What is the meaning of exoplanet? It is a planet that orbits a star outside our solar system.

There are thousands of exoplanets discovered in the past 20 years. Most of them by Nasa's Kepler Space Telescope. These worlds come in different sizes, some are gigantic and some are small like Earth.

What we are interested is the Goldilock zone or the Habitable zone where the temperature permits liquid water oceans. However, the earlier definition of this zone was based on simple thermal equilibrium but current definition may encompass other factors like greenhouse effect of the atmosphere. This makes the definition of habitable zone blurr or not clear.

Recently discovered 7 worlds close to Earth's size which might be in Goldilock zone orbiting around a faint star in Constellation Aquarius. It's the first time this many Earth-size planets are discovered and there is possiblity of finding alien life form on these planets. The star is cold and small, thus these planets could be temperate meaning there could be liquid water and perhaps life on them. (Credit: space.com & theguardian.com)