Final answer:
The inner planets have atmospheres rich in carbon dioxide, having lost most of their original hydrogen-containing gases. The outer planets, particularly the gas giants, are mainly composed of hydrogen and helium and have reducing atmospheres with hydrogen-based gases and hydrocarbons.
Step-by-step explanation:
The inner planets, also known as terrestrial planets, now have atmospheres dominated by carbon dioxide (CO₂). Initially, there might have been hydrogen-containing gases such as carbon monoxide (CO), ammonia (NH₃), and methane (CH₄). However, these were largely lost as ultraviolet light from the Sun caused these molecules to break apart, and most of the light hydrogen atoms escaped into space, giving way to the oxidized atmospheres we observe today.
Contrarily, in the outer solar system, the gas giants—Jupiter and Saturn—are primarily composed of hydrogen and helium, with their overall chemistry being hydrogen-dominated. This hydrogen presence leads to a reducing environment where hydrogen combines with other elements. Consequently, these planets have atmospheres filled with hydrogen-based gases like methane and ammonia, as well as hydrocarbons like ethane and acetylene.
It is fascinating to note that despite being called 'gas giants,' the immense pressure inside Jupiter and Saturn means that their hydrogen is actually in a liquid form. Therefore, referring to them as 'liquid planets' might be more apt. Both planets have deep and complex atmospheres with various types of clouds, atmospheric motions, and weather systems.