A nozzle, even with low exit pressure, acts as an under-expanded nozzle when it operates in a vacuum environment like the lunar surface. The exhaust gas expands rapidly after leaving the nozzle, resulting in a radial flow rather than being confined. In this case, shear stress (tangential force) dominates over normal force (pressure), leading to erosion spreading outward instead of downward. Imagine a scenario where you land a lander in the Earth's environment and the Moon's environment with the same exhaust pressure, temperature, etc. For Earth conditions, the atmosphere confines the flow, and a crater is expected to form beneath the nozzle. On the Moon, the flow expands radially due to the vacuum, leading to erosion in a more lateral direction. This radial erosion was observed during the Apollo missions, where no crater was formed beneath the lander, but dust cast out radially at high speeds and damaged the Surveyor mission’s optical mirror, even though it was located away from the Apollo landing site. In short, due to vacuum environment it creates less damage than it would create in atmospheric conditions like Mars and Earth. Ofcourse, you need take care of ground conditions like compact, rocks, porosity, cohesive strength of soil, etc.
Because of the absence of air, the heat would dissipate more slowly than it would in atmospheric conditions. In space, the primary method of heat dissipation is radiation.
In vacuum conditions, the exhaust would not slow down. When you land on an asteroid or Moon, the gas expands radially, but still, the centre flow goes straight and creates a shock. You will be seeing a bow shock structure in the lunar environment (you can refer to this paper to learn more on how it forms: https://pubs.aip.org/aip/pof/article-abstract/33/5/053307/1076639/Modeling-of-dusty-gas-flows-due-to-plume?redirectedFrom=fulltext). These shocks cause the exhaust to slow down only after impinging on the ground, converting kinetic energy into heat, leading to localized erosion or heating.
