Why is Jupiter less dense than Earth despite being much larger?

Jupiter is significantly less dense than Earth because its composition is fundamentally different, consisting primarily of light gases rather than the rocky materials that make up terrestrial planets.1

While Earth is a small, rocky body, Jupiter is a gas-rich giant planet. Hydrogen constitutes at least 70 percent of Jupiter’s mass, and the planet is composed largely of hydrogen and helium—the two most abundant and lightest elements in the universe. In contrast, Earth is composed of denser silicate minerals and metals.23

The difference in density arises from how these planets formed in the solar nebula. Earth formed closer to the Sun, where temperatures were too high for volatile substances like water, ammonia, and carbon dioxide to condense into ices, leaving only rocky materials to accrete. Jupiter formed much further out, beyond the "snow line," where it could accumulate large amounts of ice and subsequently capture vast quantities of hydrogen and helium gas from the solar nebula once its core reached sufficient mass. Consequently, despite Jupiter's immense mass and the extreme internal pressure that compresses its hydrogen into a metallic state, its overall bulk density remains low compared to Earth.2314