By Stacey Mitchell | Updated Mar 24, 2022
Jupiter’s diameter is roughly 11 times that of Earth, and its mass is about 318 Earth masses. The planet contains more than twice the total mass of the other eight planets, yet it represents only about 0.1 % of the Sun’s mass. Despite its enormous size, its average density is only slightly higher than that of water, a consequence of its gaseous composition.
Unlike Earth’s layered silicate and metallic core, Jupiter is dominated by hydrogen and helium. The planet’s interior can be divided into a central rocky‑icy core with a diameter of ~24 000 km (≈15 000 mi), surrounded by concentric layers of metallic hydrogen, liquid hydrogen‑helium, and an outer cloud deck. This stratification is similar to the Sun’s composition, and Jupiter would have ignited as a star if it were 80 times more massive.
Jupiter’s atmosphere is a turbulent mix of ammonia, water vapor, methane, and other hydrocarbons. Because the planet lies far from the Sun, temperatures plunge to −202 °F (≈−145 °C) in the cloud tops and rise to 86 °F (≈30 °C) near the core, creating extreme pressure conditions that compress gases into exotic states. Above the metallic hydrogen layer lies a 621‑mile (≈1 000‑km) thick cloud layer that defines the planet’s visible “surface.”
What observers on Earth call Jupiter’s surface is actually a dynamic cloud system, not a solid ground. Standing on Jupiter would be impossible, and even a hypothetical solid surface would collapse under the planet’s immense pressure. Gravity at the cloud tops is 2.5 g, so a person weighing 100 lb on Earth would feel 250 lb on Jupiter.
