The rocky planets themselves are divided into two categories: small rocky planets and so-called super-Earth planets. Small rocky planets are the type of planets that are also found in the solar system. Although the rocky planets in the solar system differ from each other, they all fall into one category.

However, exoplanets do not exist in the solar system, yet they are one of the most common planets in the Milky Way. These planets, as their name suggests, are a kind of rocky planet larger than Earth. According to a more precise definition, the rocky exoplanets are at least twice the size of Earth.

The mass of super-Earths can reach up to ten times the mass of the Earth. Scientists still do not know at what point the planets lose their rocky surface and become gas planets. However, in the range of 3 to 10 times the mass of Earth, there may be super-Earths with different compositions, such as blue worlds, snowball worlds, or even planets like Neptune that are made of very dense gas. As a result, heavy super-Earths that have turned into gas giants can be classified as sub-Neptunian or mini-Neptunian planets.

Gas giants are divided into three categories: gas giants, ice giants, and hot Jupiters. Simple gas giants are called worlds like Jupiter and Saturn. These heavy worlds are usually located in orbit far from their star, have dense atmospheres mostly composed of hydrogen and helium, and do not have a solid surface.

On the other hand, planets like Uranus and Neptune are called ice giants. Although the predominant composition of all gas giants is hydrogen and helium, ice giants are a type of gas giant with ice concentrations in their atmosphere. For example, both the planets Uranus and Neptune have large amounts of chemicals such as methane, ammonia, and water. Ice giants are usually located in the outer reaches of their star system; Where ice is found in high concentrations.

Gas giants and ice giants can be seen in the solar system. However, the third type, hot Jupiter, does not exist in our solar system. A hot Jupiter is a gas giant that is in a very close orbit from its parent star. This orbit can be even closer to the Sun than the orbit of Mercury; Therefore, hot Jupiter planets usually have hellish temperatures in their atmospheres, hence the nickname hot Jupiters.Introduction of extrasolar planets

The planet TOI-1452b is located in the orbit of a red dwarf star at a distance of 100 light-years from Earth. Researchers discovered this planet through the blocking of starlight and its fluctuations.

Based on the obtained information, the planet TOI-1452b is almost 70% larger than the Earth and therefore it is included in the group of super-Earth planets. The planet also orbits its star once every 11 days. The density of this planet indicates that it has a liquid ocean surface as well as rocky and metallic compositions like planet Earth. Surprisingly, water makes up 30% of TOI-1452b’s mass. While water on earth is only 1% of its mass.

The James Webb Telescope’s Near-Infrared Spectroscopy (NIRSpec), closely observing the exoplanet WASP-39b, found clear evidence of carbon dioxide in its atmosphere. This is the first time that this familiar gas has been discovered on Earth in a planet outside the solar system. The spectrum of 3 to 5.5 microns, which is the infrared ratio of the transmission spectrum, is useful not only for detecting carbon dioxide but also for water and methane, which are all indicators of life.

WASP 39b, with a temperature of 870°C, is a hot Jupiter-type planet about 700 light-years from Earth. The mass of this planet is equal to a quarter of the mass of the planet Jupiter, but its diameter is 1.3 times larger than Jupiter. The planet also orbits a Sun-like star at such a high speed that it completes its orbit in just four days.

WASP-103b, shaped like a rugby ball, is the first non-spherical exoplanet ever discovered. This planet, which completes its orbit around its star in less than a day, has strong gravitational forces that have turned it into a rugby ball.

The Cheops telescope of the European Space Agency discovered this strange planet in the constellation of Hercules. The planet WASP 103b, twice the size of Jupiter, is very close to its star.

Although 51 Pegasi b is not the first exoplanet discovered, it can be considered the first example discovered around a Sun-like star. In addition, this planet has no resemblance to the planets we know. This huge world completes its star orbit in just a few days.

In 2015, the atmosphere of 51 Pegasi b was studied in the visible spectrum. As a result, researchers were able to find out the real mass or orbital orientation of this planet through its light.

The name PSR B1620-26b may not be as easy to pronounce as many exoplanets. However, this planet, with an approximate age of 12.7 billion years, is the oldest planet ever discovered. This planet is only slightly younger than the age of the entire universe. This ancient planet orbits a pulsar as well as a superdense white dwarf at the same time. These two stars revolve around each other and the gas giant planet also revolves around their gravitational axis.

The planet Gliese 876d is only 15 light-years away from Earth, and due to its small size, it belongs to the group of rocky planets. Of course, this planet is slightly bigger than our Earth. By all accounts, Gliese 876d is a hell of a world. This planet is very hot, yet since its discovery in 2005, it has been considered important evidence for the existence of rocky worlds outside the solar system.

There is a problem with the classification of smaller exoplanets; So far, we have observed several planets in space that are larger than Earth but smaller than Neptune; But we don’t have such a group in the solar system. For this reason, it is difficult to guess that rocky planets like Mars and Earth can grow to what extent? Or exactly in what dimensions do they become gas giants like Uranus and Neptune?

Kepler 11f is a mini-Neptune planet. The density of this planet shows that it has an atmosphere similar to Saturn and a small rocky core. This planet led to the creation of a new category called gas dwarf, which does not exist in our solar system.

Kepler 452-b can be considered the most Earth-like planet ever discovered. The star of this planet is the same size as the sun and its year is slightly longer than the Earth’s year. Of course, this planet is slightly larger than Earth, but it is definitely located in the life belt of its star.

However, there are a few problems with Kepler 452b: First, the planet is more than 1,000 light-years away from Earth, so we’ll never reach it. It is also 1.5 billion years older than Earth, so it can be said that its host star has grown so much that it has made the planet uninhabitable. So maybe it was Earth’s twin many years ago.

One of the biggest questions of mankind is whether there is life outside the earth. The James Webb Space Telescope, launched in 2021, has found evidence of the essential ingredients for extraterrestrial life: a mixture of gases in the atmospheres of Earth-like exoplanets. This telescope was able to discover atmospheric signs similar to Earth, such as oxygen, carbon dioxide, and methane, which are strong indicators of possible life.

Probably, future telescopes will be able to detect the signs of photosynthesis, which is the conversion of sunlight into chemical energy necessary for plants. Or maybe they can detect gases and molecules from animal life. Also, extraterrestrial intelligent life probably creates atmospheric pollution that can be detected from a distance.

So far, more than 5,000 exoplanets have been discovered, but their total number can reach trillions. One of the best tools for scientists to increase the accuracy of searches is the area known as the life belt. As we said in the previous section, the life belt is a distance from the orbit of a star whose temperature is suitable for the flow of surface liquid water.

Many other conditions are necessary for the formation of life on exoplanets: first of all, the size of the planet and the right atmosphere are important. Also, the host star must be stable and not emit deadly flares. Lifebelt is just one way to narrow down searches. So far, many Earth-like planets have been discovered, however, more advanced tools are needed to increase the accuracy of searches.

According to estimates, the number of Earth-like planets in the Milky Way alone reaches ten billion. Kepler 22b was discovered in 2011 as the first exoplanet in the habitable belt. When the news of this discovery spread, people immediately fantasized about life on such a planet. However, the distance of 587 light years from Earth means that we have to spend thousands of years to reach this exoplanet. This planet is currently under investigation.