Characteristics
Gliese 581 b is about 0.04 AU from its sun. It is likely close to Gliese 436 b in mass, temperature, and (with Gliese 876 d) susceptibility to solar effects such as coronal mass ejection. Since Gliese 581 b does not transit, nothing more can be said of it yet. At the least, given that Gliese 581 b orbits alongside five other planets (Gliese 581 e, c, g, d, f) and that Gliese 436 b (thus far) stands alone, their formation must have differed.
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