Possible 'Habitable' Planet GJ 581d Actually Exists

A certain habitable planet may actually exist, despite prior claims. Scientists have found that a planet named GJ 581d, which was first identified in 2009 orbiting the star Gliese 581, isn't a glitch in data.

The planet was first spotted using a spectrometer, which measures the "wobble" in the wavelength of light emitted by a star. This small changes in light wavelength is caused as a planet orbits a star. In 2014, though, scientists revisited the data and said that the "planet" was actually just noise in the data caused by starspots; the possible existence of the planet was then widely dismissed.

Now, though, researchers have found that this dismissal may have been too hasty. They're calling into question the methods used to challenge the planet's existence. The statistical technique used in 2014 to account for the stellar activity was inadequate for identifying small planets like GJ 581d.

That's why scientists turned a more accurate model.  Using this in combination with existing data, the scientists found that the signal from the planet was a real one, despite stellar variability. In other words, the planet exists.

"The existence (or not) of GJ 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," said Guillem Anglada-Escude, one of the researchers, in a news release. "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 the 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."

The findings are published in the journal Science.

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