Moon’s upper surface has two distinct layers within centimetres, reveals Chandrayaan-3 ‘hop’ experiment
Scientists have now revealed new details about the upper surface of the Moon at the landing site using data collected during that ‘hop’ manoeuvre performed towards the end of planned active mission life of Chandrayaan-3.
The Vikram lander before and after the hop 50 cm away from the Shiv Shakti point (Photo: Isro) THE FAMOUS ‘hop’ experiment performed by the Chandrayaan-3 lander on the Moon was not just about demonstrating Indian space agency ISRO’s ability to launch from the lunar surface. Scientists have now revealed new details about the upper surface of the Moon at the landing site using data collected during that ‘hop’ manoeuvre performed towards the end of planned active mission life of Chandrayaan-3.
In new findings published in the Astrophysical Journal, scientists from the Physical Research Laboratory (PRL) in Ahmedabad have reported that the Moon’s upper surface, the regolith as it is called, is not uniform, and its physical and thermal properties show sharp changes at just a few centimetres of depth. The loose porous layer at the top very quickly gives way to a denser compact layer just 2 to 6 cm below.
More importantly, the paper, which is based on analysis of data produced by the ChaSTE (Chandra’s Surface Thermophysical Experiment), suggests that the ‘hop’ experiment disturbed the upper loose layer enough to expose the subsequent layers to the instruments onboard the lander.
On September 4, 2023, just before it went into hibernation to survive the lunar night, the Chandrayaan-3 lander, which had made a historic soft-landing 10 days earlier, was made to perform a small jump. The lander fired its engines, lifted itself up about 40 cm from the surface, and landed again 30-40 cm away.
The ‘hop’ experiment was never publicised in the Chandrayaan-3 plans and had come as a surprise. It was seen as a demonstration of the capability of ISRO to get the lander to fire its engines and produce enough thrust to lift itself up from the surface. This capability is key for future missions in which the spacecraft would be required to make the return journey to the Earth.
The new findings have put a more precise measurement for the distance travelled by lander during the ‘hop’ experiment — about 50 cm, instead of the earlier estimate of 30-40 cm. The paper says that the rocket plume generated during the ‘hop’ was enough to blow away about 3 cm of the top layer of the surface, and allow the ChaSTE to have a look at the newly exposed layer beneath. A rod-shaped probe with a sharp tip and fitted with temperature sensors, ChaSTE was able to do a thermal profile of the new site post ‘hop’. It was deployed for 57 minutes during lunar twilight, which lasts for a few hours unlike the Earth twilight that lasts for a few minutes before sunset. The analysis revealed that even at depths of 6 to 9 cm, the lunar surface was composed of two distinct layers.
Data from instruments onboard Chandrayaan-3 mission are continuing to generate very useful information about the Moon. ChaSTE, one of the four instruments on the lander, has itself produced at least three major papers in important international publications until now.
The paper represents a first-of-its-kind thermal profile, density and layering structure of the Moon’s surface at the lunar twilight time, just ahead of sunset on this part of the Moon. The information could be useful at the time of planning future moon walks or for building lunar bases, PRL scientists said.
Specifically, the amount of displacement caused by rocket plumes at the time of the ‘hop’ experiment is very useful information for space agencies planning return missions. It helps them to understand what to expect when a rocket engine is fired so close to the surface.
Data from ChaSTE has resulted in other findings as well, which have been published earlier. Last year, the same group of scientists had reported that water-ice on the Moon could be more prevalent than understood earlier. Using ChaSTE data, they had reported that there was a good probability that water-ice was present in locations outside of the polar regions of the Moon.
In another publication, scientists had shown that temperature of the lunar surface dropped drastically with depth. At depths of just 10 cm, the temperature was about 60 degree Celsius less than at the surface. Such extreme heat non-conductivity was considered very useful information from the perspective of creating temperature-controlled habitats on the Moon.
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