Last month, when astronomers announced they'd found an "Earth-like planet" 20 light-years away that might be capable of supporting life, many in the scientific community were quick to point out that we shouldn't get excited just yet. After all, it was impossible to tell whether the planet, called Gliese 581 g, even had water on its surface--it just seemed to orbit its star at a distance that would allow water to exist. We had an idea of the planet's mass and its orbital properties, but we didn't know its makeup or what it looked like.

Now, it seems we don't even know whether it's there at all. A second team of astronomers has been unable to detect evidence of Gliese 581 g in the solar system, and at the moment no one can say for sure whether the planet exists or not.

  • Why We're Not Sure  At Astrobiology Magazine, Leslie Mullen explains that "planets 'tug' on the star they orbit, causing it to shift in position... By measuring the star's movement in the sky, astronomers can figure out what sort of planets are orbiting it." But in a multi-planet system like this one, measurements get murky, and "astronomers must tease out the spectral lines to figure out what represents a planet, and what is just 'noise.'" Francesco Pepe, an astronomer based in Geneva, told Mullen that based on his team's analysis, they "cannot confirm the presence of the announced planet Gliese 581 g."

  • "Stronger Than 'We Don't See It'"  Steinn Sigurðsson at ScienceBlogs adds that the new findings are "stronger than 'we don't see it'--they find that if they force a solution they get a negative signal appearing, implying the planet is not there, not just that they are not sensitive to it."

  • Give It a Year  Paul Butler, of the Carnegie Institution for Science, told Richard Kerr at Science Magazine that further study should clarify the question. ""I would expect that on the time scale of a year or two this should be settled."

  • The Lesson Here  Geekosystem's Robert Quigley shrugs that this kind of uncertainty is to be expected when "determining the existence of a planet 20 light-years away based on minute fluctuations." If nothing else, though, he says this should serve as "a reminder that before we get swept up by the triumphal popular science claims of the press, the science-science claims need to be on firm footing."