PRL Scientists Develop A Comprehensive 3D Thermophysical Model For The Moon, Useful For Future Lunar Missions Like Chandrayaan-3

Scientists at Ahmedabad-based Physical Research Laboratory (PRL) have created a comprehensive three-dimensional thermophysical model of the Moon.

Their objective with building the model was to derive lunar surface and subsurface temperatures so as to be able to predict a realistic thermal behaviour of the Moon.

This knowledge can help scientists understand Earth’s natural satellite better as well as plan future missions to the Moon, both robotic and crewed.

The research article, authored by K Durga Prasad, Vinai K Rai, and S V S Murty, was published in the journal Earth and Space Science.

The Study

The model visualises the surface of the Moon to have two or more layers — a thin upper layer (few centimetres) of very low thermal conductivity and beneath it a denser layer (approximately 1 metre) of relatively high thermal conductivity.

Scientists can tweak the thickness and other parameters of these lunar layers in the model to arrive at simulations of the most realistic scenario.

The diurnal evolution of surface and subsurface temperatures were calculated using the model. Results showed that the lunar surface structure, including the thickness of the uppermost, porous layer, is an important parameter controlling surface and subsurface temperatures.

The results were validated using laboratory experiments and available data.

“A comparison of the experimental results and model-derived results show a good agreement within the experimental/model uncertainties, validating the credibility of the model for carrying out such complex simulations,” the paper says.

To verify against a “ground truth,” the model results were also verified against Apollo in-situ measurements. Temperature data over one lunar day obtained from the Apollo 15 and 17 heat flow probes was used as the standard.

The results were found to be “in good agreement with both Apollo 15 (∼6 cm above the surface considered as surface value) and Apollo 17 measurements, and surface temperature data derived for the same sites from earlier models.” (Explanation for an observed discrepancy is provided in the paper.)

Many lunar thermophysical models have been developed since the 1960s. However, most of them have not considered lateral heat transport, especially not in three dimensions. That sets this model built by PRL scientists apart.

The work, however, is only a first attempt towards realising a comprehensive standard lunar surface thermophysical model, the scientists say.

Significance

The renewed interest in exploring the Moon, especially by humans, elevates the significance of this study. The model may prove useful for any lunar geophysical mission in the future.

Even India’s Chandrayaan-3 mission might benefit from the model. One of the planned lander payloads, Chandra’s Surface Thermophysical Experiment (ChaSTE), will measure the thermal conductivity and temperature after it gets to the lunar surface. That data can be interpreted using the model, in combination with laboratory experiments.

Future human lunar exploration and habitation will require knowledge of the local thermal environment of any location on the Moon. This model can help with that as well.

PRL scientists were only recently involved in another lunar study, in collaboration with scientists from the United States and Japan, which suggested a new scenario for the origin of lunar basalts through the study of a unique group of lunar meteorites.

PRL Ahmedabad, founded by Dr Vikram Sarabhai, is an active participant in India’s planetary exploration programme.