It’s gratifying to see that Gliese 581 e lands right on a trend line that’s held up for over two decades and a factor of two thousand in planetary mass. It’s amazing that within a year, we’ll be in possession of genuinely Earth-mass planets orbiting nearby stars.

Exoplanetary science has been in high gear now for fifteen years; the first Earth-mass planets are a big-picture milestone, on par with the discoveries of 51 Peg b, Ups And c and d, HD 209458 b and Gliese 876 d. Even more significantly, I think that an Earth-mass planet on the books is going to catalyze a huge shift in emphasis from planetary detection to planetary characterization. The first Mars-mass exoplanet will be met with considerably less acclaim than the first Earth-mass planet. In coming years, the marquee goal of planet hunting will be to locate both representative and particularly unusual planets around the brightest stars possible…