Astronomers say - A Super-Earth about 111 light-years away is the best candidate for habitability that we know right now.





Ever since the discovery of the first exoplanet in the 1990s, astronomers have made steady progress towards finding and probing planets located in the habitable zone of their stars, where conditions can lead to the formation of liquid water and the proliferation of life.





What finds about the exoplanet?



In 2009, NASA launched a spacecraft called Kepler to look for an exoplanet. Kepler looks for planets in a wide range of sizes and orbits. And these planets orbited around stars that caries in size and temperature.

Some of the planet discovered by Kepler are rocky planets that are at a very special distance from their star. This sweet spot is called the habitable zone, where life might be possible.



What is an exoplanet?



An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917, but was not recognized as such. The first confirmation of detection occurred in 1992. This was followed by the confirmation of a planet detected in 1988. As of 1 September 2019, there are 4,109 confirmed exoplanets in 3,059 systems, with 667 systems having more than one planet.





New discovery

Hubble Telescope has revealed water vapor in the atmosphere of an Earth-size planet. Although this exoplanet orbits a star that is smaller than our sun, it falls within what’s known as the star’s habitable zone, the range of orbital distances where it would be warm enough for liquid water to exist on a planet’s surface.

hubble telescope

The discovery, announced this week in two independent studies, comes from years of observations of the exoplanet K2-18b, a super-Earth that’s about 111 light-years from our solar system.



Discovered in 2015 by NASA’s Kepler spacecraft, K2-18b is unlike our home world: it’s more than eight times the mass of Earth, which means it’s either an icy giant like Neptune or a rocky world with a thick hydrogen- rich atmosphere.

This is the only planet right now that we know outside the solar system that has the correct temperature to support water, it has an atmosphere, and it has water in it.

The search for life

Are we alone in the Universe? This is a question mankind has pondered for centuries, the search is truly on to find another Earth-like world.

New evidence being compiled suggests that it’s highly unlikely that earth is unique, it is estimated there are habitable planets around 10 to 20% of the stars in our galaxy.



When you considered that there are at least 200 million stars in the Milky Way then it could possibly contain billion of worlds similar to our own.

What is an exoplanet?

All of the planets in our solar system orbit around the sun. Planets that orbit around other stars are called exoplanet. The exoplanet is very hard to see directly with a telescope. They are hidden by the bright glare of the stars they orbit.

Types of exoplanet

Gas and Ice Giants

Gas giants are planets similar to Jupiter and Saturn. Their mass is mostly composed of hydrogen and helium with possibly a dense rocky or metallic core.



Ice giants are similar to Uranus and Neptune, they have much less hydrogen and helium in their composition and more heavier elements.



Around two-thirds of the planets that have been discovered outside our solar system are either gas or ice giants.

Hot Jupiters

Hot Jupiters are gas giant planets similar in mass to Jupiter but which orbit very close to their parent star.



As a result of the close proximity to their star, their surface temperatures exceed 700C (1300F).



I t seems that Hot Jupiters are very common in our galaxy, which is not what astronomers expected as gas giants orbit in cold regions of our solar system.

Super Earths



Super Earths are ‘potentially’ rocky planets with up to 10 times the mass of Earth. The term ‘Super Earth’ simply refers to the mass of the planet and not to any planetary conditions, so some of these may actually be gas dwarfs.



The first two exoplanets to be detected were Super-Earths orbiting around the pulsar PSR B1257+12.

Free Floating Planets





Free-floating planets or orphan planets do not orbit around any star. It is believed that these isolated worlds were somehow ejected from developing systems and now free-float around the galaxy.



Although very few have been detected they are believed to very common in our galaxy.









Pulsar Planets

Pulsar planets orbit around Pulsars or Neutron Stars. These super-dense, rapidly spinning stars are the core remains of a large star after a supernova explosion.



It is highly unlikely that any orbiting planet could survive the blast from a supernova so Pulsar Planets probably formed after the event and now orbit around the dead star.

Water Worlds

Water Worlds are planets whose surfaces are entirely covered in water. Evidence suggests that these planets originally formed as objects made of ice and rock far from their parent star.



As they drifted towards the star they heated up melting the ice and so became covered in oceans. Under the surface the water is so dense its consistency is more like ice.

Chthonian Planets



C hthonian Planets were once gas giants but have migrated far too close to their parent star. As a result, their atmospheres have been roasted away, leaving only a rocky or metallic core.



It is possible their surface may be covered in molten lava. Due to their similarity to terrestrial planets, some Super-Earths may actually be Chthonian Planets.









Exo Earths

These are planets that have a similar mass, composition, radius, and atmosphere to Earth and orbit in the habitable zone of its star.



T his is an area where the temperature would allow water to flow on the planet’s surface and possibly allow life to flourish.



Although several Earth sized planets have been discovered orbiting in the habitable zone around stars their composition and atmospheric conditions are unknown. So to date, there have been no confirmed discoveries of any Exo Earths.

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What are the techniques of hunting Exoplanet?

Radial Velocity

Radial Velocity also is known as Doppler Spectroscopy is the most successful method of finding exoplanets. This technique measures how much a star wobbles due to the gravitational effects of orbiting planets.



It is not strictly true to say that planets orbit around stars, they actually both orbit around their common center of mass. As stars are much more massive than planets the common center of mass is very close to the star and very far from the planet, as a result, the star has a very slight, circular or elliptical orbit









You can see this demonstrated in the video to the right.





This wobble can be detected by measuring the light from the star as it moves back and forth from Earth.





As the star moves towards Earth its light moves very slightly towards the blue part of the spectrum, known as blue-shifting, and as the star moves away from its light moves very slightly towards the red part of the spectrum, known as red-shifting.





Of course, this is an exaggerated version of what actually happens, the shifts in the spectrum are so small only highly sensitive instruments can pick them up.



By observing these shifts over a period of time a regular pattern may emerge signaling that a planet or other object is orbiting the star.





Transit Method

The planet Venus transiting the sun

When a planet transits it is simply passing between Earth and its star, the image on the left is of a Venus transit of the Sun.



This event causes the light from the star to dim very slightly which can be detected by sensitive instrumentation.



If the dimming occurs regularly and for fixed periods of time then it is probably the star is being orbited by a planet.

The advantage of this method is that it gives more information about the planet than Radial Velocity. As the size of the star is known any dimming in its luminosity can provide a fairly accurate assessment of the planet’s size.



Also, the composition of the planet’s atmosphere can be deduced by analyzing the light that gets absorbed by elements as it passes through its atmosphere.



B y combining the results of the Transit Method and Radial Velocity an estimate of the planets size, mass and composition can be gained.