Fill in the missing letters in the paragraph.
The number of underlines shows how many letters you need to fill in. You may answer with the full word or only the missing part.

Differences among the planets of our so_ _ _ system reflect variations in composition, distance from the Sun, and atmospheric conditions. Mercury, loc_ _ _ _ closest to the Sun, experiences extreme temperature shifts because it lacks a substantial atmosphere. Venus, by contrast, is surrounded by a dense atmosphere rich _ _ carbon dioxide, resulting in an intense greenhouse effect. Mars shows evidence of past water activity, suggesting that its climate was once more hab_ _ _ _ _ _ for life. Beyond the asteroid belt, Jupiter and Saturn differ fundamentally from the inner planets, as they are composed prim_ _ _ _ _ of gases and possess numerous moons and ring systems. Together, these contrasts illustrate how plan_ _ _ _ _ characteristics are shaped by both formation history and environmental factors.