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'Habitable' Planet Previously Ignored by Scientists

Mar 06, 2015 02:19 PM EST
planet GJ 581d
Pictured: An artist's impression of what the planet GJ 581d might look like.
(Photo : Queen Mary, University of London)

The search for life on planets outside our solar system has been long and arduous, so when recent research revealed that scientists previously ignored one such "habitable" planet, needless to say it was shocking.

However, don't go throwing your arms up in outrage just yet. It turns out the mistake was due simply to an inadequate data analysis.

The planet, named GJ 581d, was first discovered in 2009 orbiting the star Gliese 581 some 20.5 million light-years away. It was spotted using a spectrometer that measures its Dopler shift, or "wobble" - small changes in the wavelength of light emitted by a star, caused by the orbiting planet. The theory is that the nature of these planets can be measured based on how they affect the star that they orbit.

According to, initial observations indicated that GJ 581d has a surface temperature that is cool enough to allow water to pool on the surface, which means it could possibly support life. However, just last year scientists rescinded their discovery, determining that it was too good to be true. They blamed their mistake on noise in the data caused by internal star activity, and not the presence of a hospitable world.

But now, researchers from Queen Mary University of London (QMUL) and University of Hertfordshire show that GJ 581d was in fact not masquerading as a planet, and that scientists got things right the first time around.

"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," Dr. Guillem Anglada-Escudé, who led the study, said in a news release.

The Goldilocks-zone is simply the distance from a star that will allow a planet habitable conditions that are "just right" for life.

It was determined that the problem was with the statistical technique scientists used in the 2014 research. The method has worked just fine in the past for larger planets because their effect on the star was too significant to ignore. But by taking the same approach to GJ 581d, a considerably small planet, it set researchers up for disaster. It makes it almost impossible to find the smallest planet signals close to or within the noise caused by the stellar variability.

By using a more accurate model on the existing data, the QMUL team has put GJ 581d back in the running as a strong candidate for a habitable planet outside of our solar system.

The new findings were reported in the journal Science.

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