Final answer:
Water ice at the poles of the Moon and Mercury is likely due to comets and asteroids depositing water, which froze in cold, shaded areas. This discovery has implications for potential human habitation and space exploration.
Step-by-step explanation:
The presence of water ice on the Moon and Mercury's poles is believed to be the result of comets and asteroids hitting their surfaces and depositing water. Some of this water froze in extremely cold regions, known as cold traps, where sunlight doesn't reach, such as deep craters at the poles. The extreme cold temperatures in these shaded areas allow the water to remain frozen as ice. This discovery is significant as it opens up the possibility of future human habitation on the Moon or as a base for further space exploration.