Free Astronomy Magazine July-August 2016

PLANETOLOGY 10 Kelvin, thus making it even more elu- sive. The two researchers have gone even further and calculated the infrared brigh- tness of the planet also for sizes smaller and greater than 3.7 Earth diameters. This is useful for establishing if some tele- scopes have already photographed the ob- T he James Webb Space Telescope, of which we see here some mirror segments during cryogenic testing, will be one of the candidate instru- ments for discov- ering Planet Nine. [NASA/MSFC] Below, Esther Lin- der and Christoph Mordasini, the two researchers who estimated Planet Nine’s diameter and temperature. [Universität Bern] mic properties of such planet. One of these researches was conducted by Chris- toph Mordasini and Esther Linder (Univer- sität Bern), both experts in planetary evo- lution modelling. Using their own model and assuming that Planet Nine (informal name of the hypothetical object) is a smal- ler Uranus and Neptune version, the two scientists reproduced the evolution over time of some planetary parameters, start- ing from the formation of the solar sys- tem. This allowed determining the current diameter and temperature of Planet Nine. Assuming a mass 10 times that of Earth (established with previous studies), Mor- dasini and Linder found that the planet has a diameter 3.7 times that of Earth and a temperature of minus 226 degrees C, or 47 Kelvin. A so cool object emits almost exclusively infrared light, nearly entirely produced by its cooling core. The Swiss researchers calculated that the intrinsic energy of Planet Nine is about 1,000 times greater than that received from the Sun, and that in the absence of an internal heat production, the surface temperature of the object would be just