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India’s Chandrayaan-3 spacecraft has begun releasing important data from the scientific experiments being conducted by the instruments on board. On Sunday, the Indian Space Research Organisation (ISRO) released first-of-its-kind data from the observations made by ChaSTE (Chandra’s Surface Thermophysical Experiment), one of the four instruments on the lander module.
ChaSTE is meant to study the heat conductivity of the Moon’s surface and measure the differences in temperatures at different points on and below the surface, with the overall objective of creating a thermal profile of the Moon. This instrument has been developed by the Space Physics Laboratory at the Vikram Sarabhai Space Centre in Thiruvananthapuram and the Physical Research Laboratory in Ahmedabad.
The first set of data released by ISRO showed a very sharp difference in temperatures just above and below the surface of the Moon. A graphical plot put out by ISRO showed that while temperatures on the surface were over 50 degree Celsius, they dropped to nearly -10 degree Celsius just a few millimetres below the surface. The measurements suggested that the topsoil of the lunar surface did not conduct heat very well, and insulated the sub-surface from heat.
The measurements are consistent with what is known about the thermal profile of the Moon from previous expeditions and experiments. But this is the first direct measurement of temperatures of the topsoil and the subsoil near the South Pole of the Moon.
Temperature variation on the Moon is relatively well-known. Even on the surface, there is a huge difference between day-time and night-time temperatures. Some places on the Moon are known to be colder than -200 degree Celsius at night time while others can get hotter than 100 degree Celsius during the day.
Scientists have been studying the temperature variations on the Moon since the start of the lunar missions in the 1960s and 1970s. In addition, samples brought back by the Apollo and other missions have also contributed to this knowledge, as scientists have been able to study their heat-conducting properties.
Using this information, scientists have built three-dimensional models of the thermal environment on the Moon. It is known that a thin upper layer of the lunar surface, a few cm thick, shows very low thermal conductivity. Below that, however, thermal conductivity is high, which means that after a few centimetres of depth, temperature is almost stable and no longer shows a sharp drop. But the picture of the thermal environment is far from complete. The kind of observations being made by ChaSTE not just help in validating these existing models, but also provide entirely new insights with exact quantitative measurements.
Human beings are still learning about the Moon. And the current round of experiments, by the Chandrayaan missions and others, is focussed on creating a full knowledge of what it means to be on the Moon.
The temperature profile, for example, is essential to know not just the kind of experience that human beings, when they eventually land again (the first set is slated for 2025 in NASA’s Artemis-3 mission), should expect, but also for the kind of materials that can be used on the Moon. Such sharp rise and fall of temperatures can result in appreciable thermal expansion or contraction in materials, and affect experimental set-up and other infrastructure. The kind of activities that can be carried out can be significantly affected by the temperature profile.
Similarly, scientists are trying to have a good idea of the elemental composition of the Moon, the relative abundance of different materials and chemicals, the levels of radiation, and seismic activities. The interest in water stems from this same objective. Water is important not just in sustaining longer-term stays of human beings, but also from the point of view of its utility as a fuel. Water can be split into hydrogen and hydroxyl molecules that can serve as fuel to power rockets into deep space, and for other activities on the Moon.
Ultimately, the objective is to have the Moon serve as a permanent station — like the International Space Station — that can have scientific experiments running continuously and can be visited regularly by astronauts. This would be possible only if scientists are able to utilise the resources available on the Moon to build the infrastructure, and harness energy from a locally available source, like hydrogen from water.
