We’ve been looking at reasons why we don’t see extraterrestrials, even though many scientists are sure they must exist.One enterprising research group has now assembled Exotica, a catalog of strange phenomena in space, which might help us search more efficiently. If extraterrestrials exist and are technologically advanced, they would leave a “technosignature,” which might at first only be seen as astrange phenomenon in space:Breakthrough Listen, the initiative to find signs of intelligent life in the universe, today released an innovative catalog of “Exotica”—a diverse list of objects of potential interest to astronomers searching for technosignatures (indicators of technology developed by extraterrestrial intelligence). The catalog is a collection of over 700 distinct targets intended to include “one of everything” in the observed universe—ranging from comets to galaxies, from mundane objects to the most rare and violent celestial phenomena.JANET WOOTTEN, BREAKTHROUGH INTIATIVES, “BREAKTHROUGH LISTEN RELEASES CATALOG OF “EXOTICA” – OBJECTS OF INTEREST AS “TECHNOSIGNATURES”” AT PHYS.ORG (JUNE 23, 2020)One focus of the catalog is objects in space with extreme properties, “hottest planet, stars with unusually high or low metal content, the most distant quasar and fastest-spinning pulsar, and the densest galaxy.”Sure, something like that could be a random effect. But maybe not. For example, if you encountered an abandoned house out in the country, you might be surprised by a lack of mice. A random effect? Maybe. But what if you learn that a colony of cats lives in the basement? One thing’s for sure. You could only find out the most likely reason why mice don’t live there by investigating the basement.A second focus is “enigmatic targets whose behavior is currently not satisfactorily explained.” For example, there is Tabby’s Star, pictured above in infrared and ultraviolet, whose behavior is so strange that NASA offers nine possible explanations, including an “alien technosignature” (evidence of advanced alien activity). Why this star?:Tabby’s star, a yellow-white dwarf star located around 1,280 light-years away, was discovered in 2015, and since then it’s been a real head-scratcher. Its dimming is completely random. The depth of the dimming varies, too – it’s dimmed by up to 22 percent, and last year was caught dimming by just 5 percent.This behaviour pretty much rules out planets; when an exoplanet passes between a star and Earth as it orbits, it will dim the star by a tiny amount – 1 percent or less – at regular intervals….