon, calcium and iron. It may be recalled that the LIBS instrument on board the rover also confirmed the presence of sulphur. Detailed scientific analysis of these observations are in progress,” the space agency said.
APXS is developed by the Physical Research Laboratory (PRL), Ahmedabad, with support from the Space Application Centre (SAC) Ahmedabad, whereas the U.R. Rao Satellite Centre (URSC), Bengaluru, built the deployment mechanism.
ISRO said that Pragyan, with its scientific instruments, is trying to find answers to questions like “What are lunar soil and rocks made of in the south polar region and how’s it different from other highland regions?”
ISRO also released a video showing an automated hinge mechanism rotating the 18 cm tall APXS, aligning the detector head to be approximately 5 cm in proximity to the lunar surface. The video is captured by the lander camera.
The space agency also shared a video of the rover rotating in search of a safe route which was captured by a lander imager camera.
