Free Astronomy Magazine

8 EXOPLANETS er boundary of the habitable zone, which in the specific case of that star extends from 32.9 to 59.8 million kilometres. From the at- tenuation of the starlight during the transit of Kepler-186f, it has been calculated that the planet has a diameter 1.11 times great- er than the terrestrial one – hence 14,160 km – with a possible error margin of ± 1,800 (it could therefore be exactly as large as the Earth). As with all candidate planets discov- ered by Kepler, also for the fifth Kepler-186 planet had been necessary to carry out tests from the ground with telescopes capable of excluding any alternative interpretation of the planetary transit, relatively to the ob- served light curve. Those tests were perform- ed by a team of about twenty researchers led by Elisa Quintana (SETI Institute and NASA Ames Research Center), who made use of two cutting-edge astronomical re- search instruments, the Gemini North tele- scope (8 meters diameter) and the Keck II (10 meters diameter), of the neighbouring observatories on Mauna Kea, Hawaii. Since Kepler-186f is not sufficiently massive to produce detectable effects on the radial velocity of its star, and neither capable to dynamically perturb the four inner planets, the Quintana’s team could only prove the actual existence of that planet and exclude the existence of other objects capable of pro- ducing the same light curve. Regrettably, no telescope is today pow- erful enough to directly show an Earth-size plan- et at such a short dis- tance from a red dwarf, but it is though possible to verify if there are any other small and even fainter stars, prospective- ly close to Kepler-186, that can “mimic” the ef- fects of a planetary tran- I f Kepler-186f had an atmo- sphere compara- ble to that of the Earth, it would generally appear very similar to the latter. In the comparison above, the new planet is imag- ined with wide and deep oceans. [PHL/UPR Arecibo, NASA] From the animation on the side it can be seen how, viewed from the Earth, the transits of the 5 planets of Ke- pler-186 alter the light curve of the star. [Gemini Obs. E. Quintana et al.]