Noctilucent clouds, also known as polar mesospheric clouds, form in a part of the Earth's atmosphere, located in the mesosphere at altitudes of around 76 to 85 km above the surface of our planet in the summer months at high latitudes (±50° and ±70°). They are illuminated by sunlight when the lower layers of the atmosphere are in the darkness of the Earth's shadow. The sky at 85 km altitude is space-black. It is the realm of meteors, high-energy auroras and decaying satellites. NLCs are made of tiny ice crystals 40 to 100 nanometers wide – just the right size to scatter blue wavelengths of sunlight. These high-flying clouds form when water-ice crystals condense on particles of meteoritic smoke – tiny bits of debris from meteors that have burned up in our atmosphere. Previous studies showed that water vapor released into the atmosphere by space shuttle launches can cause an increase in noctilucent clouds near the poles and in present times by an increased space traffic-rocket launches (https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2022EA002217). 

Source: NASA