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Illustration: exoplanet Gliese 581d

Astronomers believe mysterious signals - previously dismissed as stellar bursts - are coming from an Earth-like planet.

The Gliese 581d planet has conditions that could support life, and is likely to be a rocky world, twice the size of Earth.

Signals from the planet were initially discovered in 2010, but last year dismissed as "noise" from distant stars.

Two whole planets that were potentially habitable were dismissed by a study in the journal Science – 581d and 581g, which were discovered at different times orbiting their host star.

But a new study published in the same journal wipes the slate clean again and criticizes the previous one as “inappropriate” and “promoting inadequate tools.” Revisiting the ‘flawed’ data dismissed by Pennsylvania State University, a team from Queen Mary University of London (QMUL) and University of Hertfordshire proved that just a minor tweak to the technique makes a difference.

Previous methods could account for only larger celestial bodies, where calculations did not have to be as painstaking and smaller errors went unnoticed, because of the very obvious effect of the planet on the star’s light. That is according to Dr Guillem Anglada-Escudé, who authored the new paper.

"The existence, or not, of GJ 581d [Gliese 581d] is significant because it was the first Earth-like planet discovered in the 'Goldilocks'-zone around another star and it is a benchmark case for the Doppler technique,” he said of the method used to detect spectral shifts in the wavelength of a star’s light.

"There are always discussions among scientists about the ways we interpret data but I'm confident that GJ 581d has been in orbit around Gliese 581 all along. In any case, the strength of their statement was way too strong. If their way to treat the data had been right, then some planet search projects at several ground-based observatories would need to be significantly revised as they are all aiming to detect even smaller planets. One needs to be more careful with these kind of claims."

As part of their advice in the new paper, Anglada-Escudé and team recommend a re-evaluation of the standard methods for detecting exo-planets.