Is there another Earth in the Universe?

Is there another earth in the universe? Are we alone here? These are some questions humans are always curious about. The fact is we can not deny the possibility of being another life out there on some planet, some millions of light years away. The question is if there is another Earth-like planet in the universe can we go there and build a new habitat for us?

How can we determine if a planet’s atmospheric conditions are ideal for living organisms or not?

NASA defines the principle habitability criteria for planets with conditions that are favorable for development of complex organisms and energy sources to sustain metabolism. Planetary habitability is the measure of a planet's or natural satellites' potential to develop and maintain environments hospitable to life. The planetary habitability is the observational estimation depending on the conditions on Earth and characteristics of the sun and solar system which is favorable for flourishing life. To determine the habitability potential of a body, studies focus on it’s bulk compositions, orbital properties, atmosphere and potential chemical interactions. Stellar characteristics include mass and luminosity, stable variability, high metallicity, rocky, wet-terrestrial type planets and moons which are having earth like chemistry are considered for life possibilities.

From Kepler space mission data scientists have found that there are 40 billion earth sized planets which are orbiting in the habitable zone of their stars within the Milky way Galaxy itself! As of now a total of 60 potentially habitable exoplanets have been found. The nearest such exoplanet is probably 12 light years away from Earth.

Planetary Habitability begins with the host star. The temperature range for habitable stars is from 7000K to 4000K. With some characteristics as they must emit the ultraviolet radiation which triggers the important atmospheric chemistry, also they must emit sufficient radiation consisting of wavelengths at which photosynthesis carries. The planet to be considered for having life on it must be in a habitable zone (HZ). A Habitable zone is a shell-shaped region of a space surrounding a star in which a planet could maintain liquid water on its surface.

There are several conditions for exoplanets to be considered as habitable and let’s discuss some of them. Low mass planets are not considered suitable for habitability because due to less gravity the atmosphere could not sustain or have thin atmosphere and smaller planets have lesser diameters and thus they lose their energy very quickly and become geologically dead. The radius of a potentially habitable exoplanet would range between 0.2 to 2.5 times Earth radii. Stability is the critical consideration in evaluating the effect of orbital and rotational characteristics of a planet on planetary habitability. As a planet's orbit decides the temperature variation on a planet and rotation decides the seasons formed on a planet. Habitability is also influenced by the architecture of planetary system around the star. There are geological factors that affect the habitability on a planet like formation of the planetary dynamo(creation of magnetic field around plant) which protects from harmful cosmic radiation and some specific geochemistry required for life flourishment.

An international team of astronauts has found signs that habitable planet may be present in Alpha Centauri, a binary star system which is 4.37 light years away from earth. There are two sun like stars Alpha Centauri A and B form a tight binary orbit around each other. Astronomers get the signals from the habitable zone around the stars. But planet’s existence is not verified yet. The figure below shows the potentially habitable exoplanets and their distance from Earth.

So it is a still a question for us that does we are all alone in this big universe? And answer of this question definitely be interesting one!!!