Astronomers revealed about Gliese 581d in 2009 with the exoplanet being described as a super-Earth that has the possibility of harboring liquid water on its surface. A 2014 research, however, has casted doubts about the existence of this alien world with the study suggesting that the data that was used to find it may have been misinterpreted signals from the stars.

Although nearly 2,000 extraterrestrial worlds beyond the solar system have so far been discovered, the search for a true Earth analog remains to be in its infancy so some exoplanets discovered were technically not discoveries at all but mere noise in astronomical data sets.

For the same reason, researchers who revisited the evidence of Gliese 581d dismissed the existence of the planet as a stellar activity that masquerades as a planet. The exoplanet was detected after astronomers used a spectrometer to measure the small changes in the wave length of the light from the red dwarf star that Gliese 581d orbits and which is believed could host four other additional planets.

In a new study, Guillem Anglada-Escudé and Mikko Tuomi, from the Centre for Astrophysics Research at the University of Hertfordshire in the U.K., contend that the statistical techniques that were used to discount the existence of the exploplanet is not adequate for a planet of its size. Gliese 581d, believed to sit in the habitable "Goldilocks zone," has about seven times the mass of the Earth and is twice as big. It also has a surface gravity about two times that of our planet.

Although the method used to discount the exoplanet's existence has worked with larger planets in the past since the effect on the star was significant enough to negate errors in the results, it is nearly impossible to find the smallest planet signals that are close to or within the noise that is caused by stellar variability.

"We point out that their analysis using periodograms of residual data is inappropriate and promotes inadequate tools. Because the claim challenges the viability of the method to detect exo-Earths, we encourage reanalysis and a deliberation on what the field-standard methods should be," the researchers wrote.

The researchers of the new study, published in the journal Science on March 6, used a more accurate model on the data and said that despite stellar variability, they are confident that the GJ 581d signal is a real one. Other experts expressed enthusiasm on finding life on the exoplanet.

"The Gliese system is particularly exciting to us as it's very close to Earth, relatively speaking. So with future generations of telescopes, we'll be able to search for life on Gliese 581d directly," said Robin Wordsworth, from the Institut Pierre Simon Laplace in Paris.