Free Astronomy Magazine September-October 2015

PLANETOLOGY and being habitable are two very differ- ent things: if the star-planet system’s esti- mated age is correct, the evolutionary stage reached by KIC 8311864 has probably al- ready triggered an out of control green- house effect on the planet, which re- searchers estimate to be underway by about 800 million years. Moreover, the distance of the star is not known with absolute precision (we will know it better within 1-2 years thanks to Gaia space tele- scope) and it could even be more far-away than previously estimated; in that case the planet, already classified as super-Earth, could be even bigger and belong for sure to the mini-Neptune class. (In a very thor- ough article published in The Astrophysical Journal in March 2015, Leslie Rogers, Cal- tech, places the confine between super- Earths and mini-Neptunes precisely at 1.6 solar masses.) In short, Kepler-452b does not at all seem to be an Earth’s twin and even the “older cousin” name given to it would seem inappropriate. The chances of finding in Kepler’s database something much more similar still however plentiful, given that researchers are already examining a further 65 candidate planets with diameters between one and two times that of our own planet, all orbiting in the habitable zones of their stars. If not even among them it will be possible to identify a new Earth, we will have to wait for future observations by two new NASA space telescopes currently in an ad- vanced construction stage, the Transiting Exoplanet Survey Satellite and the James Webb Space Tele- scope, scheduled for launch in 2017 and 2018. Together they will discover Earth-sized plan- ets also at relatively short dis- tances from our own, provide direct information on their size, mass, atmosphere, colours, sea- sonal variations and weather, including the possible presence of vegetation. So far we have evidence of about 5,000 plan- ets, 1,500 of which have already been confirmed. Almost all of them were discovered just with the transits method in a tiny corner of the heavens represent- ing 0.28% of the entire sky. We can just imagine how many non-transiting planets there are and how many planets there are in total in the remaining 99.72% of the sky. L ight curve of KIC 8311864 in the 60 hours cen- tred (phase 0) on the 4 transits of Kepler-425b, of 10.5 hours each. The black dots are the photo- metric observa- tions of Kepler, the blue circles the averaged val- ues. The moder- ate dispersion can be attributed to photospheric activity. [Jenkins et al.] Below, in the first half of 2015 there was a significant in- crease of new planet candidates (yellow dots) in Kepler’s data- base, thanks to the introduction of a new assess- ment procedure. n