There is exciting news for extrasolar planet enthusiasts. A planet smaller than Mercury has been discovered around a regular star, one similar to the sun. This is another excellent discovery done with the already very productive space telescope Kepler. The discovery was helped by the fact that the planet rotated very close to the star. After all, an astronomer needs to detect at least three signals in order to confirm a planet, and finding a planet that comes in front of the star from Earth’s view is more probable the closer it is. The latter is important because Kepler finds planets by looking at a dip in the star’s brightness caused by the plane moving in front of it.
Now, is it the smallest planet discovered ever? Possibly not, it is probably one of the planets of a pulsar system. But it kind of isn’t fair, since pulsars have a very regular rotation period, which one can measure because it sends out jets of lights that crosses the Earth everytime it rotates. One can use discrepancies in the rotational period to detect planets that are very small in mass. For the transit method, though, this is very good. It means we are well on our way to discovering rocky planets in habitable zones. We just need to observe a lot longer. Three years for an Earth sized object that goes around in one year. And we get even more variety in our discoveries, instead of just gas giants and superearths, which have been dominating discoveries because finding bigger things is easier.