Gas Giant

 A gas giant is what?

A massive planet primarily made of helium and/or hydrogen is referred to as a gas giant. These planets feature swirling gases atop a solid core rather than hard surfaces, similar to Jupiter and Saturn in our solar system. Exoplanets that are gas giants can be far bigger than Jupiter and orbit their stars much more closely than any planets in our solar system.

Our knowledge of the formation and evolution of planets for the most of human history was based on the eight (or nine) planets in our solar system. But during the past 25 years, more than 4,000 exoplanets, or planets outside our solar system, have been found, and this has completely transformed everything.

Helium and/or hydrogen make up the majority of gas giants in our solar system, such as Jupiter and Saturn. "Hot Jupiters" are gas giants that are located closer to their stars. Within these broad groups is much diversity. For example, hot Jupiters, which are gas giants like Jupiter but orbit their stars so closely that their temperatures soar into the thousands of degrees, were one of the first exoplanet types to be discovered. These massive planets have such close-knit orbits that they pull their stellar hosts in one direction or the other, causing a measurable shift in the spectrum of the stars' light. In the early days of planet hunting using the radial velocity method, that made hot Jupiters easier to detect.

Discover some gas giants

KELT-9 b                                                       Kepler-7 b

These gas-dominated planets, which resemble Jupiter in size, orbit their parent stars very closely, sometimes in just 18 hours. They are unlike anything in our own solar system, where the planets nearest to the Sun are rocky and circle at a great distance. As massive as the planets themselves, the mysteries surrounding hot Jupiters include whether they originate near to their stars or further out before moving inside. What would it tell us about the past of the planets in our own solar system if these giants did migrate?

Scientists will need to see a lot of these hot giants very early in their creation in order to provide answers to those issues. Our knowledge may increase with the discovery of the exoplanet HIP 67522 b, which is believed to be the newest hot Jupiter yet discovered (in June 2020). The hot Jupiter is probably only a few million years younger because it circles a well-studied star that is about 17 million years old; most hot Jupiters are more than a billion years old. The planet orbits its star, which has a mass comparable to the Sun's, in around seven days. HIP 67522 b, which is only 490 light-years away, has a diameter that is roughly 10 times that of Earth or comparable to Jupiter. Its size clearly suggests that it is a planet where gas predominates.

The discovery raises the possibility of discovering more young hot Jupiters and gaining knowledge about the formation of planets throughout the cosmos.

Giants moving?

The three basic explanations for how hot Jupiters approach their parent stars are as follows. One is that they merely gather there and remain. But in such a hostile environment, it's difficult to envisage planets forming. In addition to vaporising most elements due to the intense heat, young stars frequently undergo tremendous explosions and stellar winds, which could scatter newly formed planets.

It may be more likely that gas giants form farther from their parent star, past a line known as the snow line, where the temperature is low enough for the formation of ice and other solid minerals. Jupiter-like planets have solid cores despite being virtually entirely made of gas. Past the snow line, where frozen elements may stick together like a developing snowball, such cores would be simpler to create.

The other two theories presuppose that this is the case and that hot Jupiters subsequently move in closer proximity to their stars. What would be the migration's cause and timing, though?

According to one theory, hot Jupiters start their journey early in the history of the planetary system, when the star is still encircled by the disc of gas and dust that the planet and star both formed from. In this case, the gas giant's orbit may be disrupted and it may migrate inward as a result of the disk's gravity interacting with the planet's mass.

According to the third theory, hot Jupiters approach their star later, when the gravitational pull of nearby planets can accelerate their migration. This third idea is probably not applicable in this situation because HIP 67522 b is already so near to its star so soon after it formed. The question of how they all develop, however, cannot be answered by one hot, youthful Jupiter.