In the 1960s, Cambridge astronomers found puzzling radio pulses coming from our galaxy – pulses as regular as the best clocks. They half-seriously suggested that these might be due to LGMs, or Little Green Men. In fact, they were natural signals from dead stars. At about the same time, some Russian astronomers noted erratic radio transmissions from distant galaxies, which they also dared to propose were caused by aliens trying to get in touch. In fact, they were just giant black holes doing their thing.
There are other examples, but the lesson of history is manifest: if you give aliens the credit for strange phenomena, you’re probably wrong.
Still, skepticism shouldn’t yield to cynicism. After all, the premise that someone is out there is supported by many scientists, and no reasonable evidence should be ignored. In the case of Tabby’s star, there are also new clues. A recent analysis of Kepler data by astronomers Ben Montet and Joshua Simon has shown that this object can slowly, and unevenly, fade over the course of just a few years. Again, this is not standard operating practice for stars. It also makes explanations of Tabby’s star based on either pulverized comets or ambitious aliens trickier.