Free Astronomy Magazine September-October 2015

PLANETOLOGY on orbits whose properties are such as not to cause secondary minima in the light curve. After all tests have been completed, Jen- kins’ team concluded that there is only 1 chance in 424 that that signal is not generated by the transit of Kepler-452b, and thus the planet really exists. The fact that it does not produce effects on the ra- dial velocity of its star pro- vides us an upper limit on the value of its mass (be- yond which it would gen- erate effects detectable with current instruments). Instead, the diameter cal- culated for the planet and reasonable theoretical eval- uations do provide us a low- er limit of that value. The two extremes are 7 and 3 Earth masses and, subse- quently, what we are fac- ing is not exactly a twin of our planet. In the best of cases its gravity would be double that keeping us glued to the ground and, according to the experts, this implies an atmosphere considerably thicker than ours, perhaps fuelled by in- tense volcanic eruptions. On this last point we could express some doubts, since with the data available we do not have the certain- ty that Kepler-452b has a rocky surface; a scenario that Jenkins’ team consid- ers likely at about 49-62%. For complete- ness’ sake, it should also be pointed out that without an intervention of Kepler- 452b in the radial velocity of KIC 8311864 it is not possible to know the eccentricity of the planetary orbit, and hence not even its exact shape. This in turn has an impact on the effective permanence of the planet nal such as that attributed to it may in fact have a different origin. Consequently, re- searchers needed to start ruling out all pos- sible alternative scenarios: eclipsing binary stars laying along the line of sight; a faint companion star transited by a big planet; the transit of a white dwarf companion or the occultation of a brown dwarf, located accurate mathe- matical models, bodies of this size do not have more than a 40% chance to have a rocky surface. [NASA Ames/JPL- Caltech/T. Pyle]