Free Astronomy Magazine November-December 2015

ASTROBIOLOGY mostly in novels, movies and science fiction TV series. In an article published in Science in the summer of 1960, Dyson pointed out that megastruc- tures of that kind would re- lease, as they heat up, an amount of infrared radiation not attributable to the star, a property that could have been exploited by us in the search for possible extraterrestrial civ- ilizations (unless these civiliza- tions have found a way to pre- vent any form of heat dissi- pation...). Even more evident than the infrared excess could however be the drops of brigh- tness in the visible light of the stars surrounded by the mega- structures, drops whose extent would depend on the form and movement of the latter. Leaving aside the hyperbolic case of a closed Dyson sphere, let us rather think of the case of rings or multiple bands of solar panels as wide as planets: if in cer- tain geometric and dynamic circumstances they were to occasionally interpose be- tween the star and a distant observer, they would cause the occultation of a not insig- nificant part of the stellar surface and hence a considerable dip in brightness. Unlike the transit of a planet, that typically causes very modest occultations, always of the same size, same duration and at regu- lar intervals, the transit of megastructures would produce more severe and unpredic- table events. When in 2009 NASA's Kepler space telescope went into action, the pos- sibility to record the effects of possible transits of megastructures on the disks of distant stars became reality. Kepler moni- tored for four years the photometric behav- iour of more than 156,000 stars in a small region of sky between the constellations of Lyra, Cygnus and Draco. As it happens more and more often, as part of observa- tion campaigns producing huge amounts of data, in the preliminary analysis of the latter were also involved numerous volun- teer amateur astronomers whose task was to sift through thousands of light curves in order to find traces of any transits. This A bove, a Dys- on sphere almost totally closed, formed by giant hexagonal panels. [Jay Wong] Below, the unex- plained light curve of KIC 8462852, with two deep minimums record- ed by Kepler. [T. Boyajian et al.]