Astronomers Dr Guillem Anglada-Escudé from the Queen Mary University of London and Dr Mikko Tuomi from the University of Hertfordshire have dismissed claims made last year that one of the exoplanets orbiting a nearby star called Gliese 581 was a ‘stellar activity masquerading as a planet.’
Gliese 581 (GJ 581) is a red dwarf star located in the constellation Libra, only 20 light-years away.
Beginning in 2005, scientists discovered a series of exoplanets around it, eventually finding evidence for four low-mass, probably terrestrial exoplanets.
In 2009, they concluded the outermost of these exoplanets, Gliese 581d (GJ 581d), orbited in the Gliese 581’s habitable zone.
With a mass of 6 times the mass of the Earth, it has been considered by many scientists to be the first truly habitable exoplanet ever discovered.
Habitable Super-Earth Gliese 581 Probably Does Exist
But now Dr Anglada-Escudé and Dr Tuomi have questioned the methods used to challenge the planet’s existence.
“The existence, or not, of 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,” Dr Anglada-Escudé, who is the first author of the paper published in the journal Science.
The statistical technique used in the 2014 study to account for stellar activity is simply inadequate for identifying small planets like Gliese 581d.
The method used before has worked when identifying larger planets in the past because their effect on the star was so significant as to negate errors in the findings. However, it makes it almost impossible to find the smallest planet signals close to or within the noise caused by the stellar own variability.
Using a more accurate model on the existing data the astronomers are highly confident that the planet’s signal is a real one, despite stellar variability.
“There are always discussions among scientists about the ways we interpret data but I’m confident that Gliese 581d has been in orbit around Gliese 581 all along.”
“In any case, the strength of their statement was way too strong.”
Dr Anglada-Escudé added: “if they 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.”