Free Astronomy Magazine July-August 2014

EXOPLANETS K epler-10b, the only other known planet of the Kepler-10 star system, was the first rocky planet to be discovered – in January 2011 – by the telescope whose name it bears. Above: an imagined view of Kepler-10b (Arti- st's conception). [NASA] 10c’s diameter, based on the large number of transits of the planet on the stellar disk (the revolution period is 45 days), was mea- sured at 2.35 times that of Earth, i.e. 30,000 km. This implies a density of 7.1 g/cm 3 , the highest found on a planet so far. And this time the degree of uncertainty introduced by the observational techniques is extreme- ly small, also because Dumusque’s team used the HARPS-N spectrograph (High Ac- curacy Radial velocity Planet Searcher for the Northern Emisphere) of the Telescopio Nazionale Galileo (La Palma, Canary Is- lands), perhaps the best spectrograph in the world in its field of action, capable of showing changes in the radial velocities of just 1 metre per second. Such high levels of precision and investigation can be easily thwarted by the phenomena that affect the outer layers of the star, such as oscilla- tions, pulsations, plasma movements in ac- tive regions etc. In the case of Kepler-10, however, that risk is virtually non-existent since it is a very old star: in fact it is 10.6 billion years old, an age at which ordinary phenomena are much less marked. Hence, there are no doubts about Kepler-10c oddness, which can only be a planet with the mass of a mini-Neptune concentrated in a globe that can be defined as terrestrial-size (in the broadest sense of the term). Presumably it has a rocky surface surrounded by a thin and dense atmosphere that could contain water – element which researchers do not exclude the presence of. These character- istics confirm that the amount of metals in the young universe (about 3 billion years after Big Bang) had to be more significant than generally thought, and it is therefore possible that already in those remote epochs could somewhere have appeared the first forms of life. For now, Kepler-10c is the only planet known to have those char- acteristics, but that was sufficient for creat- ing an entirely new class of mega-Earths. There is every reason to believe that it will not remain on its own for long. n