Mega Giant Planets of Our Solar System
By: Zeba Academy
Tags: Planets, Earth, NASA, Solar System, The Sun

Giant planets are large planets, which are around 10 or more times the mass of Earth. They are also predominantly made of liquid or gas, notably hydrogen and helium. They are primarily composed of low-boiling-point materials such as by gases or ices. And there are four known giant planets in the Solar System namely Jupiter, Saturn, Uranus, and Neptune.

Giant planets are also termed as Jovian planets, after Jupiter. They are also termed as gas giants. However, many astronomers now apply the term gas giants only to Jupiter and Saturn, representing Uranus and Neptune, which have different compositions, as ice giants.

Formation

Primarily, all of the giant planets comprise of fluids above their critical points, where distinct gas and liquid phases do not subsist. A giant planet is a massive planet and they may have a heavy molten core of rocky elements, or the core may have fully dissolved and dispersed throughout the planet if the planet is hot enough. The principal components in the case of Jupiter and Saturn are hydrogen and helium, whereas water, ammonia, and methane in the case of Uranus and Neptune. The term gas giant was coined in the year 1952 by the science fiction writer James Blish and was primarily used to refer to all giant planets.

Giant planets are commonly considered to be deficient in solid surfaces, but it is more valid to say that there is an absence of surfaces altogether as the gases that comprise them simply keep on turning thinner and thinner with increasing distance from the center of the planets, finally becoming indistinguishable from the interplanetary medium. Therefore, landing on a giant planet may or may not be possible, depending on the size and composition of its core.

Exoplanets

Extrasolar giant planets that are considered to orbit very close to their stars are known to be called the exoplanets that are quite easy to detect. These are also termed as hot Jupiters and hot Neptunes since they have very high surface temperatures. Until the advent of space-borne telescopes, Hot Jupiters were observed to be the most common form of exoplanets known, because of the relative ease of spotting them with ground-based instruments. Jupiter and Saturn both have a radius in the range of 60,000 km to 72,000 km, while Uranus and Neptune are somewhat smaller with a radius of approximately of the Earth.

Basic facts

The giant outer planets Jupiter, Saturn, Uranus, and Neptune are by far the largest planetary bodies in the solar system and together they constitute around 99.56% of the planetary mass. Although they remain very far from the Earth, the huge physical size of Jupiter and Saturn were still easily visible to the ancients. However, the other two “giants”, Uranus and Neptune, are notably smaller and so much farther from the Earth that they were unknown before the advent of telescopes, although Uranus is in fact just visible to the naked eye. Uranus was discovered by accident in the year 1781 by William Herschel.

All the giant planets are observed to rotate very quickly and the shape of the planets shifts under the centrifugal forces that arise. Hence, all the giant planets are notably secluded, especially Jupiter and Saturn, with the pole-to-pole diameter being less than the equatorial diameter. Another key difference between the inner terrestrial planets, such as the Earth, and the giant planets is that the giant planets have remarkably low densities, which are roughly equal to water and similar to that of the Sun, which has a density of 1.41 g cm. Thus, while we know that the Earth is a rocky body, the outer planets must be composed predominantly of much lighter materials. In fact, the giant planets are now known not to have a solid rocky “surface” at all, but instead are gaseous in nature throughout.

The core nucleated accretion model anticipated a fusion of planetesimal accretion and gravitational accumulation of gas. According to this model, the initial stages of growth of a gas giant planet are identical to those of a terrestrial planet. Dust settles towards the midplane of the protoplanetary disk, agglomerates into kilometer-sized planetesimals, which continue to expand into larger solid bodies via pair-wise inelastic collisions. Along with the growth of the planet, its gravitational potential gets deeper, and when its escape speed also begins to go beyond the thermal velocity of the gas in the surrounding disk. It further begins to gather a gaseous envelope. The gaseous envelope is primarily optically thin and isothermal with the surrounding protoplanetary disk, but as it acquires mass it becomes optically thick and hotter with increasing depth. While the planet’s gravity pulls gas from the surrounding disk towards it, thermal pressure from the existing envelope limits accretion.

For much of the planet’s growth epoch, the primary limit on its accumulation of gas is its tendency to radiate away the gravitational energy provided by accretion of planetesimals and envelope contraction; this loss of energy is important for the envelope to further contract and allows more gas to reach the surface in which the planet’s gravity dominates. The size of the planet’s gravitational domain comprises of a greater fraction of the planet’s Hill sphere, whose radius, RH, is given by:

RH = M 3M? 1/3 r

In this case, M and 3M are the masses of the planet and star, and r is the distance between these two bodies. Finally, increases in the planet’s mass and radiation of energy allow the envelope to shrink rapidly.

Facts based on recent research

Jupiter: NASA’s Juno spacecraft, in the year 2016 studied the planet’s rings, which was hard to attain because they are far fine concept than that of Saturn. Juno discovered that the elements regulating the auroras of Jupiter are different than those on Earth. It also disclosed some important insights about the atmosphere, such as finding snow emanating from high-altitude clouds. Meanwhile, scientists using the Hubble Space Telescope conducted detailed studies of Jupiter’s Great Red Spot, watching it shrink and intensify in color.

Saturn: The Cassini spacecraft enveloped up more than a dozen years of examination at Saturn in the year 2017. But the science Cassini which was conducted is still very much in progress since the scientists examined work from its many years at Saturn. In its latter months, the mission analysed Saturn’s gravity and it’s magnetic fields, looked at the rings from a different angle than before, and dived into the atmosphere by design, that is, a move that will showcase more about the structure of the atmosphere.

Uranus: The storms of Uranus are a frequent target for both professional telescopes as well as amateur astronomers, who observe how they change and grow over time. Scientists are also intended in learning about the structure of its rings, and what its atmosphere comprises. Uranus may also have several Trojan asteroids, that is, the asteroids in the same orbit as the planet. The first of which was discovered in the year 2013.

Neptune: The superstorms on Neptune are also examined as a remarkable target. In the year 2018, those examinations bore fruit again as the work from the Hubble Space Telescope showed that a long-standing storm is now contracting. The researchers also observed that the storm is disappearing differently than what their models expected, which shows that our understanding of Neptune’s atmosphere still requires some form of refinement.