Liquid water is prerequisite for extraterrestrial life. Any exoplanet to qualify as habitable would need liquid water. Till now even in our own solar system no body other than earth has been confirmed to be habitable. Man stepped on moon long ago but till now confirmed evidence of water on moon has not come to the fore. But moon is definitely best candidate other than earth to qualify as habitable. Apart from moon many other bodies are under consideration to qualify as habitable. Mars, moons of other planets and asteroids are under consideration but no conclusive evidence of hospitability has been found yet. In such a scenario search for habitable exoplanets is also on in full swing.
Search for habitable exoplanets has not been futile. Just like our solar system, most planetary systems have habitable zone but location of habitable zones of different planetary systems is different and depends on the size and brightness of the star of such planetary systems. Simply speaking, habitable zone is where liquid water can exist. Most astronomers focus on habitable zones of different planetary systems when looking for habitable exoplanets but there are other criteria.
How do astronomers look for habitable exoplanets?
They look in habitable zones of planetary systems
Universe is vast and we have to start from somewhere. This is why concept of habitable zone was developed. This concept helped limit the scope of search hugely. Scientists generally focus on exoplanets in habitable zone of planetary systems other than our solar system. No scientist will agree that finding exoplanets in habitable zone is more probable. They are simply looking for exoplanets in habitable zone of planetary systems because that is convenient, it is like looking for lost car keys under the lamp post in a dark night.
They look for earthlike planets
Astronomers often focus on exoplanets that are similar to earth. They rightly believe that gas giants like Jupiter or Saturn can’t be habitable and rocky planets like earth can be. Many rocky planets of sizes similar to earth have been detected. Some of these earth like planets are orbiting red dwarf stars. Red-dwarf stars are not very conducive to nurture of life.
They focus on sun like stars
The only star to have confirmed record of nurturing life is our sun. It has nurtured life for 4 billion years on earth and hence astronomers often focus on sun like stars to find exoplanets. But G-type yellow stars like sun are rare to find in our galaxy milky-way.
They focus on planetary systems of K dwarfs
Orange dwarfs or K dwarfs are regarded as true Goldilocks stars. Goldilocks zone is nickname for habitable zone and hence it is easily understandable what Goldilocks stars are. These stars are nor to hot nor to cold and are also not violent. These stars are touted to be most suitable for nurture of life. Such stars have long life compared to G-type stars. There are three times more K stars then G stars in Milky Way.
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