India’s Chandrayaan-3 lander made a historic touchdown 600 km from the south pole of the moon on August 23, 2023, marking an exciting milestone for lunar scientists worldwide. In less than 14 Earth days, Chandrayaan-3 has already provided scientists with valuable new data, offering further inspiration to explore the moon. The Indian Space Research Organisation (ISRO) has generously shared these initial findings with the world.
One of the unexpected surprises from Chandrayaan-3’s rover, Pragyan (meaning “wisdom” in Sanskrit), is the discovery of sulphur in the lunar soil. Planetary scientists have long known that sulphur exists in lunar rocks and soils, but only in very low concentrations. However, the recent measurements suggest a higher sulphur concentration than previously anticipated. This new revelation has sparked great interest among scientists.
Pragyan is equipped with two instruments for analyzing the elemental composition of the soil – an alpha particle X-ray spectrometer and a laser-induced breakdown spectrometer (LIBS). Both of these instruments have detected sulphur in the soil near the landing site. This finding is significant because sulphur in the soils near the moon’s poles could potentially be a valuable resource for future astronauts, enabling them to sustain themselves on the moon.
To understand the importance of this discovery, it’s essential to explore the geology of the moon. The lunar surface is predominantly composed of two rock types – dark volcanic rock and brighter highland rock. The contrast in brightness between these materials creates recognizable patterns on the moon’s surface when observed with the naked eye, such as the “man in the moon” face or the image of a “rabbit picking rice.”
Scientists studying lunar rock and soil compositions in labs on Earth have observed that materials from the dark volcanic plains tend to have higher sulphur content compared to the brighter highlands material. This correlation suggests that sulphur primarily originates from volcanic activity. Rocks deep within the moon’s crust contain sulphur, and when these rocks undergo melting, the sulphur becomes part of the magma. As the magma rises closer to the lunar surface, most of the sulphur, alongside water vapor and carbon dioxide, is released into the atmosphere as gas.
However, some of the sulphur remains within the magma and gets retained within the rock after it cools down. This process explains the association of sulphur with the moon’s dark volcanic rocks. The presence of sulphur in the soils near the moon’s poles indicates unique environmental conditions in these regions. Due to less direct sunlight, the poles experience significantly lower temperatures than the rest of the moon. If the surface temperature falls below -73 degrees Celsius, sulphur from the lunar atmosphere can condense and solidify on the surface, resembling frost on a window. Additionally, sulphur at the poles might have originated from ancient volcanic eruptions or meteorites containing sulphur that vaporized upon impact with the moon’s surface.
The measurement of sulphur is intriguing to scientists for two primary reasons. Firstly, it suggests that the highland soils at the lunar poles have fundamentally different compositions compared to highland soils at the equatorial regions. This compositional difference arises due to variations in environmental conditions between the two regions, with the poles receiving less direct sunlight. Secondly, the presence of concentrated sulphur at the polar regions raises questions about its formation. It is hypothesized that the sulphur could have formed from the extremely thin lunar atmosphere or could be remnants of ancient volcanic eruptions or meteorite impacts.
Looking towards the future, sulphur in lunar soils could serve as a valuable resource for long-lasting space missions. Many space agencies have contemplated building bases on the moon, where astronauts and robots could utilize naturally occurring resources like sulphur through a concept known as in-situ resource utilization. This approach minimizes the need for multiple trips back to Earth for supplies and maximizes exploration time and energy. With sulphur, astronauts could potentially construct solar cells, batteries, fertilizers, and even concrete for construction purposes on the moon. Sulphur-based concrete offers several advantages over conventional concrete, including faster hardening times and increased resistance to wear. Moreover, it does not require water in the mixture, enabling astronauts to conserve their limited water supply for essential needs like drinking, producing breathable oxygen, and creating rocket fuel.
While there are currently seven missions operating on or around the moon, the lunar south pole region has not been studied extensively from the surface until now. The new measurements collected by Pragyan will greatly enhance our understanding of the moon’s geological history. These findings will also stimulate new research questions about the moon’s formation and evolution.
The data collected by Chandrayaan-3 is currently being processed and calibrated by the scientists at ISRO. As the lunar night approaches, with temperatures dropping to a bone-chilling -120 degrees Celsius, Chandrayaan-3 will enter hibernation mode to withstand the harsh conditions. The night will last until September 22. While there is uncertainty regarding the survival of the lander component, called Vikram, or the rover, Pragyan, in such extreme temperatures, their potential reactivation holds the promise of gathering more valuable measurements.
In conclusion, India’s Chandrayaan-3 mission to the moon has already provided unprecedented insights and inspiration for further lunar exploration. The discovery of sulphur in the lunar soils, specifically near the moon’s poles, opens up exciting possibilities for future manned missions and utilization of in-situ resources. As scientists eagerly await fully calibrated data to confirm the elevated sulphur concentration, the findings from Chandrayaan-3 help unravel the mysteries of the moon’s geology and fuel our curiosity about its formation and evolution.
Jeffrey Gillis-Davis is a research professor of physics at Washington University in St. Louis. (source: The Conversation)