These bodies are mostly composed of hydrogen at temperatures above the “hydrogen critical point”, which means that there is no clear boundary between solid, liquid and gas.
Do gas giants have a solid surface?
The answer is that the two gas giants do not have a solid surface, and it would be impossible for a human to walk across the surface area of the planets. This would likely be the same for gas giant exoplanets, as well as the two Giant planets, Jupiter and Saturn.
They both have a solid planetary core under a thick envelope of hydrogen and helium gas. The metallic hydrogen shell (located in the middle interior) in the makes up the bulk of each gas giant, and is called metallic because the high atmospheric pressure (and the pressure of ) makes the hydrogen an electrical conductor.
Arguably, this is a misnomer, since in most of the volume of these planets there is no distinction between liquids and gases, since all components (except the solid core materials) are above the critical point, so the transition between gas and liquid is smooth. Thus, terms such as diameter, surface area, volume, surface temperature and surface density can refer only to the outermost layer visible from space.
A low-mass gas planet can have a radius similar to that of a gas giant if it has the right temperature. However, smaller gas planets and those closer to their star will lose atmospheric mass more rapidly through hydrodynamic escape than larger and more distant planets.
The cores of gas giants are thought to be made up of heavier elements at temperatures (20,000 K) and pressures so high that their properties are not yet fully understood. Arguably, this is a misnomer, since in most of the volume of all the giant planets, the pressure is so high that matter is not found in gaseous form.
The outermost part of its hydrogen atmosphere contains many visible cloud layers which are composed mainly of water and ammonia. All other things being equal, in a gas giant you would descend to the point where the density of the gas giant is equal to its density (a little over 1g cm-3 in a rough approximation), this the point at which you would be “neutrally buoyant”.
Jupiter and Saturn are made up mainly of hydrogen and helium, with the heavier elements accounting for between 3 and 13 percent of the mass. They are believed to consist of an outer layer of compressed molecular hydrogen surrounding a layer of liquid metallic hydrogen, with a rocky core probably molten inside.
As it exits through the bottom, the pressure is now intense, and it begins to get quite hot, and there is nothing but the dark abyss of increasingly dense hydrogen gas below. A spacecraft passing through the atmosphere of a gaseous planet has to contend with winds stronger than any hurricane on Earth.
With this terminology in mind, some astronomers are beginning to refer to Uranus and Neptune as Uranian planets, or ice giants, to indicate the apparent predominance of ices (in liquid form) in their interior composition. In the distant future, engineers may be able to build a spacecraft capable of withstanding the conditions of the interior of a gas giant like Jupiter, but even if they succeed, the spacecraft will not be able to fly directly through the planet.
Gas giants have an atmosphere that increases more or less continuously in density as we approach the planet’s center of mass. Therefore, the observable parts are gaseous (in contrast to Mars and Earth, which have gaseous atmospheres through which the crust can be seen). It would probably even begin to float when the density of the gas around it matched that of its body. It could be the core of a gas world like Jupiter, offering an unprecedented glimpse into the interior of one of these giant planets.
Unlike rocky planets, which have a clearly defined difference between atmosphere and surface, gas giants do not have a well-defined surface; their atmospheres simply become gradually denser toward the core, perhaps with liquid or liquid-like states in between.
do gas giants have a core?
Unlike the rocky planets, which have a clearly defined difference between atmosphere and surface, the gas giants do not have a well-defined surface; their atmospheres simply become gradually denser toward the core, perhaps with liquid or liquid-like states in between.
Jupiter and Saturn are considerably larger than Uranus and Neptune, and each pair of planets has a somewhat different composition. The core orbits so close to its parent star that a year lasts just 18 hours and its surface temperature is around 1,527C. A gas giant is a large planet composed mainly of gases, such as hydrogen and helium, with a relatively small rocky core.
However, the size of the cores allowed these planets (especially Jupiter and Saturn) to take hydrogen and helium from the gas cloud from which the sun condensed, before the sun formed and expelled most of the gas.
A searingly hot medium of highly compressed gas that thunders and crashes back and forth with the energy of a hundred hurricanes tearing apart anything not composed of solid steel like cotton candy in a raging summer storm. Now, a team of astronomers has discovered what they believe to be the rocky innards of a giant planet missing its thick atmosphere. Many of them are hot Jupiters, or massive gas giants that are very close to their parent stars.
The general theory is that the rocky core would have to have formed very early in the history of the Solar System in order to capture such a high percentage of gases. One theory surrounding the formation of gas giant planets suggests that there is almost certainly a core.
Gas giants may have a rocky or metallic core – in fact, such a core is thought to be necessary for a gas giant to form – but most of their mass is in the form of the gases hydrogen and helium, with traces of water, methane, ammonia, and other hydrogen compounds. It would be easier for such cores to form beyond the snow line, where frozen materials could stick together like a growing snowball.
The planet is made mostly of hydrogen and helium surrounding a dense core of rocks and ice, and most of its mass probably consists of liquid metallic hydrogen, which creates a huge magnetic field. Scientists are studying this category of planets to find out whether super-Earths are more like small giant planets or large terrestrial planets.
All other things being equal, a gas giant descends to the point where the gas giant’s density is equal to its own (a little more than 1g cm-3, according to one approximation), at which point “neutral buoyancy” occurs. Gas giants may have a rocky or metallic core, but most of their mass is in the form of gas (or compressed gas in a liquid state; to get an idea of what this might look like, think of the liquid mercury in a thermometer).
This indicates that gas giant planets like Jupiter and Saturn have already formed into these young planetary systems, or never will. A gas dwarf could be defined as a planet with a rocky core that has accumulated a thick envelope of hydrogen, helium, and other volatiles, resulting in a total radius of between 1.7 and 3.9 Earth radii.
These four large planets, also called Jovian planets after Jupiter, reside in the outer part of the solar system, beyond the orbits of Mars and the asteroid belt. It may be more likely that the gas giants develop farther from their parent star, beyond a boundary called the snow line, where it is cold enough for ice and other solid material to form.
What this means is that, rather than being completely solid, this core is very likely to have a solid and liquid consistency.