Prime Earth-Like Planet May Exist After All

Astronomers from two British universities say they’ve found evidence that one of the first discoveries of another planet that could support life really does exist, despite claims to the contrary last year.

The debate is about a planet labelled GJ 581d, believed to orbit a red dwarf planet named Gliese 581 (pictured) that lies “only” 20 light years from Earth.

Identified in 2009, it was at the time arguably the best candidate for supporting life. While believed to have twice the size and seven times the mass of Earth, it was among the most ‘Earth-like’ ever found in the ‘Goldilocks’ zone where it orbits at such a distance from a star that its temperature would allow water to exist as a liquid.

Last year, Penn State University astronomers argued that GJ 581d most likely didn’t exist. They noted it was discovered through the Doppler technique which looks for an apparent ‘wobble’ in the wavelength of light emitted by a star, caused by the gravitational pull as an orbiting planet passes between the star and a spectrometer.

They went on to argue that statistical analysis suggested the data didn’t show sufficient evidence that a planet was the cause, and that it was more likely ‘noise’ in the data caused by star spots (the name for sun spots on other stars.)

Now, though, astronomers at Queen Mary University, London and the University of Hertfordshire say the statistical analysis model used at Penn State was inadequate. They believe that analysis is only valid for cases with particularly large planets where the wobble is so significant that there’s no question of it being a matter of statistical noise. The British astronomers say they’ve used an adapted model, designed for smaller planets, that better distinguishes between a true effect and statistical noise, and that this shows it’s right to be confident that GJ 581d exists.

It could be argued that the debate is verging into philosophical territory however. The new research appears on the face of it to be less about proving the planet exists and more about proving that evidence it doesn’t exist is flawed.