A recent finding by Indian Space Research Organisation says:
“When a helicopter lands on an open field, it kicks off a dust storm and particles are strewn all across the vicinity of the landing spot. Likewise, when the Chandrayaan-3 lander touched down on the Lunar surface by using its on-board engines (helicopters use rotors, aerospace vehicles use mini-rocket engines), it kicked up quite a lot of dust.”
It is understood that the landing rocket plumes must have displaced a significant mass of lunar epiregolith (soil/dust) during the final stages of landing and the consequent impact of the lander on the Lunar surface.
According to the findings published in the Journal of the Indian Society of Remote Sensing, the comparison of pre-landing and post-landing imaging data depicts a halo around the landing site, thereby indicating the spread of the lunar dust that had been kicked up.
Why the lunar dust would take more time to settle than that at Earth?
On the surface of the earth, owing to the effect of gravity and an atmosphere, the dust kicked up by the helicopter rotors would settle down within a few seconds of the rotor blades coming to a halt.
However, lunar gravity is barely 1/6th that of the earth and there is no atmosphere or air, therefore, the lunar dust would take a while to settle.
How much lunar epiregolith mass has been ejected by the Vikram lander?
Given the fine-grained nature of the lunar epiregolith at the Vikram landing site, a large volume of in situ epiregolith has been displaced from the landing site region.
Based on calculations incorporating the mass of the Vikram lander, approximately 2.06 tonnes of lunar epiregolith mass has been ejected. This number benchmarks well against the estimates from the much heavier Apollo landers, where around 4.5 to 6 tonnes of ejecta was displaced.
By analysing the images of the landing site and the lander, as captured by the Chandrayaan-2 orbiter, an approximate area of 108.4 meters squared, is estimated to be covered by the lunar dust scattered by the landing sequence of the Vikram lander.
Why it is important to better understand the effects and specific nature of Lunar dust?
The high-speed ejecta (lunar dust) scattered by landing lunar crafts could cause harm to even crafts circling the moon and future lunar space stations.
Larger and heavier lunar landers that spew bigger plumes of exhaust flame, could scatter more dust and accelerate these particles even outside of the moon(to lunar orbit), given the weak lunar gravity.
As more robotic and crewed Lunar missions are to reach the Lunar surface in coming years, it is of paramount importance for space agencies to better understand the effects and specific nature of Lunar dust, in order to develop methods to safeguard from it.
Lunar dust is known to cause damage to spacecraft components, sensors, cameras, space suits etc.
Given that more powerful and large landers would be touching down on the lunar surface, it would be necessary to know how fast and how far lunar dust can get ejected, the paths it may travel in, the duration it may remain afloat, and the damage it can cause to probes on the moon and those in different orbits around the moon.
Particles generally stay aloft for longest when launched from the Equator and stay aloft shortest when launched from the South Pole of Moon. Dust particles ejected from the Lunar equator at certain speeds are known to remain afloat for almost a month, whereas those ejected from the south pole would remain aloft for about a week.
