Chandrayaan-3: Sulphur On Moon's South Pole, Lunar Quake — Vikram And Pragyan's Findings So Far

Chandrayaan-3's Vikram lander and Pragyan rover have made groundbreaking scientific discoveries and performed breakthrough experiments in just a week of starting operations on the Moon.

Chandrayaan-3's Vikram lander and Pragyan rover have made groundbreaking scientific discoveries and performed breakthrough experiments in just a week of starting operations on the Moon. Both Vikram and Pragyan started operations on August 24, 2023, the day after Chandrayaan-3 successfully soft landed on the Moon's south pole, making India the first country to softly land a spacecraft on the lunar south pole. 

The Vikram lander is equipped with four payloads: Chandra's Surface Thermophysical Experiment (ChaSTE), Instrument for Lunar Seismic Activity (ILSA), Radio Anatomy of Moon Bound Hypersensitive ionosphere and Atmosphere-Langmuir Probe (RAMBHA-LP), and Laser Retroreflector Array (LRA). The LRA, developed by NASA, is the only Instrument onboard Chandrayaan-3 that is not indigenously developed. 

ChaSTE, ILSA, and RAMBHA-LP have already made interesting discoveries on the Moon's south pole. 

The two payloads onboard Pragyan are: Alpha Particle X-ray Spectrometer (APXS) and Laser Induced Breakdown Spectroscope (LIBS). Both APXS and LIBS have discovered the presence of sulphur on the Moon. 

From creating the first temperature-depth profile on the Moon's south pole, to confirming the presence of sulphur on the lunar south pole, from discovering that the lunar plasma environment above the south pole is sparse, to detecting a potential lunar quake, the payloads onboard Vikram and Pragyan achieved several milestones in less than a week. 

Here is the complete list of scientific discoveries made on the Moon by Chandrayaan-3's payloads. 

ChaSTE: First temperature-depth profile of Moon's south pole

On August 27, the Indian Space Research Organisation (ISRO) shared on X (formerly Twitter) that Vikram's ChaSTE payload has generated the first temperature-depth profile of the lunar surface on the Moon's south pole. In order to understand the thermal behaviour of the Moon's surface, ChaSTE measured the temperature profile of the lunar topsoil around the south pole. ChaSTE's temperature probe, which is capable of penetrating to a depth of 10 centimetres into the lunar surface, and is equipped with 10 individual temperature sensors, made measurements which generated the first temperature-depth profile of the lunar soil on the Moon's south pole. The penetration mechanism of the temperature probe can be controlled. The probe recorded the variation of temperature with changing depth in the lunar surface and near-surface lunar regions. 

ChaSTE's aim is to measure thermal properties, including temperature and thermal conductivity, of the lunar surface near the south pole, and understanding how the lunar surface responds to temperature variations will help in understanding the processes that shaped the Moon's terrain over millions of years. 

LIBS and APXS: Sulphur confirmed on Moon's south pole

Pragyan's LIBS payload has confirmed the presence of sulphur in the lunar surface region near the Moon's south pole. The instrument performed the first-ever in-situ measurements on the Moon's south pole, ISRO said on August 29. LIBS has unambiguously confirmed the presence of sulphur on the Moon's south pole. According to ISRO, instruments onboard orbiters sent to the Moon in the past could not have conducted these measurements. 

Apart from sulphur, LIBS also detected elements such as aluminium, calcium, iron, chromium, titanium, manganese, silicon, and oxygen on the lunar south pole. The presence of these elements on the Moon's south pole was expected. 

Now, LIBS is conducting experiments to detect the presence of hydrogen. 

LIBS irradiates lunar materials with intense laser pulses to analyse their composition. Lunar materials include rocks and lunar soil. When LIBS focuses a high-energy laser pulse onto lunar materials, an extremely hot and localised plasma is generated. Plasma refers to a mixture of ionised particles.

Detectors such as charge coupled devices onboard LIBS detect the plasma, and spectrally resolve it. This means that the detectors define the wavelength intervals of the plasma radiation emitted by the material. 

When an element is in its ionised state, it emits a characteristic set of wavelengths of light, and analysing this set of wavelengths helps determine the elemental composition of the material. 

ISRO also released a graph which shows the wavelengths of the plasma light emitted by a certain material on the lunar surface against arbitrary units. The Y-axis represents the relative intensity of the light emitted by a lunar material. The regions in the graph where there is a large peak indicate a greater amount of a certain element, and the areas where there is a smaller peak indicate a smaller amount of the element. 

By analysing the wavelengths, one can determine the elements emitting the plasma light. When an element is irradiated with a laser pulse, it emits a characteristic spectrum of wavelengths. 

APXS is the second Pragyan rover payload which has confirmed the presence of sulphur on the Moon's south pole. However, it used a technique different from that used by LIBS. 

APXS also detected elements such as aluminium, silicon, calcium, and iron. By analysing the lunar soil and rocks on the Moon's south pole, APXS will provide insights into how this region is different from other highland areas. 

APXS is equipped with radioactive materials which emit alpha particles and X-rays onto the lunar surface sample. As a result, different elements present in the sample emit X-ray lines of different wavelengths. APXS measures the energies and intensities of these X-rays in order to determine the kinds of elements present, and also their quantities. 

RAMBHA-LP: Sparse lunar plasma environment

RAMBHA-LP conducted experiments on the Moon's south pole which revealed that the plasma environment above the lunar south pole is sparse. There are about five to 30 million electrons per cubic metre in the lunar plasma. The significance of these findings is that the measurements will allow scientists to understand fluctuations in space weather conditions.

Since the plasma above the lunar near-surface region is subject to charging and ionisation due to fluctuations in solar space weather conditions, measurements by the probe will help scientists obtain more insights into the mechanism of charging in the lunar near-surface region.

ILSA: Vibrations of Pragyan and potential lunar quake

ILSA, which is a first-of-its-kind instrument on the Moon, has recorded the movements of the Pragyan rover, and also the vibrations of an event which appears to be a natural one, potentially a lunar quake. 

ISRO is still investigating the source of the event. 

ILSA's accelerometers allow it to measure the accelerations of objects. When external vibrations occur, the spring inside ILSA is deflected. This leads to a change in capacitance, or the amount of electric charge stored. The change in capacitance is converted into voltage. 

According to K Siddhartha, Earth Scientist at ISRO, the function of ILSA is to detect and study lunar quakes, which are rumblings under the surface of the Moon, and if these rumblings are confirmed, exciting possibilities for future exploration will be opened up. 

Vikram and Pragyan's mission life is expected to end on September 7 or 8.

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