Eh, I like io9, but they're way behind on this. This planet was discovered last year.
Nature articleIn fact, it is the lightest exoplanet yet discovered.
At the time it was discovered, maybe, but exoplanet discoveries are proceeding pretty fast, and the record for smallest planet currently goes to
this.
Also, take the claim that this planet is Earth-sized with a grain of salt. Popular articles like to report the mass of planets detected via the radial velocity method as if it's the real value. It isn't. For all we know this planet could be many times heavier.
The problem is that the mass of an exoplanet is determined as a function of its orbital inclination angle. The less edge-on the orbit is from our perspective, the smaller the component of the star's velocity due to the planet we measure, and the more we underestimate the planet's mass. Therefore what astronomers are reporting is the
minimum mass, Msin
i, where
i is the inclination angle. The only ways we can only measure this angle if we can image the planet directly and trace the orbit, or if it happens to transit its host star in which case the angle is 90°. Statistically, most planets have true masses pretty close to that minimum, but it is not good to keep saying that it is equal.
Still, this is a really nice find, and does support the hypothesis that most or even all stars bear planetary systems. This was also an extremely difficult detection, requiring a radial velocity measurement precise to only half a meter per second. That's
incredible.
