Jupiter’s interior conditions allow for the existence of liquid hydrogen despite the low critical temperature of hydrogen through a combination of high pressure and temperature found deep within the planet. In the context of gases, the critical temperature is the point beyond which a gas cannot be liquefied regardless of the pressure applied. For hydrogen, this temperature is extremely low, around -240 degrees Celsius, meaning under normal conditions on Earth, hydrogen remains gaseous or solid.
However, the conditions in Jupiter’s atmosphere and interior are far from normal. The immense gravitational force of Jupiter generates incredibly high pressures and temperatures in its inner layers. Deep inside the planet, below the thick atmosphere primarily composed of molecular hydrogen and helium, the pressure can reach millions of times that of Earth’s atmosphere. Under such extraordinary conditions, hydrogen behaves differently than it would at surface pressures.
In these extreme environments, molecular hydrogen can transition into a liquid metallic state. Initially, molecular hydrogen is compressed into a dense liquid form, and as it moves deeper, under further pressure, it becomes metallic. This state is not achieved solely by temperature considerations but rather by the immense pressures that offset the low temperature requirement for liquefaction. Consequently, Jupiter’s unique internal dynamics create an environment conducive to the existence of liquid hydrogen, despite the conventional understanding of its critical temperature.