why are the surfaces of the outer planets different from those of the inner planets?

The surfaces of the outer planets are different from those of the inner planets primarily due to their composition and formation processes in the solar system. The inner planets (Mercury, Venus, Earth, Mars) have solid, rocky surfaces made mostly of metals and silicates. They are denser and smaller because they formed closer to the Sun where temperatures were high enough to keep lighter gases from condensing, allowing only heavier materials like rock and metal to accumulate as solid surfaces. The inner planets tend to have few or no moons and no ring systems. In contrast, the outer planets (Jupiter, Saturn, Uranus, Neptune) are much larger and composed mostly of gases and ices with no solid surfaces. They have thick atmospheres of hydrogen, helium, and other gases, and are often called gas giants or ice giants. These planets formed beyond the frost line, where it was cold enough for volatile compounds like water, ammonia, and methane to condense into ices, allowing the planets to accumulate large gaseous envelopes around small rocky or icy cores. The outer planets also have many moons and prominent ring systems. Thus, the difference in surface type—solid rocky for inner planets vs. gaseous or icy with no true solid surface for outer planets—stems from their different formation zones and the availability of materials at varying distances from the Sun.