The planetary body primarily made of gas and lacking a solid surface is Jupiter. As the largest planet in our solar system, Jupiter is primarily composed of hydrogen and helium. It is classified as a gas giant and possesses a thick atmosphere that features impressive cloud bands and storms, including the famous Great Red Spot. Unlike terrestrial planets, which have solid surfaces, gas giants like Jupiter do not have a defined surface and instead deepen into liquid and metallic states of hydrogen under immense pressure, showcasing the vastness and complexity of our solar system.