Free Astronomy Magazine September-October 2014

19 EXOPLANETS SEPTEMBER-OCTOBER 2014 planets searchers of the Pennsylvania State Univer- sity. It seems in fact certain that three of these planets do not actually exist, and two of them are, from an astrobiological viewpoint, the most interesting, GJ 581d and GJ 581g. The disappointment is rather bitter because that star is just 20.5 light- years from the Sun, and the idea that in that location may have existed a pair of Earth-type planets (although a bit bigger than ours) with conditions suitable for the T he suggestive landscape in the background wants to give an idea of how GJ 581g was imagi- ned before being struck off the exoplanets list as a result of a re- search conducted at Penn State. appearance of life was rather appealing, such that the announcement of their dis- covery had raised a certain enthusiasm; a bit too much, perhaps. The initially estima- ted masses for GJ 581d and GJ 581g were 5.6 and 3.7 times greater than Earth's (val- ues considered not particularly adverse), and, moreover, both were well positioned in the habitable zone of their star (lying be- tween 0.11 and 0.28 AU). These character- istics have in recent years motivated several