Jupiter, the largest planet in our solar system, is a massive gas giant whose nature makes answering the question of its atmospheric thickness complex. Unlike Earth, Jupiter has no solid surface to mark a clear boundary between the atmosphere and the planet itself. The atmosphere transitions seamlessly into the liquid interior under immense pressure and heat. Defining the thickness requires establishing an arbitrary, yet scientifically useful, reference point to measure from.
Defining the Vertical Scale
To measure the atmosphere’s depth, scientists adopted the 1-bar pressure level as the conventional “surface” or zero-altitude point. This pressure is roughly equivalent to the atmospheric pressure at sea level on Earth. This 1-bar level is a theoretical boundary, providing a consistent reference for all vertical measurements. The visible cloud tops are located slightly above this 1-bar level.
The full extent of the atmosphere, measured from the 1-bar level, is vast, stretching for hundreds or thousands of kilometers. The upper atmosphere, particularly the exosphere, gradually thins out, smoothly transitioning into the vacuum of space, with the outermost edge estimated at 5,000 kilometers above the 1-bar reference point. Conversely, the atmosphere extends far downward, with pressure increasing until the gas is compressed into a fluid state. Data gathered by deep probes, such as the Galileo probe, which descended over 130 kilometers, provided direct measurements of the temperature and pressure profile.
Atmospheric Layered Structure
Jupiter’s atmosphere is vertically organized into distinct layers defined by changes in temperature. The layers, moving inward from the highest altitudes, are the Exosphere, Thermosphere, Stratosphere, and Troposphere. The Exosphere is the tenuous, outermost layer where gas density is so low that particles can escape into space.
The Thermosphere lies beneath, an extremely hot region where temperatures can reach 1,000 Kelvin due to solar and magnetic heating. The Stratosphere extends down to about 320 kilometers above the 1-bar level, characterized by temperatures that increase with height. The Troposphere is the lowest and most dynamic layer, containing the visible weather systems. This is where the Great Red Spot and the colorful, banded clouds are located, driven by the planet’s internal heat.
The Gaseous Composition
The bulk of Jupiter’s atmosphere is composed of the two lightest elements. Molecular Hydrogen (\(\text{H}_2\)) is the most abundant component, accounting for about 90 percent of the molecules. Helium (He) makes up nearly all the rest, approximately 10 percent by volume.
While these two gases dominate, trace amounts of other compounds create Jupiter’s visual spectacle. These minor components, including methane, ammonia, water vapor, and ammonium hydrosulfide, freeze out at different pressure levels to form the planet’s layered cloud decks. Chemical reactions involving these compounds, including sulfur and phosphorus, generate the striking red, white, and brown colors of the cloud bands and storms.
Transition to the Interior
The atmosphere transitions gradually into the planet’s interior, driven by intense pressure. As altitude decreases, pressure and temperature increase dramatically, compressing the molecular hydrogen gas. At a depth of roughly 1,000 kilometers below the cloud tops, the pressure is so great that hydrogen begins to behave as a supercritical fluid.
Inward, the conditions lead to a point where hydrogen atoms are squeezed so tightly that their electrons are stripped away. At depths estimated around 7,000 kilometers, the hydrogen transitions into liquid metallic hydrogen. This substance is an excellent electrical conductor, and the immense, rotating ocean of this metallic fluid generates Jupiter’s powerful magnetic field. This phase change marks the end of the atmosphere and the beginning of the planet’s deep interior structure.