Scientists have made the first exoplanet discovered in 2007 in a habitable or ‘Goldilocks Zone’, a prime candidate in the search for alien life.

The exoplanet Gliese 581d is located only 20 million light years from Earth. Following its discovery, it was named as ‘super-Earth’ as it holds the possibility of supporting liquid water and microbial life on its possibly rocky surface. The mass of the planet is around seven times that of the Earth.

Gliese 581d orbits around Gliese 581, a red dwarf star in the constellation Libra. It is in the ‘Goldilocks Zone’, known technically as the ‘Circumstellar Habitable Zone’ or simply the ‘Habitable Zone’ as it’s the zone around a star within which a planet could have sufficient atmospheric pressure and liquid water to support life.

In the zone, the temperature is just right for water to exist in liquid form as the water is not so hot nor so cold. When the planet was discovered, France's National Center for Scientific Research said that the climate of Gliese 581d is not only stable against collapse but warm enough to have oceans, clouds and rainfall.

However, when researches from the Queen Mary University of London (QMUL) and the University of Hertfordshire examined Gliese 581d more closely in 2014, they concluded that the planet wasn’t actually there and it was all an observational flaw mixed with some noise in the signal.

The planet orbiting Gliese 581 was detected by an astronomical technique known as the ‘radial velocity method’ that measured the very slight frequency shift (Doppler shift) of light from the star caused by a nearby planet.

Guillem Anglada-Escudé and Mikko Tuomi, from the Centre for Astrophysics Research at the University of Hertfordshire in the U.K., argued that statistical techniques used to discount the existence of the exploplanet were not adequate for a planet of its size.

However, the study claims that planet does exist, which further underlined the matter of habitability. The QMUL team used a more accurate model with existing data and reclassified Gliese 581d as one of the most probable exoplanets to harbor life. Their study results were published in the journal Science on March 6.