Gliese 581d: New Study Confirms Existence Of One Of Most ‘Earth-Like’ Extrasolar Planets Known

A new research study has confirmed the existence of an Earth-like planet, super-Earth Gliese 581d, orbiting red dwarf Gliese 581, after doubt was cast on its existence by a previous study conducted last year.

Confirmation of the existence of Gliese 581d is significant because it is believed to rank on astronomers’ Earth Similarity Index among the most Earth-like extrasolar planets ever found.

Planet Gliese 581d, estimated at more than two times the size of Earth, is believed to be a rocky planet with conditions that can support life.

The new study by researchers at the Queen Mary University in London and the University of Hertfordshire confirmed previous evidence about the existence of the Earth-like planet orbiting the red dwarf Gliese 581, located 22 light years away, very close on the astronomical scale.

Signals indicating the presence of Gliese 581d were first detected in April 2007 by researchers using a method called Doppler spectroscopy, or informally “wobble method.”

The method relies on observations of Doppler red and blue shifts in the spectrum of light from a planet’s parent star due to the wobbling effect of the gravitational force of the planet on its parent star.

At the time the planet was first discovered, scientists said that Gliese 581d was a super-Earth in the habitable “Goldilocks zone” of the solar system of the red dwarf Gliese 581, where atmospheric pressure and temperatures are able to support liquid water on the surface of the planet. Liquid water is considered essential for a planet to support Earth-like forms of life.

Gliese 581d was the first Earth-like planet to be found in the “Goldilocks zone” of another star.

But a study conducted last year by researchers at Pennsylvania State University cast doubt on the claims, saying that the data, on which the study’s conclusions were based, was caused not by a planet but by “activity-induced variability of the star.” The study thus dismissed the conclusions of the earlier study, describing its supporting data as “stellar activity masquerading as planets.”

But the new study by the team of researchers at the Queen Mary University in London and the University of Hertfordshire, led by Dr. Guillem Anglada-Escude, claims that the statistical techniques used in the 2014 study were inadequate for characterizing smaller planets like GJ 581d.

“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… There are always discussions among scientists about the ways we interpret data but I’m confident that GJ 581d has been in orbit around (its star) 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.”

Gliese 581
Artist's Impression Of Gliese 581 Planetary System

Anglada-Escude said the method used in the 2014 study is adequate only where the target planet is so large that data inaccuracies are comparatively too small to significantly distort results. But where the target planet is small, the otherwise minor inaccuracies become significant and could be confused with “noise” due to the variability of the parent star.

Despite the high rank of Gliese 581d on astronomers’ Earth Similarity Index, researchers say the planet’s environment would look much different from ours, with denser and toxic air bathed in dim red light from its host star.

The Earth Similarity Index only looks at factors such as surface temperature, planet density, and overall chemical composition to rank extrasolar planets on a scale 0 to 1.

The most Earth-like planet ever found was Gliese 581g, ranked 0.89. Gliese 581g is GJ 581d’s sibling planet, orbiting the same star Gliese 581.

The special interest in Gliese 581d and its “sibling” is due mostly to their relative proximity on the astronomical scale, being only 22 light years away.

According to the Independent, a researcher at the Institut Pierre Simon Laplace in Paris, said that future generations of astronomers would be able to use telescopes to observe the planet and search for life.

“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.”

Gliese 581
The Star Gliese 581

Meanwhile, scientists actively searching for extrasolar planets have said they will likely find a planet with oceans and atmosphere similar to Earth in the next 15 years, according to the Daily Mail.

John Mather, in charge of the James Webb Space Telescope (JEST) at the NASA Goddard Space Flight Center in Maryland, said, “We hope to find a planet that’s Earth-like and measure its atmosphere to work out if it has enough water on it to make an ocean. I think that will be in around ten to 15 years from now. In that time we might be able to say: ‘I can see that star over there. [Its planet] has a climate that’s like Earth and it might have life on it.'”

[Images: NSF via Daily Mail; YouTube; Wikimedia Commons]