Final answer:
The characteristic common to all inner planets is that they have rocky surfaces, which is different from the gaseous outer planets with rings and moons. Geological activity has played a critical role in shaping their distinct terrains.
Step-by-step explanation:
The characteristic common to all inner planets is that they have rocky surfaces. Unlike some of the outer planets, which are gas giants with extensive systems of rings and moons, the inner planets are made of rock and metal and lack such rings. Their proximity to the Sun means that any volatile compounds would have been burned off or escaped their gravitational pull, contributing to a primarily rocky composition. Their size and the heat from the Sun have prevented them from retaining extensive gaseous envelopes like those of the outer planets, leading to differentiated, rocky worlds. The terrestrial planets, Earth, Venus, Mars, Mercury, and the Moon, have all evolved differently based on their mass, composition, and distance from the Sun. Geological activity on these planets, such as volcanism and tectonic movements, has shaped their surfaces over time.