We've had our bags packed for a (hopefully) Richard Branson-led expedition to the "potentially habitable" exoplanets circling Gliese 581 for years, but there's one small hitch: new research indicates some of them might not be there. In 2007, astronomers observing the star detected four planets, with two of them in the so-called "Goldilocks zone" (not too close to the star and too hot, not too far and too cold) including one called 581d. Later in 2010, they added two more planets to the tally, including Gliese 581g, which had even better odds for life, and since then we've found others. The problem is that despite artists depictions of what a planet might be like, scientists are really just looking at "squiggles on a graph." That's what the leader of the new research, Paul Robertson said, as his team found that the measurements used to detect planets could be affected by things like sunspots, leading false indications of the two planets listed above.

[Image credit: Lynette Cook / NASA]