There are billions of stars and planets in the observable universe. Exoplanets are those planets which do not belong to our own solar system where the nine planets orbit our Sun.
According to the record, the first exoplanet was discovered in 1988 and it got the confirmation in 1992. After that several exoplanets were found via telescope, but it was very hard to identify them as they also orbit a Star in their system and the bright glare of the star makes the planets invisible in normal telescopes. Just like our Sun has a mass of 99.8% of the total solar system. It's brightness can easily hide the existence of the planets from a particular distance.
To identify them more accurately and to study them, Nasa in 2005 launched a spacecraft named Kepler to search for exoplanets. Kepler was designed to search for planets in a wide range of sizes and orbits. These planets orbit around stars which have different sizes and temperatures.
In any solar system there is an area which is a special distance from the star where life can be found and it is also called a habitable zone. Our earth comes under the sun's habitable zone where life exists. Kepler basically identifies the rocky planets which come under their star's habitable zone.
HOW DO ASTRONOMERS IDENTIFY EXOPLANETS?
Just like we discussed, it started with telescopes. But due to several obstacles, astronomers found a method called the wobble method. In this method, the star is not perfectly in the center of the orbiting planets. From a distance, this type of orbit makes the Star look like the star is wobbling.
This method helped to identify hundreds of planets from Jupiter-like planets to more larger planets. But smaller planets like earth or more smaller are very hard to identify through this method.
So the next generation method came which is called the transit method. In this method, when an orbiting planet crosses the front of its Star, it blocks some of the star light and the star looks less brighter than usual. During this transit, astronomers record the brightness of the star before and after the transit and by comparing them astronomers can figure out the size of the planet along with the distance of the planet from the star which also suggests if the planet is in the habitable zone where life can exist.
NASA's Transiting Exoplanet Survey Satellite (TESS) is also observing the entire visible sky to identify exoplanets orbiting the nearest and brightest stars.
TYPES OF EXOPLANETS
Billions of galaxies are there in our visible universe and A number of uncountable planets are inside them. Each planet has its own specifications, it's own interior and exterior appearance and different types of compounds.
But astronomers divided them into four categories according to our our system planets. They are-
- Gas Giant Planets
These are the planets which have the same components of the star and they are the large planets in the solar system. They don't have a solid core but melted, extremely hot can cross thousands of degrees and extreme pressure, the density is also low. In our solar system, Jupiter and Saturn are the gas giant planets.
- Neptunium Planets
These are the planets which have a solid rocky core but the outer atmosphere is made of hydrogen and helium with the size of Neptune or Uranus. Kepler identified about thousands of sub-neptunian eco planets. These are smaller than Neptune but bigger than our earth.
- Super Earth
Super earth are basically those plants which are larger than our earth but smaller than Neptune. These planets can be made of rock or gas or both. It may have an atmosphere or may not have.
GJ 15 A b is a super earth type planet which takes just 11 days to make a full orbit around the star.
55 Cancri e is another super earth planet which orbits a star named Copernicus ( 41 light years away).
- Terrestrial Planets
These planets are made of silicate, water, rock and carbon and the size is like our earth or smaller. They have atmosphere, water, ocean and maybe life as water is the important element for life. In our own solar system Mars, Earth, Venus and Mercury are the terrestrial planets. They all have atmospheres, rocky surfaces, and some have water.
IMPORTANT FACTS
Not all exoplanets orbit their Star, there are billions of planets which do not orbit any star which is named as rogue planets which may be separated from any solar system and travelling in the cosmos without any destination.
These planets are very dangerous as they are invisible because they don't have light.
|Know More About Rogue Planets|
Credit:Nasa.
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