In 2009, a planet named GJ 581d was spotted orbiting the star Gliese 581. Last year, claims were made the planet wasn’t a planet. It was just “stellar activity masquerading as planets.”

On Friday, researchers from the Queen Mary University of London and University of Hertfordshire released a report saying they are confident GJ 581d does exist. So, what happened with last year’s claim that it wasn’t a planet?

The researchers believe analysis used in last year’s research was “simply inadequate for identifying small planets like GJ 571d.”

The statistical technique used in 2014 is great for identifying large planets. Bigger planets have a more dramatic effect on stars. That’s not the case for smaller planets.

Gliese 581

GJ 581d’s parent star, Gliese 581

Lead author of Friday’s paper, Dr Guillem Anglada-Escude, had this to say about GJ 581d and 2014’s research.

“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.”

“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. One needs to be more careful with these kind of claims.”

GJ 581d

So, GJ 581d (also called Gliese 581d) probably exists. What do scientists think they know about the potentially habitable planet?

When it was revealed back in 2009, scientists said its rocky surface could potentially support liquid water. GJ 581d is a lot bigger than our planet, about 7 times Earth’s mass. Its radius is believed to be around twice that of Earth’s. The super-earth’s surface gravity is also believed to be about twice that of Earth’s. A bit on the high side, but if the ingredients of life are present on the planet – life could exist.

Today’s report doesn’t prove GJ 581d exists. It just casts doubt on research in 2014 saying it doesn’t. The debate about GJ 581d’s existence will continue as more research is conducted.

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