Gliese 581-d has been hailed for the past seven years as one of the most promising habitable exoplanets ever discovered, with scientists deeming it the perfect Goldilocks planet. Its dwarf star, Gliese 581, is about 20 light years from Earth, and its mass suggested a rocky interior, like that of Earth. The orbital distance from its star was estimated to be just enough to support liquid water and, potentially, life.
Now, a new study suggests that previous observations of this planet were entirely mistaken, and that the existence of the planet, as well as another belonging to the system, was an illusion caused by sunspots on the Gliese 581 star. The promising planets that caused so many to grow excited about habitable zone prospects may not actually exist.
Paul Robertson at Pennsylvania State University led a team of astronomers to observe different regions of Gliese 581's spectrum. The researchers saw sunspot-like regions rotating along with the star. According to Robertson, these regions look like planets. He couldn't find any evidence of the actual, previously observed, Gliese 581-d, or of Gliese 581-g.
Gliese 581-f, another planet once thought to be habitable, was previously discovered to just be a likely trick of the eye, an illusion caused by dark spots on Gliese 581. Gliese 581-d and Gliese 581-g then began spurring wide debates. The aim of Robertson's study was to clear up the confusion and debate surrounding the existence of Gliese 581-d and -g. The conclusion was adamant-the planets are not real. Since the researchers found it likely that -d did not exist, and the detection of -g depended entirely on detection of -d, the likely conclusion seems widely supported by other astronomers.
The discovery raises questions about the recent slew of exoplanet excitement. It seems every week a new, possibly habitable exoplanet is discovered. While astronomical techniques advance at a rapid rate and accuracy in observations improve with every new telescope or piece of equipment built, the discovery of planets many light years away is still a field shrouded in uncertainty. Before we become too excited about possibilities, it might be necessary to step aside and let science take its course-observing, detecting, discovering, disproving and then observing again, until we are confident enough in the data to move forward.
Robertson and his team of researchers published their findings in Science.
