Free Astronomy Magazine September-October 2015

PLANETOLOGY The periodic signal revealing the likely pres- ence of a planet finally emerges, and a pre- liminary examination of the star’s light curve during transits allows researchers to conclude that every event lasts 10.5 hours and causes a light fall of about two ten- thousandths; all phenomena compatible with the presence on the stellar disk of a planet whose diameter is 1.1 times that of the Earth (in short, as big as Kepler-186f, if the estimated size and brightness of the star are correct). With only the observations from the Kepler telescope it is not possible to progress much further and, as standard practice, very accurate follow-up observations of the star-planet system must be made using powerful ground-based telescopes. To this end, Jenkins and colleagues took spectra of the star at the McDonald Observatory, the Fred Lawrence Whipple Observatory (Mt. Hopkins, Arizona) and the W.M. Keck Ob- servatory (Mauna Kea, Hawaii). The analy- sis of the spectra showed that the star’s properties are somewhat different from those previously estimated as, in fact, it is 11% larger than the Sun, 20% brighter and 60% richer in metals. The star’s mass (infer- red on the basis of mathematical models) and surface temperature (and thus its spec- tral type) were instead found to be similar to those of the Sun, while its age seems to T he above ani- mation shows the different Earth and Kepler-452b’s evolutionary paths, dependent on those of their stars. Based on how the extent of habitable zones is interpreted, the fate of the two planets varies con- siderably. [NASA] Right, a scaled comparison of the habitable zones of Kepler- 186, Kepler-452 and the Sun, and of the orbits of planets residing there. The inclu- sion of Venus and Mars in this dia- gram is clearly an optimistic repre- sentation of hab- itable zones. [NASA Ames/JPL- Caltech/R. Hurt] ment recorded a total of 4 Kepler-452b transits, the minimum number typically indicated by astronomers for assigning to the detected signal the planet candidate status. That signal went however unno- ticed, as it remained below the “sensiti- vity” threshold set by the assessment pro- cedures used by researchers until 2013. In May 2014, Kepler’s database was how- ever investigated with a new automated process developed by Jeff Coughlin (of the SETI Institute in Mountain View, Califor- nia), which no longer requires subjective judgments and that consults and assesses more quickly and uniformly the dataset, besides being more functional for finding smaller planets. This investiga- tion is being conducted by Joseph Twicken, member of the McDonald Ob- servatory (Uni- versity of Tex- as, Austin), to- gether with a large interna- tional team of researchers, led by Jon Jenkins, of the NASA Ames Research Center (Moffett Field, Califor- nia).